ESE's works engine tuner

[F5 Dave]

What about licorice?

[peewee]

Thats easy to logic thru. When you see the pressure traces in EngMod ( or even last century in Dynamation ) , at TPO there is more residual Blowdown pressure above the port , than in the case , below it.
Thus this positive P delta, causing reverse flow back into the duct , affects the first opening port the most , this gave rise to the " first to open , last to flow " premise.
It is in fact how port stagger scavenging regimes actually work at all.
Also explains why power drops with excess Blowdown STA numbers.

im sure jan explained it hundreds of pages back. was his reason for leaving the A roof 1* lower so the aux exh could be slightly lower or the last to open first to flow like you say ?
im in the early grinding stages on my yami barels and not sure yet how i will go. front side power i dont think i need it as ive got the 2-5 clutchless shifting trans and the ratios seem to be gapped close on the banshee

[wobbly]

The Aprilia /Rotax had reverse stagger before Jan arrived .
And the Banshee , like its old LC cousin with no PV , benefits hugely from normal port stagger.
Its 3-4 shift drop is huge , this is easily fixed with Nova semi race gears - you dont need the full set if drag racing it.
But also the Banshee , like the RZ/YPVS has the B port pointing at the plug , completely at odds with SOTA scavenging principles - reversing the axial up angles on the A/B ports needs epoxy and roof welding and
its twice as effective as anything stagger can achieve.

[Frits Overmars]

hey wobbly how many things do you and frits disagree on ? besides if the A or B transfer should open first
Nothing that i can remember , except a long time ago about the values of peak cylinder pressure - but I am also sure Frits agrees that reverse stagger scavenging favors top end and gives room for bigger Aux ( along with less A port short circuiting ), plus the higher B,C are wider thus naturally gives more transfer STA to match high Blowdown. Normal stagger favors front side power and is ideal if there is no PV - and or for naturally more mid for MX etc..I agree with your every word Wob, including that pressure issue, where once upon a time a factor of 2 had mysteriously disappeared from my calculations.


maybe it wasn't which port should open first but if the one to open first flows first. im sure frits will set me straight I could try, but I've tried to do it before so I'm not going to hold my breath.
It's not rocket science, it goes like this: if you open a port over which there is a pressure difference, a flow will start. If you open a second port one millisecond or one crankshaft degree later, a flow through that second port will start one millisecond or one crankshaft degree later.
In short: the port that opens first, flows first, though not always in the desired direction; that depends on the pressure difference.
I know of course what Wobbly means. I'm not arguing for the sake of contradicting him but rather for the sake of pulling his leg.


Toroidal vs Bathtub?I'm not contradicting Wobbly, I'll get to that in a minute, but first I need to have a word with you, Husa. I have a strong suspicion that your 'bathtub' is in fact a hemispherical combustion chamber. I'm not familiar with your sanitary facilities, but over here a bathtub looks like this:
351568

And since we're splitting hair anyway, I've seen combustion chamber shapes called Top Hat, but that is about the worst shape you can have in a two-stroke (side-valve foul-strokes are even worse). Luckily most people who say Top Hat really mean Bowler Hat, which is a lot better.
351569

OK, over to the toroids, better known as donuts in some circles. The blue drawing shows the RSA combustion chamber dimensions.
From point 2 to point 3 we see a quarter circle and the characteristic of a toroid is that the center of this quarter circle is not on the central vertical axis of the chamber, but off center.
351571
It used to be thought that a hemispherical chamber was best for a rapid burn, but we know now that the rate of burn mainly depends on turbulence, and a toroid is the best shape to exploit the squish effect, as seen on the blue+yellow drawing.
351570

We can extend the circular arc between point 2 and point 3 beyond point 3 and then we get a combustion chamber with an intruding spark plug, like on the picture below.
351572

The radially inward flow due to the squish is symmetrical, so an intruding spark plug that brings the spark to the center of the action would seem to make sense. But the scavenging column that must expel the spent gas from the combustion chamber before the squish can become effective, is not symmetrical. That column moves upwards along the cylinder wall oposite the exhaust, and then performs a looping as it follows the outer contour of the combustion chamber. An intrusion hanging from the chamber roof may throw a scavenging shadow and so hamper the scavenging.

While Wobbly has determined that the intruding toroid is the best shape when combined with a flat-top piston, Jan Thiel has determined that due to the Coanda effect a domed piston is better with regard to transfer flow and piston cooling. I am not sure whether Jan, after his comparison tests of flat-top and domed pistons, has tested the combination of a flat-top piston and an intruding toroid.

351573
Today's final picture is for Wobbly. Happy Birthday Wob !

[wobbly]

Good thing Frits is that if you pull my leg , I dont fall over - and Rocket Science is easy compared to 2T technology..
The Chief Engineer at Yamaha , nicknamed " Suzan " many years ago told me that viewing the squish action in a super high speed camera of some sort , his assertion was that the turbulent stream exiting the squishband
remained attached to the chamber wall - thus rotated in the opposite direction. Maybe he was pulling my leg , I always wondered.
The Toroid testing I did was many years ago , now I cant use one in what has become the focus of my work - KZ kart engines.
But it has recently been proven that a semi flat top ( a conic with 50% area flat ) is superior with a bath tub chamber as well , I just need the time to do an optimum timing edge radius test to finish of that area of development.
And thanks for the spark plugs today as well - what more could a man want , apart from liqorice.

[husaberg]

I'm not contradicting Wobbly, I'll get to that in a minute, but first I need to have a word with you, Husa. I have a strong suspicion that your 'bathtub' is in fact a hemispherical combustion chamber. I'm not familiar with your sanitary facilities, but over here a bathtub looks like this:
351568

And since we're splitting hair anyway, I've seen combustion chamber shapes called Top Hat, but that is about the worst shape you can have in a two-stroke (side-valve foul-strokes are even worse). Luckily most people who say Top Hat really mean Bowler Hat, which is a lot better.


OK, over to the toroids, better known as donuts in some circles. The blue drawing shows the RSA combustion chamber dimensions.
From point 2 to point 3 we see a quarter circle and the characteristic of a toroid is that the center of this quarter circle is not on the central vertical axis of the chamber, but off center.
351571
It used to be thought that a hemispherical chamber was best for a rapid burn, but we know now that the rate of burn mainly depends on turbulence, and a toroid is the best shape to exploit the squish effect, as seen on the blue+yellow drawing.
351570

We can extend the circular arc between point 2 and point 3 beyond point 3 and then we get a combustion chamber with an intruding spark plug, like on the picture below.
351572

The radially inward flow due to the squish is symmetrical, so an intruding spark plug that brings the spark to the center of the action would seem to make sense. But the scavenging column that must expel the spent gas from the combustion chamber before the squish can become effective, is not symmetrical. That column moves upwards along the cylinder wall facing away from the exhaust, and then performs a looping as it follows the outer contour of the combustion chamber. An intrusion hanging from the chamber roof may throw a scavenging shadow and so hamper the scavenging.

While Wobbly has determined that the intruding toroid is the best shape when combined with a flat-top piston, Jan Thiel has determined that due to the Coanda effect a domed piston is better with regard to transfer flow and piston cooling. I am not sure whether Jan, after his comparison tests of flat-top and domed pistons, has tested the combination of a flat-top piston and an intruding toroid.

351573
Today's final picture is for Wobbly. Happy Birthday Wob!


A picture paints a thousand words and a thousand words paints a picture thanks for the explanation.

My description was clumsy, Yes your first pic is the std 4t like version of a bathtub.
much like a modified dutch ABSA Goldstar or a million modified harleys.
i cant find a pic of the Dutch BSA version i have posted it before but it looks like this hardly Davidson aftermarket one below.
https://www.hdforums.com/forum/attachments/evo-classic-models/411332d1419657922-which-heads-would-you-pick-20141224_154357.jpg


What i was meaning was this cross section of a bathtub
351574

I never asked if the Dutch ABSA had tulip valves.:msn-wink: but on either of the bathtub head the plug is at the top. is the traditional usage.
The worst head shape i have seen was open Villiers. The top hat at least had a squish band.
351575

okay i found this Villiers one i had not seen.
351576
you would think the wider end would be near the plug not further away.

Funny enough villers was the first time i seen a toridal term used
351577
It was stolen from a 1960's diesel.
I don't think it was ever manufactured in this from. well I hope it wasn't

[Frits Overmars]

Funny enough villers was the first time i seen a toridal term used
351577
It was stolen from a 1960's diesel. I don't think it was ever manufactured in this from. well I hope it wasn'tYou can abandon all hope, Husa. Villiers reported problems with their toroidal cylinder head, and you don't get those unless you actually manufacture and run it.
351579
One consolation: the toroidal head never made it to serial production.

[oldjohnno]

Apologies if this has been discussed previously. I've been wondering about the evolution of 2Ts from the 70's to today, and a couple of the things that stand out are the understanding of blowdown and the dramatic increases in transfer area. Back then it was thought that too much transfer T/A was detrimental and people like Jennings warned against it. Now, we basically ring the cylinder with transfers and make much more power. What has enabled the use of so much more transfer area when previously it reduced output?

[F5 Dave]

I'll take a stab at this. The quantum change was the shift in reliance on using the bottom end as a pump, to the pipe creating increasingly stronger forces. Everything else then needed to evolve to keep in step with that and transfer control became critical as did more and more blow down area.

As usual you have to change everything to gain proper advantage with less detrimental effects that warned off early experiments (Jennings working with limited resources).

[Flettner]

You can abandon all hope, Husa. Villiers reported problems with their toroidal cylinder head, and you don't get those unless you actually manufacture and run it.
351579
One consolation: the toroidal head never made it to serial production.
I wonder, was that because they didnt have a decient ignition to compliment it?

[oldjohnno]

I'll take a stab at this. The quantum change was the shift in reliance on using the bottom end as a pump, to the pipe creating increasingly stronger forces. Everything else then needed to evolve to keep in step with that and transfer control became critical as did more and more blow down area.

As usual you have to change everything to gain proper advantage with less detrimental effects that warned off early experiments (Jennings working with limited resources).

And possibly the new exhaust ports, having more area at the top (in order to improve blowdown) had a side effect of providing a stronger initial wave in the pipe, which in turn provided a stronger negative wave to pull from the transfers?

[Grumph]

I wonder, was that because they didnt have a decient ignition to compliment it?

Around the time of the Starmaker there were some pretty good aftermarket ignitions about. The two Starmakers that i've had through the workshop weren't stock in that area. One had points and a battery powered coil. I converted that to a Pertronix trigger with a good modern coil. Goes well with extra transfers and the squish set correctly.
The other one has a Femsa self generating ignition. I believe a period available aftermarket fitting. Probably originally for a Bultaco. Still pretty stock elsewhere. Goes well.

These engines are much underrated. Compared to traditional Villiers they're night and day.

I suspect the toroid was expensive to produce and didn't produce any more power than a conventional squish head. Production engineering wins out.

[peewee]

hey guys im trying to make a paper template of the exh roof then cut it out to mark the bore for grinding but its looking more arched than i thought. i used what frits posted. 75% bore is center radius. maybe i bungled it somehow. but see the photo to be sure.
the other thing im trying to figure out is if you lengthen the exh passage how will the pipe react . original the passage length is 85% of bore. now its 171%. do you think the pipe might need to be significantly shorter or it wont matter much ? engmod could probly tell me but im not that good with using it



https://i.ibb.co/0YtbH5f/20220820-190023.jpg

[wobbly]

The toroidal shape of the Starmaker has a fatal flaw , the turbulent eddies off the squish corner don't impinge at all on the main body of the chambers trapped A/F volume.
Those eddies are pointed at the plug , but the vast majority of the compressed volume is shrouded - thus wont see the effect of turbulence increasing the flame speed at all.

As far as the gradual change in design approach after the 70's period , is that prior to this point it wasn't appreciated how important Blowdown STA was to achieving power gains.
Thus we had amazing new high tech graphs , showing Transfer and Total Exhaust angle area only.
Case pumping only works in lawnmower 2T's , and as pipe design efficiency slowly increased so did the cylinder depression created around BDC needed to draw mixture thru the transfer ducts.

Then it soon became obvious that the old first tuning choice of case stuffing , didn't work anymore.
At that juncture making the Transfer STA bigger didn't work for two reasons , flow reversal into the transfer ports due to way too high remnant blowdown pressure , and secondly the bigger exit area compromised the flow streams
coherency due to lack of velocity.

Moving ahead to todays SOTA approach , we now end up with all the available radial area filled with transfer width , and the axial heights are set such that both the Blowdown and Transfer STA match synergistically.
Move the transfer axial height up , and blowdown is compromised , move it down and you loose transfer STA , but just as important is that an excess of Blowdown STA reduces the available remnant pressure.
The correct amount of this is needed to maximize the efficiency of the transfer stagger concept , on the scavenging and trapping regimes.

[andreas]

hey guys im trying to make a paper template of the exh roof then cut it out to mark the bore for grinding but its looking more arched than i thought. i used what frits posted. 75% bore is center radius. maybe i bungled it somehow. but see the photo to be sure.
the other thing im trying to figure out is if you lengthen the exh passage how will the pipe react . original the passage length is 85% of bore. now its 171%. do you think the pipe might need to be significantly shorter or it wont matter much ? engmod could probly tell me but im not that good with using it



https://i.ibb.co/0YtbH5f/20220820-190023.jpg

There is something called a flat-width in the drawing, What is it? Seems like it should be the chord width, but here it is 51 mm. I belive Frits suggests smaller radius at the corners also. How is the ex-duct lengthen? Generally the tuned length should be same, unless you wish to alter it.

[peewee]

There is something called a flat-width in the drawing, What is it? Seems like it should be the chord width, but here it is 51 mm. I belive Frits suggests smaller radius at the corners also. How is the ex-duct lengthen? Generally the tuned length should be same, unless you wish to alter it.

yes there will be corner radius but i didnt draw it yet because the roof looked more arched than what i thought it would be. i might not understand what 75% bore=center radius.
45.5mm chord is 51mm flat on paper to draw the shape if that make sense.
the passage is lengthen by cutting off the outer shell and welding on a extra passage and welding back on new outer shell

[andreas]

I see now, it's for the templet. Would suppose the formula is for the port as it appears in the cylinder, and not the templet. If the tuned length is increased by 55mm, that isn't peanuts.

[husaberg]

The toroidal shape of the Starmaker has a fatal flaw , the turbulent eddies off the squish corner don't impinge at all on the main body of the chambers trapped A/F volume.
Those eddies are pointed at the plug , but the vast majority of the compressed volume is shrouded - thus wont see the effect of turbulence increasing the flame speed at all.



the sales blurb had the toridal head i assume in grossly exaggerated form
i did a bit of digging and the original engine drawings never had it .
The starmaker was by pommy standards of the time a pretty nice try.
The designer had spent a fairy bit of time with Herman Meier.
They used all the knowledge they had.
later variants were to be unit construction the diaphragm clutch is pretty cool and predates the other British ones.
i believe the biggest flaw was the 4 speed gearbox.
According to the person that designed it they made 100 6 speed I only have seen mention of maybe 10.
351591351593351594351595

https://ajsstormer.wordpress.com/2020/06/10/symphony-for-the-devil-2020/
https://ajsstormer.wordpress.com/2017/07/31/first-blog-post/

https://ajsstormer.wordpress.com/chapter-3/
https://ajsstormer.wordpress.com/chapter-10/

[Grumph]

The six speed box is a nice piece of work. Needle bearings everywhere. One of the 2 through here had the six speed fitted to the engine but the frame had not been altered to fit it. I finished the job. Amusingly, when contacted, Fluff Brown's son in the UK who now runs the Starmaker business, had never seen a six speed box. He had to ask an old guy on staff how much and which oil it took. Nothing's written down apparently. FWIW, there's a level plug. Oil is your choice.
Some things never changed even though the design was a huge step forward.

Again FWIW the CR 4 speed box suits the standard porting and pipe quite well. No problems keeping it on the pipe on track at all. If they'd got their act together in good time, they could have sold a lot of entry level 250 racebikes. Next step up - and better engineered - than the Greeves. Probably cheaper to run - in the UK - than a TR250 or TD2.

[andreas]

Something I never quite understod: tire grip depending on contact area, obviously area is irrelevant for friction with solid materials. I've thought this applies to tires also, but general consensus seem to disagree. What say you?

[F5 Dave]

Look up Shear

[andreas]

Dave, which Shear is that?

[F5 Dave]

Well don't Google Sheer. That will probably get you pictures of Tights. So the other Shear..

10 second Google search which i haven'treally read bit should get you started. :

https://pediaa.com/difference-between-friction-and-shear/

[andreas]

Thanks for clarifying that.

[husaberg]

Something I never quite understod: tire grip depending on contact area, obviously area is irrelevant for friction with solid materials. I've thought this applies to tires also, but general consensus seem to disagree. What say you?

In NZ Tyres are anything but solid objects contact patches move and are dependant of shape and pressure and the tire is part of the suspension system whether we like it or not. With friction. why have a slipper pistons single rings skinny tyres on racing pushbikes small frontal areas large disc brakes fat rear tires on drag lso bikes. When the area or cross section is smaller with these things they tend to be also lighter skinnier more area and slippery so whilst it was seem not to change due to the other factors it does overall.
i know what you are saying in regards to Physics with the solid objects, but there are more factors than friction and area


The force due to friction is generally independent of the contact area between the two surfaces. This means that even if you have two heavy objects of the same mass, where one is half as long and twice as high as the other one, they still experience the same frictional force when you drag them over the ground. This makes sense, because if the area of contact doubles, you may think that you should get twice as much friction. But when you double the length of an object, you halve the force on each square centimeter, because less weight is above it to push down. Note that this relationship breaks down when the surface area gets too small, since then the coefficient of friction increases because the object may begin to dig into the surface.


Frits can fix what i have wrong

This doesn't explain why its easier to push things with wheels .............

[andreas]

What do the slipper pistons say about things? And tires are not regarded as solid matter here either.
I don't know, therefore the question. Of course there is no concern for longegivety or cases where the material isn't within it's structural limits.

[QUOTE]
As an engineer, I know that friction does not depend upon surface area. As a car nut, I know that wider tires have better traction. How do you explain this contradiction?
Asked by: Mark Secunda

Answer
This is a good question and one which is commonly asked by students when friction is discussed. It is true that wider tires commonly have better traction. The main reason why this is so does not relate to contact patch, however, but to composition. Soft compound tires are required to be wider in order for the side-wall to support the weight of the car. softer tires have a larger coefficient of friction, therefore better traction. A narrow, soft tire would not be strong enough, nor would it last very long. Wear in a tire is related to contact patch. Harder compound tires wear much longer, and can be narrower. They do, however have a lower coefficient of friction, therefore less traction. Among tires of the same type and composition, here is no appreciable difference in 'traction' with different widths. Wider tires, assuming all other factors are equal, commonly have stiffer side-walls and experience less roll. This gives better cornering performance.
Answered by: Daryl Garner, M.S., Physics teacher MacArthur High School, Lawton, OK

Friction is proportional to the normal force of the asphalt acting upon the car tires. This force is simply equal to the weight which is distributed to each tire when the car is on level ground. Force can be stated as Pressure X Area. For a wide tire, the area is large but the force per unit area is small and vice versa. The force of friction is therefore the same whether the tire is wide or not. However, asphalt is not a uniform surface. Even with steamrollers to flatten the asphalt, the surface is still somewhat irregular, especially over the with of a tire. Drag racers can therefore increase the probability or likelihood of making contact with the road by using a wider tire. In addition a secondary benefit is that the wider tire increased the support base and makes it hard to turn the car over in a turn or in a mishap.
Answered by: Stephen Scholla, B.A., Physics Teacher, Vienna, Virginia[QUOTE]

Including these quotes just to show some different opinion.

[Peljhan]

What do the slipper pistons say about things? And tires are not regarded as solid matter here either.
I don't know, therefore the question. Of course there is no concern for longegivety or cases where the material isn't within it's structural limits.

Including these quotes just to show some different opinion.

I asked myself this question right when we learned in high school about friction but physics teacher didn't know the answer.
Researched and made an explanation to myself few years ago when I was at university and had a debate with friend.
I came to conclusion that you can't apply basic friction rules to tires as friction surface is not relatively smooth.

If you look tires and asphalt contact you get small teeth that bind or interlock with eachother.
Imagine having a gear rack made of steel fixed on a table. You put another rubber gear rack on steel rack so they interlock teeth with eachother. If you use longer racks with more teeth (same teeth size), you will need more horizontal force to skip teeth.

This phenomenon is called mechanical adhesion.

[andreas]

It's complex, There is the interlocking you mention, but the number and depth of those "teeth" must depend on the pressure, which will decrease as the tire gets bigger-very similar to basic fricton law. Similar but maybe The shear -friction can explain it more precise, we'll see.

[Frits Overmars]

Frits can fix what i have wrong.Yeah right. Your confidence is heartwarming Husa, but I don't even know if I should write tires or tyres.

[Vannik]

On tyres:

The grip coefficient is made up of three components:

1. Friction coefficient
2. Interlocking coefficient - the soft rubber hooking on the surface roughness
3. Adhesion - between the rubber and the surface

2 and 3 increases quite dramatically with increase in tyre temperature.

[andreas]

On tyres:

The grip coefficient is made up of three components:

1. Friction coefficient
2. Interlocking coefficient - the soft rubber hooking on the surface roughness
3. Adhesion - between the rubber and the surface

2 and 3 increases quite dramatically with increase in tyre temperature.

It's fair to read this as that contact patch-area is more like a secondary factor?

[JanBros]

On tyres:

The grip coefficient is made up of three components:

1. Friction coefficient
2. Interlocking coefficient - the soft rubber hooking on the surface roughness
3. Adhesion - between the rubber and the surface

2 and 3 increases quite dramatically with increase in tyre temperature.

fuck temperature, we want to know about surface area :)

[wobbly]

IMHO , yes we have the 3 factors as described by Neels.
But in the scenario of a tyre on asphalt we do not have the mass of a smooth block - sliding down a smooth plane on an angle , generating a prescribed Coefficient of Friction, as we all saw in Physics 101.
This is a specific context ( and the only one ) where contact area is classically deemed irrelevant.

But with one element having the highly deflective " sticky " characteristics of " rubber " and the other being an entire surface of solid peaks and valleys , any downward force on the rubber increases the mechanical adhesion
between these two very dissimilar surfaces.
Increase the area of interlocking adhesion ( contact patch area ) and the number of adhering points of mechanical contact increases.
Thus increasing the mechanical grip level.

This gives rise to the concept of the traction circle , wherein a downward force acts on an area of rubber in contact with the asphalt , and this generates an available level of grip that is a finite metric.
Increase the traction used in the direction of travel ( braking or accelerating ) then the level of traction available perpendicular to this ( sideways cornering ability ) is reduced , and visa versa.

Proof of this lies in the fact that a softer rubber in the contact patch area , will be torn off the underlying carcass , and be left behind on the asphalt faster than a harder version.
This torn off rubber adheres to the asphalt to such an extent that in Moto GP , and even more so in karting , there is , in certain parts of the track no asphalt to be seen.

Then we have sticky rubber adhering to even more sticky rubber , the result being high sides in MotoGP , and karts tipping up on the two outside tyres, due to so much mechanical grip between the surfaces.
Thus a wider tyre , or a softer tyre , does increase the Coefficient of Friction ( grip ) , between the two surfaces - as neither are smooth by the classic definition used in Physics 101.

[husaberg]

Yeah right. Your confidence is heartwarming Husa, but I don't even know if I should write tires or tyres.

i did see that but i am having mouse issues it has a mind of its own anyone know why my curser and highlight function is acting odd.

[HenkS]

hey guys im trying to make a paper template of the exh roof then cut it out to mark the bore for grinding but its looking more arched than i thought. i used what frits posted. 75% bore is center radius. maybe i bungled it somehow. but see the photo to be sure.
the other thing im trying to figure out is if you lengthen the exh passage how will the pipe react . original the passage length is 85% of bore. now its 171%. do you think the pipe might need to be significantly shorter or it wont matter much ? engmod could probly tell me but im not that good with using it



https://i.ibb.co/0YtbH5f/20220820-190023.jpg

What about those 75%, I did not read any reply on that.
75% can't be good !

[andreas]

IMHO , yes we have the 3 factors as described by Neels.
But in the scenario of a tyre on asphalt we do not have the mass of a smooth block - sliding down a smooth plane on an angle , generating a prescribed Coefficient of Friction, as we all saw in Physics 101.
This is a specific context ( and the only one ) where contact area is classically deemed irrelevant.

But with one element having the highly deflective " sticky " characteristics of " rubber " and the other being an entire surface of solid peaks and valleys , any downward force on the rubber increases the mechanical adhesion
between these two very dissimilar surfaces.
Increase the area of interlocking adhesion ( contact patch area ) and the number of adhering points of mechanical contact increases.
Thus increasing the mechanical grip level.

This gives rise to the concept of the traction circle , wherein a downward force acts on an area of rubber in contact with the asphalt , and this generates an available level of grip that is a finite metric.
Increase the traction used in the direction of travel ( braking or accelerating ) then the level of traction available perpendicular to this ( sideways cornering ability ) is reduced , and visa versa.

Proof of this lies in the fact that a softer rubber in the contact patch area , will be torn off the underlying carcass , and be left behind on the asphalt faster than a harder version.
This torn off rubber adheres to the asphalt to such an extent that in Moto GP , and even more so in karting , there is , in certain parts of the track no asphalt to be seen.

Then we have sticky rubber adhering to even more sticky rubber , the result being high sides in MotoGP , and karts tipping up on the two outside tyres, due to so much mechanical grip between the surfaces.
Thus a wider tyre , or a softer tyre , does increase the Coefficient of Friction ( grip ) , between the two surfaces - as neither are smooth by the classic definition used in Physics 101.

Thanks Wobbly, for the extensive answer. Do you also have an appreciation of how large the adhesion part of the total grip may be?

[husaberg]

uncle kevin
https://www.cycleworld.com/2013/12/27/ask-kevin-does-a-larger-motorcycle-tire-footprint-increase-grip/

Contact patch diagramOf the two contact patches above (left and middle image), which has the most grip? The one in the middle, with more rubber touching the road. At right, the contact patch of a bike at a healthy lean

QUESTION: I believe you’ve gotten the physics incorrect in your “Control the Contact Patch” sidebar (“The Pace 2.0” by Nick Ienatsch). A bigger contact patch does not give a tire more resistance to sliding: The force of friction is proportional to the normal force (F=mu x N), where F is along the surface and N is perpendicular to it, and mu is the coefficient of (static) friction.


The force of friction parallel to the road surface (“grip”) is equal to the coefficient of static friction times the normal force, which is the weight on the tire. If the size of the contact patch alone caused greater friction, then putting a wider tire on a motor­cycle would automatically give more grip. It doesn’t.

Owen Hayes
Philadelphia, Pennsylvania

ANSWER: Amonton’s Law for physics describes the behavior of many elastic solids. Friction is directly proportional to the area of actual contact between the two solids, which is normally only a small percentage (like five percent) of the apparent area of contact.

If the solids have linear elasticity, then doubling the force pressing the two surfaces together will double the area of actual contact, and that, in turn, will double the frictional force required to slide one across the other. Linear elasticity is essentially the same as saying the material has a constant, rather than progressive spring rate.

Rubber does not display linear elasticity. Instead, it has a “rising spring rate.” An applied light load pushes a lot of rubber into actual contact. When that load is doubled, you do not get doubled area of actual contact because the rubber is stiffening. A better strategy, therefore, is to double the area of apparent contact. With tires, this is the footprint area. This is why the tires of racing cars are so extremely wide.


Nick writes about what goes on as the rider transitions from braking to throttle in mid-corner and the importance of maintaining the size of the footprint by never allowing the tire to significantly unload. Being the weird material it is, rubber sliding on an uncontaminated glass surface can produce friction as high as 10 times the applied load. If this could be achieved on highway or racetrack, riders would be dragging their faceshields.


plus some car thing i found that makes sense

351612
especially the skinny tyres in the wet and snow as this makes the road like a physics flat surface.

[andreas]

Interesting, Husa.

[peewee]

What about those 75%, I did not read any reply on that.
75% can't be good !

what do you say. did i get it wrong?


https://i.ibb.co/7S0vTF8/20220825-193037.jpg

[Frits Overmars]

What about those 75%, I did not read any reply on that.
75% can't be good !Would you mind telling us why "75% can't be good !" Henk?

[andreas]

The point, I think, is not that far fetched: Why not use a 180 front tire if it offered a substancial increase in grip-50% wider, it should more than well make up for a more cumbersome stearing that could be adapted by the riders and also the frame geometry.

[HenkS]

Would you mind telling us why "75% can't be good !" Henk?

Much to round and besides it does't look at all to the rouding of that blue and red example.
Peewee makes the drawing just right 75% of 64 mm is R48
100% R64, comes closer to that blue/red example.

[Frits Overmars]

What about those 75%, I did not read any reply on that. 75% can't be good !
Would you mind telling us why 75% can't be good Henk?
Much to round and besides it does't look at all to the rouding of that blue and red example.
Peewee makes the drawing just right 75% of 64 mm is R48. 100% R64, comes closer to that blue/red example.If I understand you correctly, you say it can't be good because it doesn't look good. I think Peewee deserves a more substantiated reaction.

im trying to make a paper template of the exh roof then cut it out to mark the bore for grinding but its looking more arched than i thought. i used what frits posted. 75% bore is center radius. maybe i bungled it somehow. but see the photo to be sure.The port roof center radius of 75% of the bore is valid for a port width of 70% of the bore. For a 64 mm bore that means a port width of 44,8 mm, not 45,5 mm, and certainly not 51 mm, as shown in your drawing.
The FOS port shape concept was developed for port designing, not for template drawing. If you stretch chord widths to arc lengths, everything is pulled out of proportion and the radius percentages no longer apply.

In order to help Peewee out I briefly considered extending my port shape concept to be suitable for creating templates. But firstly, it's not really that simple, and secondly, I don't want to encourage the use of templates, not paper ones anyway. I never used one. At the end of the day you still have to work with the chord width of the port.

[TZ350]

2Stroke Stuffing.

<iframe width="560" height="315" src="https://www.youtube.com/embed/o8tlhSVDphE" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

<yt-formatted-string force-default-style="" class="style-scope ytd-video-primary-info-renderer" style="word-break: break-word;">Supercharged 50cc is Alive! Angry, Spitting Flames!

</yt-formatted-string>Looks like Alex has put the rotary exhaust valve project aside for the moment and has moved onto supercharging a more conventional 50.

[HenkS]

If I understand you correctly, you say it can't be good because it doesn't look good. I think Peewee deserves a more substantiated reaction.
The port roof center radius of 75% of the bore is valid for a port width of 70% of the bore. For a 64 mm bore that means a port width of 44,8 mm, not 45,5 mm, and certainly not 51 mm, as shown in your drawing.
The FOS port shape concept was developed for port designing, not for template drawing. If you stretch chord widths to arc lengths, everything is pulled out of proportion and the radius percentages no longer apply.

In order to help Peewee out I briefly considered extending my port shape concept to be suitable for creating templates. But firstly, it's not really that simple, and secondly, I don't want to encourage the use of templates, not paper ones anyway. I never used one. At the end of the day you still have to work with the chord width of the port.

Peewee, my translation of this answer is a little simpler,
Because everyone works like you with portmaps, so change that 75% as I wrote earlier to 100% and the problem is solved.
You actually see it quite easily, but if you calculate it, then that 100% is within 1% deviation. And that counts for every bore.
And mm to top of cilinder don't change between portmap and cordural .

[wobbly]

Husa , I have to disagree about bike tyre width not generating more grip , based purely on actual experience.
The Frepin TZ400 I built for Denis originally had a rear soft treaded 110/18 Avon as mandated by Post Classic Junior rules.
Later the swingarm was changed and an Avon AM23 soft 130/18 special construction rear was fitted , specifically designed to fit on the now way to narrow rim.
This generated so much rear grip the whole front end geometry , and the front tyre changed from a 90 to a 110 to get it to steer , and it dropped the Junior lap record at Hampton by nearly 2 secs.

Then the Aprilia Cup Bike with a RZ400 for Superlight in it , originally had a soft 150/17 rear tyre , this was changed to a soft 180/17 and again it needed huge changes in geometry to balance the grip levels.
Sure there will have been differing carcass construction etc , but absolutely the wider rear tyre generated way more corner grip, and it to broke the lap records at Hampton and Ruapuna.

[peewee]

Peewee, my translation of this answer is a little simpler,
Because everyone works like you with portmaps, so change that 75% as I wrote earlier to 100% and the problem is solved.
You actually see it quite easily, but if you calculate it, then that 100% is within 1% deviation. And that counts for every bore.
And mm to top of cilinder don't change between portmap and cordural .

thnks henk i like a simple answer :clap:

[husaberg]

Husa , I have to disagree about bike tyre width not generating more grip , based purely on actual experience.
The Frepin TZ400 I built for Denis originally had a rear soft treaded 110/18 Avon as mandated by Post Classic Junior rules.
Later the swingarm was changed and an Avon AM23 soft 130/18 special construction rear was fitted , specifically designed to fit on the now way to narrow rim.
This generated so much rear grip the whole front end geometry , and the front tyre changed from a 90 to a 110 to get it to steer , and it dropped the Junior lap record at Hampton by nearly 2 secs.

Then the Aprilia Cup Bike with a RZ400 for Superlight in it , originally had a soft 150/17 rear tyre , this was changed to a soft 180/17 and again it needed huge changes in geometry to balance the grip levels.
Sure there will have been differing carcass construction etc , but absolutely the wider rear tyre generated way more corner grip, and it to broke the lap records at Hampton and Ruapuna.

Hi I am not sure i said that?
Was that something Kevin Said or in the question to Kevin?
i thought Kevin said pretty much what you had said? which was what i said rather clumsily
I said the simple physic's of the sliding object in an equation doesn't take into account all the variables or words to that effect.

[F5 Dave]

Great so we are back to where we hopefully started. Friction is all very well, but rubber in shear deforms as it tries to smear itself on the concrete, if only just a little, and bites into all the little irregularities.

[TZ350]

2Stroke Stuffing.

351629

Ever more promising. I am looking forward to seeing some data from a couple of good runs with the supercharged setup.

<iframe width="560" height="315" src="https://www.youtube.com/embed/D_hLiEN3lK0" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

[ken seeber]

OK fellas, feel rewarded.

Give yourselves a pat on the back for all those tuning tips, STAs, RADs, exhaust temps, port staggers, jetting etc etc that you have been giving to Wobbly over the years. :killingme:killingme

Look closely at the pic.

351630

[lodgernz]

OK fellas, feel rewarded.

Give yourselves a pat on the back for all those tuning tips, STAs, RADs, exhaust temps, port staggers, jetting etc etc that you have been giving to Wobbly over the years. :killingme:killingme

Look closely at the pic.

351630

I manned the recovery quad on the qualifying day, and those guys were just flying. Well done Wobbly!

[wobbly]

Thanks Ken and Lodger , the guy in 3rd place has a Wobbly sticker as well.
The author forgot to mention Mat is a 10 times National Champ , getting the double digit was the goal in the weekend.
He isnt as old nor as good looking as me , but 2 little kids and a business taking over much of my engine building work probably means he wont contest any more - sad really as he is one
of the best kart peddlers I have ever seen or tuned for.

Edit , be real interesting the see what happens this weekend at the World Cup in LeMans , the factory TM will have some of the new homologation legal parts on board that next years KZ R2 will have.

[HenkS]

thnks henk i like a simple answer :clap:

Unnecessarily complicating is also a way.
The red/blue example is very misleading, because nowhere does it say that the 75% cordural should be measured.
Everyone I meet on the internet works with portmaps and applies that 75% to a portmaps.
And mm to the top of the cylinder are therefore also the best to check, so certainly templates are possible.

And not unimportant to know that that 75/100% is also just an approximation.
I have seen successful examples that had a radius of over 200% and were also wider than that 70% and had still not suffered any damage after years. Good gate edge rounding is a condition here.

[wobbly]

Frits makes the assumption we all know the measurements are chordal , its like trying to convince a cop the 100 sign on the side of the road you thought were mph as opposed to kmh.
And he has tried to give a guide for all bore sizes , we all know small bores down at 40mm are a special case and will tolerate more than 70% with ease , but anything with R200 and more than 70% would have
to have huge corner rads , but then its already well departed from anything approaching the mechanically possible " optimal " Blowdown geometry.

[HenkS]

Frits makes the assumption we all know the measurements are chordal , its like trying to convince a cop the 100 sign on the side of the road you thought were mph as opposed to kmh.
And he has tried to give a guide for all bore sizes , we all know small bores down at 40mm are a special case and will tolerate more than 70% with ease , but anything with R200 and more than 70% would have
to have huge corner rads , but then its already well departed from anything approaching the mechanically possible " optimal " Blowdown geometry.

Cordurally measuring the width is logical and easy to do. But how are you going to measure the top and bottom radius cordurally in the cylinder?
MM's from the top are no different than from a port folder, so how are you going to do that cordural in practice?

[Condyn]

Here is a paper port map of my cylinder. ( it looks a lot better in the bore ) haha.

75.4% chordal width exhaust port with small top corner radii. By the way I have 30 dyno pulls and 28 passes on the engine. I checked on the rings after 20 passes and re-ringed since I was in there. Rings showed very little wear ( but wear non the less ) Where they were being forced back into the bore. Also very very slight wear, where the end gap slides over the B port edge. ( really need to move the pegs )

I cannot wait to try the optimum shaped 70% port. If it produces the same power or more, we will happily go that route!

[wobbly]

The engines I work on with 54 bore have a 72.3 % chordal width , as the factory has a thing about pin plugs so I cant use 100% on the Aux.
To make repeatable , reliable ports , dead on bore centerline imho is impossible by hand , with or without a paper template or a lasercut pattern on a stick , especially when dealing with a raw casting.

Thus the ducts first 20mm ( just past the 3 port bridge ends ) is CNC cut in a Rottler 6 axis running software designed for 4T port machining with a ball - on - a - stick cutter.
The port/duct is designed as a surface in SolidWorks or NX and the tool path generated in PortExpert.

Many cylinders are junked as material shrinkage is not consistent , and one of the bridges can end up too thin - doing this by hand , the port may well end up exactly the correct shape , but
would then be asymmetric in the bore , and this is not reliable @ 72% - been there , and cut the engine in 1/2 with a broken rod.
The asymmetry pushes the ring sideways in its groove as well as inward , and the ring pin gets bashed on every stroke - quite a few at 14800.

Maybe not a viable option for a Bucket , unless you have a sponsor that sells alot of weed , but vital use of what is now common technology when living on the edge and pushing to the absolute max.

[Condyn]

And then the plater who smokes said weed goes and ruins everything anyway.

[wobbly]

Dead correct , I have to send 3 emails , write on the cylinder and put a note in the box - NO CHAMFERS OR A BBC WILL BE PLACED WHERE THE SUN DOESNT SHINE.

[ken seeber]

The author forgot to mention Mat is a 10 times National Champ , getting the double digit was the goal in the weekend.


The full(er) story.

https://www.kartsportnews.com/2022/08/30/10th-nz-national-title-for-kinsman/

[Frits Overmars]

To make repeatable , reliable ports , dead on bore centerline imho is impossible by hand , with or without a paper template or a lasercut pattern on a stick , especially when dealing with a raw casting.
Maybe not a viable option for a Bucket .... but vital use of what is now common technology when living on the edge and pushing to the absolute max.You said it Wob. I did not develop my port concept for Buckets, but I did make it available for Buckets, for everyone to use it as they see fit.


I have to send 3 emails , write on the cylinder and put a note in the box - NO CHAMFERS OR A BBC WILL BE PLACED WHERE THE SUN DOESNT SHINE.I don't quite understand how the presence of the British Broadcasting Corporation would make a difference; I'd rather escort my cylinders with a loaded rifle.
Jan Thiel once considered bringing a pack of Pit Bulls with Aids to the plater's, but then he has always been famous for his creative ideas :msn-wink:.

[lohring]

My simple minded porting templates for small, industrial type race engines is described below. Those engines have one piece cylinders with included heads so it's difficult to use port to head measurements otherwise. Maybe something similar would be helpful in larger engines.

Lohring Miller

351643

[wobbly]

Ken and I were discussing transfer port flow regimes and he asked me to screenshot the Mass Flow Rate of a TM KZ R1 at peak power ( 13750 ).
This is the A port ( 1st to open ) , note the reverse flow down the duct at TPO and TPC due to a positive Blowdown pressure ratio , then a negative pressure ratio in the case.

[Grumph]

I don't quite understand how the presence of the British Broadcasting Corporation would make a difference; I'd rather escort my cylinders with a loaded rifle.
Jan Thiel once considered bringing a pack of Rottweilers with Aids to the plater's, but then he has always been famous for his creative ideas :msn-wink:.

I've met the guys Wob sends his cylinders to. Nice guys, catch on quickly. Wob's stuff they understand - but they wanted to know if I knew Neil Hintz as his stuff was just plain weird. I think I reassured them. BBC = Big block Chevy. Don't know if that idiom translates into Dutch.

[wobbly]

Here is what I didn't expect , as I have never used the Mass Flow data metric in EngMod to investigate previously.
At 10,000 rpm , the low end of the used power band on track , there is no flow reversion from an excess Blowdown delta across the port face.
But there is huge back flow as the port is closing due to the case going negative.
I knew the inlet flow from the reeds begins at about TPC , as I did tests years ago cutting away the piston inlet side skirt , thinking it was impeding the flow into the case from the reed box.
But it doesn't , as the piston is well on its way up the bore when the reeds start flowing into the case.

No free lunch there sadly - but it makes me think that a large amount of Desaxe cylinder offset may be something to investigate again .
As in one direction of offset the timing asymmetry generated by this technique , causes late opening and early closing of the ports.
This may need the Exhaust timing increased to keep that side of the equation working correctly with the pipe TL.

[Flettner]

Or open the inlet port 30 degrees ABDC. Rotary Disc Valve.
But only in the power band, below those revs, port opens after transfers close. Sliding Gib tech. Perhaps?
Thats how my 360 is setup. Reeds are for wetlands.

[wobbly]

Yea I know Neil , but I am trying to win World Titles in Karting , not throw dirt in the face of a following rider in Vintage MX.
Both are worthy pursuits , but one uses up funds , the other is gona buy me an Aston Martin - fuck the tree huggers - with a BBC.

[Frits Overmars]

Here is what I didn't expect , as I have never used the Mass Flow data metric in EngMod to investigate previously.
At 10,000 rpm , the low end of the used power band on track , there is no flow reversion from an excess Blowdown delta across the port face.
But there is huge back flow as the port is closing due to the case going negative.
I knew the inlet flow from the reeds begins at about TPC , as I did tests years ago cutting away the piston inlet side skirt , thinking it was impeding the flow into the case from the reed box.
But it doesn't , as the piston is well on its way up the bore when the reeds start flowing into the case.That's Herr Helmholtz messing up things for you, Wob. https://en.wikipedia.org/wiki/Helmholtz_resonance
The cycle from a positive crankcase pressure differential accelerating the transfer flow to a negative case differential slowing that flow velocity back to zero again takes a fixed amount of time. At low revs this time is less than the total transfer opening time, so the cycle continues, performing more than half a sine wave during the open transfer period.
It's the same phenomenon you can observe with piston-controlled inlet systems, where at low revs blowback can occur although the piston is still on its way up towards TDC, so the crankcase pump is still trying to inhale.

In theory the reed valve inlet system ought to prevent the crankcase pressure from dropping below atmospheric. In practice the reed valve needs this pressure drop before it will even think about going to work.
Neils gibs-controlled rotary inlet system offers the best of both worlds. Although.... you may remember Roland Holzners 24/7 experiment at Modena a couple of years ago. Roland realized it without any electronics because the CIK would have vetoed that. His system worked, but with the karting world being the karting world, the CIK vetoed it anyway, like it had done with Rolands synthetic inlet inserts some time before. If the CIK doesn't like you, they'll let you know...


No free lunch there sadly - but it makes me think that a large amount of Desaxe cylinder offset may be something to investigate again .
As in one direction of offset the timing asymmetry generated by this technique, causes late opening and early closing of the ports.
Not even a free breakfast, I'm afraid. The problem is not the symmetry of the port timing; it's the duration of the timing. Asymmetry might have worked in the long-gone era of tiny crankcase volumes but these days Helmholtz will hardly be impressed by what the piston happens to be doing.

[HenkS]

You said it Wob. I did not develop my port concept for Buckets, but I did make it available for Buckets, for everyone to use it as they see fit.




Not being able to answer the question is correct, only possible in CNC for the few who can.
But they are not waiting for such a simple drawing.
And for the amateurs who are the real target group here, be misled !!
As can be clearly seen in this example, because they can only work with portmaps.

Thank you on behalf of all "Buckets"
What an arrogance !

[jonny quest]

Looking for pipe specs mid 90s Honda CR250R for motocross use.
Anyone have anything they can share please?

[andreas]

YZ 250 pipes -06, perhaps they can serve as a guideline. ( Outside diameter)

[JanBros]

And for the amateurs who are the real target group here, be misled !!
As can be clearly seen in this example, because they can only work with portmaps.

Thank you on behalf of all "Buckets"
What an arrogance !

Foekema ? Is it you Luc ? catfishing again ?

[wobbly]

For someone to be derogatory of Frits as being arrogant , is easily explained by the old adage " that which you despise in others , is within yourself ".
HenkS may not be NoLuc , but for sure its one of his relatives.

But if that is the case , then fuck off with your delusions somewhere else.
Been banned once, its easy to make it happen again.

You have spoiled the weekend of a Dutchman winning at Zandvoort.

[TZ350]

.
Buckets, it's like a happy dinner party.

351660

HenkS we are all friends here because we bring positivity to the table, you are invited.

[husaberg]

HenkS we are all friends here because we bring positivity to the table, you are invited.

Hi Rob HenkS/LucF has been goneburered again, It appears that whilst he was leaving, he also tripped down the stairs and beat himself up with a phonebook.:whistle:
He apparently gave no forwarding address.....
Its a shame, he could have just changed his user name to Smeerlap Zakkenwasser.

[ceci]

Although.... you may remember Roland Holzners 24/7 experiment at Modena a couple of years ago. Roland realized it without any electronics because the CIK would have vetoed that. His system worked, but with the karting world being the karting world, the CIK vetoed it anyway, like it had done with Rolands synthetic inlet inserts some time before. If the CIK doesn't like you, they'll let you know...



1º I am glad of the success of Roland Holzner in Modena with the 24/7 valve, he has succeeded where HIROSE TATEO did not in SUZUKI MOTOR CO from 1983 to 1986.
2º I regret that the CIK is against progress, it is unfair to reject all progress

[ken seeber]

2º I regret that the CIK is against progress, it is unfair to reject all progress

Ceci,

Things are not so bad with the CIK and progress continues:

"It is now ok to paint the outside of the cylinder casting any colour, except blue and red combined"

[Frits Overmars]

.
Buckets, it's like a happy dinner party.
351660Thank you guys, you make me feel welcome and secure :niceone:

[Vortex]

Not being able to answer the question is correct, only possible in CNC for the few who can.
But they are not waiting for such a simple drawing.
And for the amateurs who are the real target group here, be misled !!
As can be clearly seen in this example, because they can only work with portmaps.

Thank you on behalf of all "Buckets"
What an arrogance !

Well, Mr HenkS,
I can hardly hold back now. I read everything here and learned a lot. I hardly never comment because I try to be modest towards the experts whom I consider better than myself. You should be glad that Frits and Wobbly except to share their knowledge with all of us. You should calm down again very quickly, because your statement is absolutely out of place. :angry:

[Javi]

Always positive,Mr Frits.Much encouragement to all.There are many of us who follow you.
Thanks to all.

[ceci]

Always positive,Mr Frits.Much encouragement to all.There are many of us who follow you.
In my land,that guy has a name,he's called a cobarde hijo de puta.

I have no sympathy for Luc Foekema.
I have never supported foekema in any publication.
You can be direct, but don't let others down "they will think that we are all just as direct"
That's why it doesn't take away to have good manners
And not have ugly words

[wobbly]

The template scenario for the Exhaust is I believe best implemented with a metal pattern , this can also have an added register plate welded to it to fix the top of cylinder positioning.
Any laser company will have the software to generate the shape from your chordal sketch , but free CAD software is easily obtained as well.
In any case the chordal shape will need to be used in a port analysis program , everyone here has access to these , whether a spreadsheet or something like EngMod.

I try to keep my written barbs under control , and rarely become abusive on here , but NoLuc instantly brings out the daggers - as his modus operandi has always been to display his
narcissistic personality disorder and tell us absolutely nothing of any use.

Im really fizzing at the bung right now ,as the months of work I put in paid off with a 1st/3rd podium at the Worlds in LeMans , so as Ken said , thanks everyone for the help.

[dtenney]

Modena tried to utilize the 24/7 reed valve in it's KZ motor. Do we have an understanding of how effective it was? Any insights are much appreciated.

[ceci]

Ceci,

Things are not so bad with the CIK and progress continues:

"It is now ok to paint the outside of the cylinder casting any colour, except blue and red combined"

Hi Ken

It is only a suggestion, since the CIK prohibits the use of electronics and makes it difficult to use the valve 24/7 by not being able to use servomotors.
A pneumatic actuation mechanism similar to the one that activates the RAVE valve could be used (it would be actuated with the pressure of the exhaust gases) and since the activation mechanism and the 24/7 valve are separated, we would need a hydraulic transmission mechanism to activate it.
It can be simpler than the mechanical cam mechanism on the crankshaft and efficient since when the carburetor is closed the engine does not drop rpm immediately.

[F5 Dave]

Well this is cute, fast forward it a bit, and catch the end as well
Transparent cylinder head.
https://www.youtube.com/watch?v=K9U_QyfJ19A

[ken seeber]

Hi Ken

It is only a suggestion, since the CIK prohibits the use of electronics and makes it difficult to use the valve 24/7 by not being able to use servomotors.
A pneumatic actuation mechanism similar to the one that activates the RAVE valve could be used (it would be actuated with the pressure of the exhaust gases) and since the activation mechanism and the 24/7 valve are separated, we would need a hydraulic transmission mechanism to activate it.
It can be simpler than the mechanical cam mechanism on the crankshaft and efficient since when the carburetor is closed the engine does not drop rpm immediately.

Ceci, as Frits pointed out, the CIK is the CIK and they have their close mates.

That same Frits, quite some time ago, did make comment on the 24/7 Modena system, but can't remember if he reported on any useful gains, understandable at the time cos it was just new.

However, I'd be ever so happy to hear if it did offer usefulness. The problem then, irrespective of some snazzy gizmo one can come up with and even if it is withing the current rules, is that the CIK might immediately outlaw it, thereby wasting a lot of resources in its development and the frustration.

Seems that the only freedom left is just the CC capacity limits of the Freetech 50 and Bonneville classes.

[dtenney]

Outboard hydro classes are for the most part only restricted by bore and stroke.

[Peter1962]

Ceci, as Frits pointed out, the CIK is the CIK and they have their close mates.

That same Frits, quite some time ago, did make comment on the 24/7 Modena system, but can't remember if he reported on any useful gains, understandable at the time cos it was just new.

However, I'd be ever so happy to hear if it did offer usefulness. The problem then, irrespective of some snazzy gizmo one can come up with and even if it is withing the current rules, is that the CIK might immediately outlaw it, thereby wasting a lot of resources in its development and the frustration.

Seems that the only freedom left is just the CC capacity limits of the Freetech 50 and Bonneville classes.


If I remember correctly, Frits said that Roland Holzer found an increase in HP of about 10% . And that Roland Holzer no longer works for Modena. So probably no more news to be expected...


But... a couple of days ago wobbly said that he gets the opportunity to experiment on behalf of a KZ engine constructor on his ideas for future development on two stroke engines. (like raising the floor of the exhaust, or his specific design for cooling only the squish zone in the combustion chamber). Maybe some experiments with a 24/7 valve could be included ? :wings:

[Peter1962]

Outboard hydro classes are for the most part only restricted by bore and stroke.

Yes, but those engines can thus also use rotary discs, which are superior to reed valve systems. (proof of concept : all the world titels obtained with Jan Thiel his engines)

[Frits Overmars]

If I remember correctly, Frits said that Roland Holzer found an increase in HP of about 10% . And that Roland Holzer no longer works for Modena. So probably no more news to be expected...
But... a couple of days ago wobbly said that he gets the opportunity to experiment on behalf of a KZ engine constructor on his ideas for future development on two stroke engines. (like raising the floor of the exhaust, or his specific design for cooling only the squish zone in the combustion chamber). Maybe some experiments with a 24/7 valve could be included ? :wings:This KZ engine constructor who is eager to get Wobbly on board, is not Modena. Or rather, Modena may be eager, as may be more than one other KZ constructor, but they are not in the picture. And anyway, no kart constructor can afford to finance experiments of which they know in advance that they won't be allowed to use the results in practice.

[ceci]

It is an injustice that they prohibit the evolution of the two stroke engine,

https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=351667&d=1662571727


The information that you can find in this forum about the 24/7 valve is that it is harmed by not being able to use the "servomotor" electronics, and having to use an inertia mechanism.

https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=331769&d=1499941687

It is useless, but I show you in 2D drawing the suggestion "it is always easier to understand".

[wobbly]

The CIK banned power valves and any associated actuating mechanisms in KZ, so using an inertia drive to operate a 24/7 is doomed.
Spring loaded petal plates cleverly gets around the rule , but they banned it anyway , as being clever is only allowed when its not obvious or " in your face ".
The pipe is the most worthwhile area of development , and this is what I concentrated on , but then its homologated for 3 years and everyone gets to see the dimensional cleverness.
Helps other manufacturers , but not me , as apparently Vortex cannot beat my TM R1 pipe on their engine , so they are simply stealing the design for their next years homologation.

Ports , reed petals , cooling , superfinishing , etc are free as long as the hardware " looks " like the homologation pictures.
Thus for example moving the water inlet on a cylinder from the side , to the back , is frowned upon as its not visually the same.
But if the water is run thru channels from between the crankcase/gearbox , over the mains , and up each side of the boost port , and this is shown in the papers , its legal.
Now , if it cant be seen its fine as well , except of course you have water holes thru the case deck/ cylinder face in the wrong place - bugger.

[wobbly]

To see what the results would be if using the FOS correction factor I had it put into a spreadsheet.
The issue is that when using standard air at 20*C , 50% , 1013.5mBar it shows a correction of 1.125 ie +12.5%
This may well be correct if the math has been transcribed properly ?

[Frits Overmars]

To see what the results would be if using the FOS correction factor I had it put into a spreadsheet.
The issue is that when using standard air at 20*C , 50% , 1013.5mBar it shows a correction of 1.125 ie +12.5%
This may well be correct if the math has been transcribed properly ?For all I can see the math has been transcribed properly but apparently spreadsheets are like dyno power curves: you can't trust them unless you've forged them yourself.
Here are your version, and mine in blue.
351688
I wonder what could possibly go wrong with this simplest of equations. Maybe your spreadsheet doesn't understand that 1^x = 1 whatever x is ?

[Vannik]

For all I can see the math has been transcribed properly but apparently spreadsheets are like dyno power curves: you can't trust them unless you've forged them yourself.
Here are your version, and mine in blue.
351688
I wonder what could possibly go wrong with this simplest of equations. Maybe your spreadsheet doesn't understand that 1^x = 1 whatever x is ?

Is it not maybe the decimal delimiter in Excel? Depending on setup it can be either a comma (typical European) or a point (most of the rest of the world)? I have burnt my fingers a few times on this.

[wobbly]

Thanks Frits , none are so blind as those that cannot see.

[karter444]

Hi
Is there anyone in New Zealand that can successfully change the position of a piston ring locating pin ,
cheers Richard

[husaberg]

Hi
Is there anyone in New Zealand that can successfully change the position of a piston ring locating pin ,
cheers Richard

Pretty sure Rob (tz350)detailed it in here use piano wire as a search.
i watched by father do it once he did it with a brass screw or stud.

https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130986619&highlight=piano+wire#post1130986619

I use a 1.5mm dia needle roller from a little end bearing . Material is tough and also polished so there is no fretting on the ends of the ring. Drill down from the top of the piston allowing for some interference fit (say .05mm ) so the end of the pin is 1 - 1.5mm below top of piston, then weld over the hole to prevent the pin from coming out. You may get a slight swelling of the piston diameter at the position of the pin. Dress this off carefully with a mill-cut file. With a two ring piston you will have the ring gap in the same spot for both rings but this is fine.

https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1131077307&highlight=piano+wire#post1131077307

This thread is best read backwards, that way you get to the good stuff first. Page's 500, 1000 and 1500 are worth a visit.

And there are thousands of pictures you can look through if you use the thread tools.

What went wrong, poor workmanship and the retaining tip of stainless wire I used fractured from vibration.

If I was to try again I would use the Yamaha racing TZ approach of drilling down from the top and piano wire with the tip bent over in the hole. Piano wire wont fracture like the SS did.

334094

Emess posted a very helpful tip for searching this or any other thread.


Some old TZ pistons and someone who may or maynot be Ago

257747257748257749

To replicate the TZ pistons use Piano wire sharpened on the end for the pin, Piano wire can be bent so it stays in place.

https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130260669&highlight=piano+wire#post1130260669



When moving ring pins I simply use a small riffler file and shave down the old pin flush with the back of the groove.
You could of course use a 1mm slot drill in the mill.
The new pin is easily made from whats called piano wire, and use the Z axis hand wheel after drilling the hole 0.05mm undersize to press the wire in.
Never had a failure as I have always been moving to 6 o"clock.

Ken Seeber of course might have an idea how to do it professional like as well:innocent:

[wobbly]

For those of you using SportDevices dyno software I have got them to add FOS 2Stroke Correction capability.
I wont get a chance to run an engine with differing weather until next week , but I can already see that it has a much more realistic amount of correction for values that
depart alot from Std Air than the J or SAE algorithms used previously.

Next addition I have asked for is RAD/Density Altitude to be added to the available metrics outputs , so its easy to begin constructing jet charts based on best power egt /weather data.
Simple " Air Density " is of no use for tuning , that I know of anyway.
Cheers big time Frits.

Edit - Shit it just occurred to me I should have asked permission before requesting this to be included into a commercial product - my apologies Frits.


http://sportdevices.com/sportdyno41-whats-new.php
http://sportdevices.com/download/sportdyno41.61.msi

[F5 Dave]

Interesting read thank you, things I hadn't considered, not that I'm intending on trying. Just one typo I noticed on 'liter' and I only mention it in the best intentions, I have only one language and can't imagine how it must be with spelling.

Thanks again.

[Frits Overmars]

Interesting read thank you, things I hadn't considered, not that I'm intending on trying. Just one typo I noticed on 'liter' and I only mention it in the best intentions, I have only one language and can't imagine how it must be with spelling.
Thanks again.I am grateful for your remark Dave. I checked again and I noticed that it depends on the settings of the translation program.
If I choose British English, it should be litres and if I choose American English, it should be liters.
I'm going to choose liters now, which looks more natural to me anyway because it's the same as in my native language.

EDIT: I can't seem to substitute the PDF in my previous post, so I am going to delete the whole post and re-post it below with the corrected PDF.

[Frits Overmars]

For those of you using SportDevices dyno software I have got them to add FOS 2Stroke Correction capability.
I wont get a chance to run an engine with differing weather until next week , but I can already see that it has a much more realistic amount of correction for values that depart alot from Std Air than the J or SAE algorithms used previously.
Next addition I have asked for is RAD/Density Altitude to be added to the available metrics outputs , so its easy to begin constructing jet charts based on best power egt /weather data. Simple " Air Density " is of no use for tuning , that I know of anyway.
Cheers big time Frits.
Edit - Shit it just occurred to me I should have asked permission before requesting this to be included into a commercial product - my apologies Frits.No worries Wob, I feel flattered. And there's nothing that cannot be made up with a bottle of high-octane booze :drinkup:

Speaking of which, I finally found the time to prepare an English version of my Petrol-Ethanol-Methanol-E85 treatise. Here it is.
351698351704351705

[ken seeber]

Pretty sure Rob (tz350)detailed it in here use piano wire as a search.
i watched by father do it once he did it with a brass screw or stud.

Ken Seeber of course might have an idea how to do it professional like as well:innocent:

Hewsar, I'm not a pro :laugh:...shifting the AR pin is not something we do. However, there some thoughts:

Firstly removing the old pin. As Wobbly suggests, it can be filed away, but absolute care must be taken to ensure that the sealing face of the groove is not damaged. One could fit a shim between the bottom of the groove and the file to prevent any contact. Another option could be to mill/drill the back section of the (usual) boss cast in the inside of the piston. This could expose the inner end of the pin which then could be pressed inwards such that its end was below the bottom of the ring groove in the piston. Another option could be to spark erode the pin away.

OK, the old pin is now out of the way, so a new pin is required. This can be done horizontally (or near so) or vertically. This suits most flat (rail) rings where there is a top land. The AR pin is positioned such that it doesn’t break thru the sealing face of the ring groove. We use pins of around 8 long * Ø1.5 , slightly tapered on one end with a longitudinal slot to prevent possible hydraulic locking should there be any coolant etc in the hole when pressing in. Interference is around 0.05. Obviously it must be pressed in far enough to provide an adequate clearance behind the ears at the ring gap. Suitable pins could be easily made from piano wire.

351700

Vertical pins are pushed down from the crown, and in the case of the early Yamaha KT100S piston around Ø1.0, far enough to enter a small shallow drilling in which the end of the pin is slightly bent over to prevent it escaping.

351701

However for Dykes rings, which are essentially flush with the line of the crown shape, many are angled slightly downward to minimise the chance of the pin cracking the top of the crown because the pin is so close to the crown surface.


If you want to be really, really, really crude, (obviously not an Australian idea) one could notch out original (steel) ring so the gap is shifted to be in a blank area of the bore. Certainly not recommended for a CI ring. Let us know how that one goes.

351699

[Frits Overmars]

351700
I came across pins like these in Elko pistons, fitted by Rotax in the late 1970s. They caused terrible detonation. With massive pins the deto was completely gone.


Vertical pins are pushed down from the crown, and in the case of the early Yamaha KT100S piston around Ø1.0, far enough to enter a small shallow drilling in which the end of the pin is slightly bent over to prevent it escaping.

351701
I know this scheme worked for Yamaha but it didn't work for us. Unless the bore between the ring groove and the 'shallow drilling' is really, really long, bending the pin's lower end will hurt the press fit of the pin in the bore enough so that it will eventually work loose and wreck havoc. Our solution was to close the top end of the pin bore by welding.

[karter444]

Hewsar, I'm not a pro :laugh:...shifting the AR pin is not something we do. However, there some thoughts:

Firstly removing the old pin. As Wobbly suggests, it can be filed away, but absolute care must be taken to ensure that the sealing face of the groove is not damaged. One could fit a shim between the bottom of the groove and the file to prevent any contact. Another option could be to mill/drill the back section of the (usual) boss cast in the inside of the piston. This could expose the inner end of the pin which then could be pressed inwards such that its end was below the bottom of the ring groove in the piston. Another option could be to spark erode the pin away.

OK, the old pin is now out of the way, so a new pin is required. This can be done horizontally (or near so) or vertically. This suits most flat (rail) rings where there is a top land. The AR pin is positioned such that it doesn’t break thru the sealing face of the ring groove. We use pins of around 8 long * Ø1.5 , slightly tapered on one end with a longitudinal slot to prevent possible hydraulic locking should there be any coolant etc in the hole when pressing in. Interference is around 0.05. Obviously it must be pressed in far enough to provide an adequate clearance behind the ears at the ring gap. Suitable pins could be easily made from piano wire.

351700

Vertical pins are pushed down from the crown, and in the case of the early Yamaha KT100S piston around Ø1.0, far enough to enter a small shallow drilling in which the end of the pin is slightly bent over to prevent it escaping.

351701

However for Dykes rings, which are essentially flush with the line of the crown shape, many are angled slightly downward to minimise the chance of the pin cracking the top of the crown because the pin is so close to the crown surface.


If you want to be really, really, really crude, (obviously not an Australian idea) one could notch out original (steel) ring so the gap is shifted to be in a blank area of the bore. Certainly not recommended for a CI ring. Let us know how that one goes.

351699


Thanks for the info Ken , I have replied to your email
cheers Richard

[husaberg]

from a few pages ago about grip
https://suspensionsecrets.co.uk/tyre-performance-and-grip-a-deeper-look/

[andreas]

Great Husa

[Condyn]

I am looking for a two stroke oriented cad/cam person in the states that I can easily send sample parts back and forth. If this is you, drop me a message.

[Javier Ruda]

Hi, I’m about to buy a single ring piston, maybe wossner maybe vertex. The wossner one has a blind hole on each side, around (b/c) a/b transfer ports.


No luck yet searching the posts. If anyone can tell me pros/cons I would be grateful.

[andreas]

The wossner is forged and the vertex is cast, thats probably a bigger difference than the "pockets", which I don't think do anything for performance.

[Javier Ruda]

The wossner is forged and the vertex is cast, thats probably a bigger difference than the "pockets", which I don't think do anything for performance.

Thank you andreas. I see that Vertex should run tighter clearance. Wossner is 0.05 mm and Vertex 0.03 mm I think. So if there is no performance gain, maybe cast is better, for having less themal expansion.

[andreas]

Cast has less thermal expansionand and usually cost less, while a forged piston is stronger.

[wobbly]

Pockets in the skirt always loose power.
Especially in a 3 port where the pocket adds to port linking between the A port and the Aux above it.
Back to back the new TM semi flat top with pockets in the skirts above the pin , looses between 0.5 and 0.75 Hp over a piston with exactly the same geometry
and no pockets.

And even without the Aux ports , the pockets suddenly add volume going over the transfers , this is part of the reason that pin plugs that fill the void thru the pin connecting to the transfer ports , add power when used.

Many of the Wossner forged pistons now have almost the same bore clearance as the cast versions.
0.03mm clearance is super tight , 0.05 is pretty usual for Wossners even in big piston sizes and high bmep applications.

[Javier Ruda]

Pockets in the skirt always loose power

Thank you wobbly. I will avoid pockets.

I did a search for recommended piston to wall clearance on rotax 125 cylinders:

1995 moto Aprilia RS125
0.020-0.035mm

2000 kart Rotax FR 125 Max
0.025-0.050 mm

2001 kart Rotax 125 Max Evo
0.04-0.05 mm

2021 kart Rotax 125 Max DD2 Evo
0.05 mm

And I remember now that I fitted the kart thermostat 45°C instead of the original Aprilia 70°C. Put all together, I think I will use 0.04 mm and avoid the super tight 0.03 mm.

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/Kq0_iA7py40" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[Frits Overmars]

I did a search for recommended piston to wall clearance on rotax 125 cylinders:

1995 moto Aprilia RS125
0.020-0.035mm

2000 kart Rotax FR 125 Max
0.025-0.050 mm

2001 kart Rotax 125 Max Evo
0.04-0.05 mm

2021 kart Rotax 125 Max DD2 Evo
0.05 mm

There is one detail missing in those recommendations: the number of seizures.
Aprilia must have made a fortune selling cylinders and pistons in 1995....

[Condyn]

With a 69.5mm bore and forged wiseizcos I use .0055”. This is because when the engine dyno operator gets out of a pull they sometimes stick if any tighter. Before we dyno tested everything, there was no issues at the track with tighter clearance.

[Javier Ruda]

There is one detail missing in those recommendations: the number of seizures.
Aprilia must have made a fortune selling cylinders and pistons in 1995....

:laugh: Indeed, these Aprilia numbers are way off compared to the others.

[Vortex]

There is one detail missing in those recommendations: the number of seizures.
Aprilia must have made a fortune selling cylinders and pistons in 1995....

I have the info that with that tight piston clearance (2/100mm) they had to heat up first the coolant liquid and the entire engine before they could even start the engine.
Hope my info is correct.

[wobbly]

Condyn the only time I have seen anything like 0.0055" used ( 0.1375mm ) is in hotrod jetskis , due to the very cold waterjacket temps used.
The fix is to use restrictor pills in the water dump tubes from the cylinder , or a thermostat to keep the water temp at a reasonably sane level.
If any race engine locks up when backing off a load , then that instantly red flags the tube/needle is way lean on less than WOT.
The Wossners in 72mm size for a CPI 485 Banshee I have built probably 20 of these, and they run forever at the factory recommended 0.06mm ( 0.0024" ).

[jamathi]

There is one detail missing in those recommendations: the number of seizures.
Aprilia must have made a fortune selling cylinders and pistons in 1995....

Aprilia made a fortune on selling pistons every year....
Piston clearance should be 0.04mm they said.
Out of curiosity I tested bigger clearances:
0.05mm gave MORE power.
And 0.06mm gave the same power as 0.04!
There were 'heavy' and 'light' pistons.
With the heavy ones you could do all practice sessions AND the race without power loss
The light ones had to be changed every day, they deformed and caused power loss...
I never understood the 'advantage' of the lighter pistons.
Except that more money was made on them.....
On the dyno I always used the heavy ones, without any problem!!!
Up to 30 power curves with the same piston, without any power loss!
About 80% profit was made on the pistons....

[jamathi]

The wossner is forged and the vertex is cast, thats probably a bigger difference than the "pockets", which I don't think do anything for performance.

The 'pockets' are mostly negative for power.
Cast pistons give slightly more power in my experience!

[Javier Ruda]

Out of curiosity I tested bigger clearances:
0.05mm gave MORE power.
And 0.06mm gave the same power as 0.04!

Thank you Jan! Then cast and 0.05 mm is the good try, and no pockets as andreas and wobbly said.

I have one more doubt, maybe silly. The cylinder is not new, so a bit ovalised, 0.006 mm. Does this make a difference?

[wobbly]

I diamond hone when I see 0.005mm , its always on the thrust face and each side on the bridges.
But the KZ engines run 0.07mm clearance to start with to reduce run in time ( thus extending crank life ) and there is no difference in power I can see between 0.07 and 0.09.
You can do it a couple of times and fit a new piston, then go up to the next size from 53,93 to 53 ,94.
If you dont hone it , then you see brown blowby just below the ring very quickly even with a new piston fitted.

Edit = 0.005 correction.

[Javier Ruda]

I diamond hone when I see 0.0005mm
If you dont hone it , then you see brown blowby just below the ring very quickly even with a new piston fitted.

Thank you wobbly! By the way, very impressed from that measurement.

[wobbly]

Sorry one to many 0s - 0.005

[Condyn]

Re- wobbly on the clearance.
I will take a closer look at the needle/tube, however this issue has only happened on the dyno and never at the track thus far with slightly tighter bores. Also I have never noticed anything that stands out on my data logger on shutdown.

We race in temperatures sometimes cresting -30c so I am sure that is why the manufacturer specs such a loose clearance. .004-.006” or .1-.15 mm is very common to see recommended in the snow application. Some oem cast pistons are specified a tighter clearance than that, however not very common. By no means am I saying the common practices that we have been using for decades are correct, they may very well be folklore. The risk, or imaginary risk of seizing at the track is just too great to tighten the clearance, especially after the dyno experiences.

[wobbly]

Yea I get it now - in the snow you have the same issue as the jetski"s except its the ambient air freezing everything.

[Flettner]

The 360 is up and running again with a new autolube system. Seems also the disc had shifted again, this is why it started to behave odd on the dyno, also becoming difficult to start. Disc drive system was only ever clamped in place but now is pinned. Sounds better, starts easier and apears to hold tune now. Pictured a squirrel fan for extra cooling, zippy tied on.
Maybe now some results to 'take home'.

[husaberg]

Building a BRC YZM500 2 stroke:niceone:


<iframe width="560" height="315" src="https://www.youtube.com/embed/7NA0sddkSq0" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>



<iframe width="560" height="315" src="https://www.youtube.com/embed/SMsCf9zKOJY" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Riley Will....
Congrad's thats a quality piece of kit i had seen some of the stuff a while back but a Balance shaft and modern chassis and Decomp pv and case reed.

[Flettner]

Something you dont see every day, a nitrous CR500. Because death cant come quick enough...... I guess😁.

[Henrik Y]

A little update on my gearbox swap. I've been riding it for a bit this summer and it seems to work just fine. Better overlap so I could push the powerband a little higher and current top speed which I've only tried once is almost 170km/h, could probably push a little more but I'll stop there for now as I'm happy with it and it performs well on the small country roads I ride with it. It's fast enough to get dangerous.


https://www.youtube.com/watch?v=p2rgN_Tjer4


https://www.youtube.com/watch?v=oM97zxLgNjI


https://www.youtube.com/watch?v=KaQXDVGolI8


So I cut the side of the engine case and widened it. Also had to widen the outer cover as well for the chain to clear the clutch cylinder and braced it to make it stiffer as it was flexing when clutching. The selector drum required most modification, had to resize one side, cut it in half and add a bit for the gear points or whatever you call it. It was a lot of fiddling back and forth but in the end it worked out pretty well. Had to correct some slight warping of the case as well after the welding.

351771
351772
351773
351774
351775
351776

[Henrik Y]

351777
351779

I built a new pipe for a little more peak and higher revs.
351778

And now I can bring my legs as well ;)
351780

Hope to get it painted next summer.

[Peter1962]

If I may ask : why did you choose to weld, and not use a spacer plate for widening the cases ?

[Henrik Y]

If I may ask : why did you choose to weld, and not use a spacer plate for widening the cases ?

Then you have to widen everything else. Frame, cylinder, crank and so on.

[wobbly]

After using the FOS 2T power correction algorithm in my latest dyno tests , that gives much more realistic power numbers ( for example high mBar ambient air - I had an unbelievable 1040 the other day )
I have discovered that JIS D1001 correction gives almost identical results.
This might be useful on dyno software where the FOS code cant be inputted.
Ive got no idea what the correction data is for this , but it does seem to be much closer than any of the others commonly available.

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/meIhw83RP-8" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

2Stroke Stuffing and a new direction with a new centrifugal blower.

[porttiming124]

After using the FOS 2T power correction algorithm in my latest dyno tests , that gives much more realistic power numbers ( for example high mBar ambient air - I had an unbelievable 1040 the other day )
I have discovered that JIS D1001 correction gives almost identical results.
This might be useful on dyno software where the FOS code cant be inputted.
Ive got no idea what the correction data is for this , but it does seem to be much closer than any of the others commonly available.


I'm happy to learn that the JIS correction is close to that of FOS because I asked Land and Sea (dyno) to integrate the FOS correction into my software and they don't seem to be interested. Thanks for sharing your tests.

[wobbly]

Man thats crap customer service from L&S , imagine the hundreds of their dynos that are 2T dedicated.

[Flettner]

360 ready for a ride, finally.
TPI mk2, E85 fuel, reverse rotation crank, sliding gib throttle / valve timing, reverse cylinder, double counter rotating balance weights, autolube direct to the bigend via an airstream, electronic guillotine type powervalve, water cooled crankcase, toridal head with an 8mm spark plug.
It goes pretty good around the yard.

[ken seeber]

360 ready for a ride, finally.
TPI mk2, E85 fuel, reverse rotation crank, sliding gib throttle / valve timing, reverse cylinder, double counter rotating balance weights, autolube direct to the bigend via an airstream, electronic guillotine type powervalve, water cooled crankcase, toridal head with an 8mm spark plug.
It goes pretty good around the yard.

Shorelee Fletto, you could have thought of some other things to add to the list........:scratch::scratch:

That aside, well done...

[Pursang]

Shorelee Fletto, you could have thought of some other things to add to the list........:scratch::scratch:

That aside, well done...

Fletto.....Well done!!

[Flettner]

Remind me, what was the BMEP of the Aprilla RSA 125?

[husaberg]

Remind me, what was the BMEP of the Aprilla RSA 125?

At around 53 or 54 the works Norton Manx had BMEP value of almost 14 bar or 200psi at 7000rpm
but to be fair they had nearly 4 times as long to fill the cylinder compared to to a 125 2T 14,000RPM

According to Frits for the Aprilia RSA125 the BMEP was 17 bar
http://www.pit-lane.biz/t117p820-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked

[Frits Overmars]

At around 53 or 54 the works Norton Manx had BMEP value of almost 14 bar or 200psi at 7000rpm
but to be fair they had nearly 4 times as long to fill the cylinder compared to to a 125 2T 14,000RPM
According to Frits for the Aprilia RSA125 the BMEP was 17 bar
http://www.pit-lane.biz/t117p820-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-lockedWe all learn.
In that Pit-Lane post of 2012 I wrote: "Transmission losses are in the region of 5% per transmission step." Nowadays I think it will be closer to 2,5% which implies that the crankshaft power, torque and BMEP of the RSA were a fraction lower. But at 15,75 it's still better than any other naturally-aspirated petrol-burning engine I've ever seen, including Formula 1.
351822

[Flettner]

Thankyou Frits.

[wobbly]

I have found many times that a 2T racebike on a DynoJet has near on 12.5% losses to the crank power as seen in Engmod if you input realistic data , most importantly Combustion Efficiency , and Exhaust Duct Temp.
So that takes into account tire friction , chain loss ( probably the same as a sprocket power test ) gearbox gear ratio pair and primary pair losses.
This also takes account of the DynoJet fudge factor , built into the software since day one, as they simply didnt believe how bad a Harley really was ,and still is in reality.

[husaberg]

This also takes account of the DynoJet fudge factor , built into the software since day one, as they simply didnt believe how bad a Harley really was ,and still is in reality.
I seem to remember something like a either a little more less like 30 HP (or was it 30kw?) for a 883 for the mid 90's? potato potato.....
i have never ridden a std one but i once rode a highly tuned 1200 one that had had an additional 12g spent on it that was nearly as fast (in the straight line anyway) as a std 1980's RZ350.


In context in the fifties a decent 650 brit twin could knock out 40HP plus, a decent 500 Goldie single nearly also could do the same.
They also steered a shit load better and weighed 100 pound less.

[SwePatrick]

After using the FOS 2T power correction algorithm in my latest dyno tests , that gives much more realistic power numbers ( for example high mBar ambient air - I had an unbelievable 1040 the other day )
I have discovered that JIS D1001 correction gives almost identical results.
This might be useful on dyno software where the FOS code cant be inputted.
Ive got no idea what the correction data is for this , but it does seem to be much closer than any of the others commonly available.

I tried to search but couldn´t find any info.
What are the advantages with FOS correction?

Rgds

[andreas]

Patrick, it was discussed a few pages back.

[wobbly]

The usual SAE and J corrections were specifically designed for 4T use.
The 2T responds very differently to air pressure and ambient temp - more especially toward the extremes.
They are nowhere near accurate at 10*C or 35*C , nor at 900 mBar or 1040 mBar pressure and seem to give abnormally low Hp at the reference conditions as well.

This makes a joke of me trying to gain 1/2 Hp when the correction for the day is already 2Hp wrong.
Means I have to do a " stock " or baseline test every day to get anything like an accurate comparison - and this is often just not possible as the baseline run I did yesterday with a particular
cylinder configuration, I cant replicate as Ive just spent a day grinding the ports.

[diesel pig]

I have recently became very interested in Frits's 24/7 Inlet system and I am now kicking myself for not saving all Frits and others posts on the subject. The problem is my Google Fu is so weak I am doing no good finding the posts now. If only a great Google'er like Master Husaberg could do it, who could probably do it in no time. Oh well ever mind.

[F5 Dave]

I seem to remember something like a either a little more less like 30 HP (or was it 30kw?) for a 883 for the mid 90's? potato potato.....
i have never ridden a std one but i once rode a highly tuned 1200 one that had had an additional 12g spent on it that was nearly as fast (in the straight line anyway) as a std 1980's RZ350.


In context in the fifties a decent 650 brit twin could knock out 40HP plus, a decent 500 Goldie single nearly also could do the same.
They also steered a shit load better and weighed 100 pound less.

The 1340 evos pushed out a fairly impressive 53hp I seem to recall, which at the time was the same as my RZ350 on Sayles dynojet with a head skim and roadbike port clean. There may have been a weight disadvantage but we never measured which bike was heavier ;).

That market dried up for him as he unhelpfully increased power a little by removing screaming budgie go faster parts and jetting. Then Wellington motorcycles bought a new type of dyno that produced the correct type of Hardley horsepower numbers well in excess of his DJ.

[SwePatrick]

The usual SAE and J corrections were specifically designed for 4T use.
The 2T responds very differently to air pressure and ambient temp - more especially toward the extremes.
They are nowhere near accurate at 10*C or 35*C , nor at 900 mBar or 1040 mBar pressure and seem to give abnormally low Hp at the reference conditions as well.

This makes a joke of me trying to gain 1/2 Hp when the correction for the day is already 2Hp wrong.
Means I have to do a " stock " or baseline test every day to get anything like an accurate comparison - and this is often just not possible as the baseline run I did yesterday with a particular
cylinder configuration, I cant replicate as Ive just spent a day grinding the ports.

Thanks for the answer(i DID read the earlier discussion)
But i was asking kind of sloppy, i wanted to know more why the FOS correction corrects more than any other correction.

Rgds.

[Frits Overmars]

i wanted to know more why the FOS correction corrects more than any other correction.

351453Did you read the two SAE papers I mentioned in the PDF, Patrick?

[husaberg]

I have recently became very interested in Frits's 24/7 Inlet system and I am now kicking myself for not saving all Frits and others posts on the subject. The problem is my Google Fu is so weak I am doing no good finding the posts now. If only a great Google'er like Master Husaberg could do it, who could probably do it in no time. Oh well ever mind.

....................



That's Herr Helmholtz messing up things for you, Wob. https://en.wikipedia.org/wiki/Helmholtz_resonance
The cycle from a positive crankcase pressure differential accelerating the transfer flow to a negative case differential slowing that flow velocity back to zero again takes a fixed amount of time. At low revs this time is less than the total transfer opening time, so the cycle continues, performing more than half a sine wave during the open transfer period.
It's the same phenomenon you can observe with piston-controlled inlet systems, where at low revs blowback can occur although the piston is still on its way up towards TDC, so the crankcase pump is still trying to inhale.

In theory the reed valve inlet system ought to prevent the crankcase pressure from dropping below atmospheric. In practice the reed valve needs this pressure drop before it will even think about going to work.
Neils gibs-controlled rotary inlet system offers the best of both worlds. Although.... you may remember Roland Holzners 24/7 experiment at Modena a couple of years ago. Roland realized it without any electronics because the CIK would have vetoed that. His system worked, but with the karting world being the karting world, the CIK vetoed it anyway, like it had done with Rolands synthetic inlet inserts some time before. If the CIK doesn't like you, they'll let you know...

Not even a free breakfast, I'm afraid. The problem is not the symmetry of the port timing; it's the duration of the timing. Asymmetry might have worked in the long-gone era of tiny crankcase volumes but these days Helmholtz will hardly be impressed by what the piston happens to be doing.


The video tells it all: blowback from the 24/7 carburetor whenever its throttle is opened, wich is only to be expected considering the Helmholtz resonance frequency there: conventional crankcase volume, big carb diameter, short inlet tract, low revs and infinite inlet timing.
Revving the engine higher before opening the 24/7 carb, like Alex is proposing, will help, but the best (and simplest) solution is to increase the inlet tract length.


I love watching "Two Stroke Stuffing" on YouTube and seeing how Alex Degnes is enjoying his hobby and at the same time is doing a wonderful job at promoting the two-stroke engine. Of course I also enjoy the way he makes good use of information, like the transfer layout in his present cylinder which mirrors my scavenging concept, his plan to incorporate my 24/7 inlet timing, and now his new cylinder with symmetrical scavenging.The latter will give him a lot more blowdown angle.area than his unbridged exhaust port experiment, and a lot more transfer angle.area to go with the enhanced blowdown.
I can't wait to see his next videos. I don't mind admitting that from time to time it's not only a trip down memory lane for me, but also a shameless ego trip :p.
348909348908348906 348907 348910


I fully agree, Adreas; I'm just writing it down step by step.
Duct volume V = cross flow area A * duct length L
The mass m in our duct is proportional to the duct volume V
m ≈ V
m = A * L
The pressure differential p over this duct exerts a force F= p * A upon mass m
acceleration a is force / mass ;
a = F / m
a = (p * A) / (A * L)
a = p / L
In English: the acceleration of a mass in a duct is proportional to (pressure / length) . If you double the length, the rate of acceleration will be halved, and vice versa.


While we are at it, let us take a look at the amount of mass that is moved through the duct in a given amount of time.
First, let's make some assumptions in order to keep things simple (my hobbyhorse, as y'all may have noticed).
1: The pressure differential over our duct is constant (in reality it would drop because of mass moving from the high-pressure side to the low-pressure side of the duct).
2: The duct ends in a port which is fully opened during t seconds, after which it is suddenly closed.
The length of the gas column that passes through the port, is ½ * (acceleration a) * (time t)²
Now if we compare a duct with length L to a duct with a length 2L the acceleration in duct L will be twice as high as the acceleration in duct 2L, as we have seen above.
This means that with the same pressure differential and the same amount of open port time, the long duct will fill the cylinder only half as well as the short duct. It's a great reason for using a short inlet duct which allows us to use a short opening time.



The 24/7-inlet idea arose in 1974 when the rotary inlet disk of my racer stuck open and it just kept running, as long as I kept the engine in the power band. It meant that I rould ride back to the pits instead of pushing through the grass alongside the track side (which I had already done often enough...).
This experience proved what I already knew in theory: that the pumping effect of the crankcase only serves to start the engine; as soon as it runs in the power band, the exhaust pipe takes care of all the gas movement.
So how do you build a rotary disk that stops in the open position when the engine revs reach the power band?
I had no idea...
But then why would you need a rotary disk anyway? Because it flows better than a reed valve? That doesn't matter when you only need it to start the engine. And a reed valve is much simpler to open...

Below you see an old prototype with a typical design error: it is too complicated. You do not need two gear-coupled reeds; one reed that swings out of the way would be enough. And it can be operated by the same servomotor that operates the exhaust power valve Very Happy .

Maybe not, indeed. My bike was rotary but that didn't stop it from running the wrong way around. Carburation was way off, of course, with a disk that opened 65° before TDC and closed 40° before BDC, but it ran anyway.
Heck, it even ran when the disk hexagon was smashed and the disk stuck open permanently. It was the birth of the 24/7 idea.

There are practical limits at both sides of the inlet timing. You can open the inlet as soon as the pressure in the crankcase has dropped to the pressure level upstream of the inlet disc.
Open it any earlier and you will lose crankcase pressure to the outside world; open it any later and the crankcase pressure will drop more than it needs to, slowing down the transfer flow.
The Helmholtz resonance of the blowdown+scavenging cycle determines how many milliseconds after exhaust opening the pressures upstream and downstream of the inlet disc are equal.
This fixed amount of time means that at low revs you could open the inlet even before BDC. But this is impractical for two reasons (unless your name is Neil Hintz).
A: The inlet needs to open later as the revs increase.
B: Opening the inlet exactly when the pressures upstream and downstream of the inlet disc are equal means that there wil be a zero-pressure opening signal sent to the carburetor, and carburetors don't respond well to something they don't notice.

Summary: opening the inlet too early or too late will both cost power, but opening it too early will cause more problems than opening it too late.

When should we close the inlet? When the inlet flow is slowed down to zero by the ever-rising crankcase pressure. Close it any earlier and you will miss out on the last bit of crankcase filling; close it too late and you will lose mixture flowing back from the crankcase towards the outside world, passing the carburetor on its way out and taking some more fuel with it. This same amount of now overly-rich mixture will be sucked in again at the next inlet cycle, passing through the carburetor for the third time, taking some fuel with it for the third time and trying to drown the engine.

Summary: don't close the inlet too late. For a well-developed racing engine 85° after TDC will be about the limit. If you are really power-hungry, you can try a couple of degrees more, but it may harm your lap times.

If you do find more power past 85°, you may instead consider returning to the 85° closure timing and fitting a bigger carburetor.
By the way, 85° after TDC is also considered the maximum foolproof timing for a piston-ported inlet system.

In case you are interested in the Aprilia RSA125 inlet system: cylinder capacity=124,8 cc; crankcase volume @ TDC=675 cc; inlet timing= 142,5°/88°; carburetor diameter= 42 mm.

So this is it? Not quite yet, because closing the inlet too early can also give strange effects, as I discovered when I put an experimental distance piece between the carburetor and the inlet disc.
This increased the inertia of the inlet column, so this column came up to speed slower, and was subsequently cut off by the closing inlet disc while it was still flowing towards the crankcase at a respectable speed. The sudden closure caused a high collision pressure upstream of the inlet disc and the mixture column bounced back like you wouldn't believe. It filled the entire dyno room with a mixture mist within seconds, and the tiniest spark might have blown the roof off. Ever since this experience I distinguish between blow-back, which is a nuisance, and bounce-back, which is outright dangerous.


The simplest solution for totally asymmetric and variable inlet timing is the common reed valve; it doesn't need any governing. It won't flow as well as a rotary valve,
but below the power band that doesn't matter. And once we're in the power band we can hold it open 24/7 as you say. A simple servo motor can do that; we can even use the exhaust power valve servo if there is one.
No need for any electromagnets. I doubt if those could be fast enough for cycle-to-cycle operation anyway. It's not like lifting an injector needle 0,1 mm off its seat;
a reed valve should move about a hundred times further, but at the same frequency as that injector needle....


I doubt that Muhr. I don't know when Tassinari started producing its Vforce reeds, but I do know that my first 24/7 prototype dates from the previous millennium :first:.
336062

Joking apart, I think it's possible that a conventional reed starts behaving like a 24/7 inlet when the engine frequency rises above the reed's natural frequency,
but it will still offer a lot of flow resistance. Better swing the reeds out of the way altogether.


Running it: yes. Starting it: no.
That is why my 24/7 inlet system has a hinged reed that can be shut for starting the engine in the conventional reed-mode, and that can be swung out of the way, once the engine is running in the power band and the exhaust pipe suction is taking care of things.


The advantages of a 24/7 inlet are an unrestricted mixture flow with better symmetry than a sidemounted rotary valve and minus the friction of that rotary valve.
A 24/7 inlet is no use at all below the power band, as you have already found out. But in the power band it can give good cylinder filling, and power in the overrev tends to be better than in the case of a rotary valve, unless you do a Flettner with variable rotary valve timing on the fly, but controlling that will definitely be more complicated than controlling a 24/7 valve. By the way, starting a 24/7 engine without any starting valve at all may be a pain; you've found that out as well.
That is why I designed it with a simple reed that swings out of the way, once the engines runs in the power band.
Experimenting with different inlet tract lengths is the way to go. In theory you could also experiment with different carb diameters and different crankcase volumes,
but changing a length piece is a lot simpler.


Carb-wise there are no special requirements. But I've got some other pointers for you.
Try to accommodate the 24/7-housing in the reed cavity of the crankcase, so you can switch between both systems. Then, build and run the engine with a normal reed, so you can be sure that there are no hidden problems.
The necessary inlet tract length depends on crankcase volume, carb diameter and rpm of maximum power. This rpm is established by the cylinder's angle-areas,
so it is more or less fixed, and also there's only so much you can do to enlarge the crankcase volume, but you are free in your choice of carb diameter.
As a guideline, try SQRT(cylinder capacity x rpm of max.power / F). This factor F should be about 1200 (for conventional inlet systems F should be about 900).
This set-up will leave the inlet tract length as the value to play with. And it may need to be quite long, maybe 350 mm from carb bellmouth to 24/7-flap,
and even longer if you use a big carb, so it will be wise to allow for quickly-exchangeable distance pieces.

Alex, that bolted-together accessory that you used to explain the effects of twisting, is a great idea to make clear what is going on.

PS: If you over-pinched your crankshaft, you can of course open it up again with a chisel and a hammmer, but I prefer to use a 'reversed vice'. That's just an M8 or M10 bolt, shortened so much that it will fit between the crank webs, and a nut. Unscrewing the nut will give you much more control than hitting the chisel with a hammer.

PS2: I suppose it's past sunday over there, but anyway: Happy Birthday ESE!


I am not at liberty to say any more about it than I already did here, Haufen. You may want to search for 'Modena' and 'Roland Holzner'.OK, this is a question I can answer because it was obvious for all the world to see that the Modena 24/7 uses the normal homologated 30mm Dellorto carb.
My fears that injection would be necessary were not confirmed. The Modena runs fine with a carb, notwithstanding the fact that they also have a working injection system on the shelf.

The 24/7 system depends on the pipe even more than a conventional inlet system does, but the pipe itself does not need to be altered.
Crankcase volume, inlet length and carb diameter all play a role; none of those values are critical, but their combination should yield a suitable Helmholtz frequency.
The most practical way to go about this would be to start with a fairly big crankcase volume and a fairly small carburettor, vary the inlet length and see what happens.


The international kart governing body FIA-CIK considers electrickery a thing of the devil; they do not even allow variable ignition or electric power valves and power jets. And I'm convinced that they will find a way to block the 24/7 Modena even though the valves are purely mechanically operated.
Modena and the CIK don't exactly see eye to eye; after Modena introduced its synthetic flow-guiding inlet insert, the other kart engine manufacturers conspired and the CIK announced that the insert would not be accepted again at the next homologation round, although it's just a piece of plastic that every manufacturer could make at next to no cost. In fact it was initially developed by Modena so the complex milling of the transition from the reed cavity to the transfers could be skipped. My suggestion to use a plastic with low thermal conductivity also contributed a bit to engine power.


Didn't I already tell? I thought I did. The direct inlet version evolved into the 24/7 version which produces 10% more power than the regular Modena engine (with the same obligatory 30 mm carb, pipe, compression volume etc.)
BTW Ken, nice analysis.


Great minds think alike, Ken. The picture below shows the onset of an experimental Modena engine, created by my friend, Modena technical director Roland Holzner.
312417

If you take this idea further and concentrate on eliminating its drawbacks, as Roland did, you'll get this:

312418 312419

That's right: 24/7 :D
http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130867376#post1130867376


Thank god, finally a remark that I can comment on without violating the Ryger non-disclosure agreement.
Yes, you could employ an additional reed. But why would you? The 24/7 valve itself is a reed; how much simpler do you want things to be?


Roland has one huge handicap: the rulebook. The carburettor diameter is restricted to 30 mm. That of course influences all other dimensions in his inlet system.
A second handicap is that none of these kart engine manufacturers has unlimited funds. Roland had to avoid upsetting the beancounters so he worked with what he had.
Besides, even if money would not be an obstacle, Kart engine manufacturers cannot change an engine at will because of homologation issues.
Rolands primary goal is to get his fuel injection approved, which won't be easy because he already rubbed some stone-age officials up the wrong way with the synthetic inlet inserts in the present Modena engines. These were homologated all right, but subsequently the officials let Modena know that these inserts won't be accepted in future engines. Why? All I can think of is envy.


In the long run: yes, I think so. But there are many people here working on rotary inlets and for them it is simpler to carry on than to switch to 24/7.
On the other hand, if you are already working on a reed valve engine, converting it to 24/7 is much simpler than converting a rotary valve engine.
And finally I am in a position that I don't need to push everyone into 24/7; it's already on the move: http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130808805#post1130808805

That was my initial fear too, Smitty. That was one of the reasons I was so keen on dropping the carburettor and switching to fuel injection. But the Modena tests have shown that a single carburettor can handle the switch from a closed to an open 24/7 inlet without any problems. And Modena have also got a conventional reedvalve kart engine running quite nicely on injection so they know what they should be looking for.

No maybe's about it: more complex and more difficult to tune. Are you sure that deep in your heart you're not a double-overhead camshaft man, Smitty?:devil2:

Clearance should be about 0,4 mm. And the disk should be able to float until it rests against either side of the disk chamber. That makes setting it up a whole lot easier.
Remember the 12-speed twin-disk Kreidlers? They had both disks pressed onto the crankshaft. Getting them well-sealing yet friction-free was a nightmare.


The main advantage of EFI on a kart is that the motorcycle carbs everyone is using were never designed to handle acceleration in four directions. It's the one factor that gives more trouble on kart engines than all other factors put together.
Riley Will of BRC is already achieving good results with EFI and so is Roland Holzner of Modena engines in Italy. But injection has yet to be homologated on 125 cc karts, which could be a special problem for Modena. Their heat-insulating inlet insert was already more advanced than the ultraconservative FIA-CIK officials would have liked to see and you can imagine how they feel about Modena's experimental 24/7 engine which does not seem to care about their obligatory 30 mm inlet restriction.


As long as that tract is not as short as it could be, I will call it long.
http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=306810&stc=1&thumb=1&d=1419079180and don't tell you won't be able to get to that top disk cover bolt :msn-wink:.

Where else? Imagine that you are in a test cabin and the total air entrance to the cabin is a 24 mm orifice. You can be sure that the air flow through that orifice will be 24/7, not just 220° out of every 360 crankshaft-degrees. That's 60% better...

It can be, but this will inevitably mean that there will be circumstances where the resonance works against the engine rather than with it.
With EFI you don't need to worry about fuel dropping out of the mixture due to too low a flow velocity, so make that plenum a big as you can; think Samsonite.


At the time Jan was thinking about the RSA inlet disk position and he wanted to find out whether the direction of crankshaft rotation had much influence on the inlet flow. So he put a standard kart engine on the test bench, measured the power, started it in reverse and measured the power again. 'Reverse' , meaning the crank rotating backward, gave one extra horse.
I discussed this with Roland Holzner of Modena Engines the other day and he told me that they'd already performed the same test at Rotax. Roland said that the negative effect wasn't so much due the counter-flow induced by the crank webs, but mainly due to the fact that the fat end of the con rod was directly in front of the reed case at the moment of initial inlet flow.


Here's some more Helmholtz-encouragement:

Regarding induction systems: build a short induction tract and visit a test bench.
You can forget about calculations. The formulas you find in various books are all based on the Helmholtz resonator. It made me write a simple story, called:
Helmholtz blues
"A Helmholtz resonator consists of a volume connected to a duct". That is what Wikipedia tries to tell you.
But that is a Helmholtz resonator in its simplest form; one that you won't find anywhere in an engine.
What you do find in an engine is an intake tract with a variable cross-sectional area. This tract is from time to time connected to a variable volume (the crankcase) through a very variable window (the intake port / reed valve / rotary inlet).
The crankcase is connected to a number of transfer ducts with variable cross-sectional areas, which are from time to time connected to a very variable volume (the cylinder) through a number of very variable windows (the transfer ports).
The cylinder is from time to time, through a very variable window (the exhaust port), connected to an exhaust pipe with a very variable cross-sectional area who at the same time doubles as a volume. This pipe volume is constantly connected to a big volume (the outside world) through a tailpipe with a constant cross-sectional area and constant entry and exit windows (thank God, finally someting that's not variable).
We call this a compound Helmholtz resonator .
The various papers also tell us how to calculate the resonator's frequency:
" frequency = speed of sound / (2*pi)* Sqr ( cross-sectional area of the neck / ( volume of the resonator * effective neck length ) ) ".
O yes, the speed of sound... It is dependent on temperature, which is not really constant in the intake tract and the crankcase, rather variable in the transfer ducts and very variable in the cylinder and the exhaust pipe.
Now the above frequency formula is not exact; it is an approximation that is usable as long as the volume of 'the' tract is very small compared to the resonator's volume.
So when engines are concerned, that formula goes very far out the window.
Who said gas dynamics is simple dull?
PS:
It's a similar story with acoustics. That is a sub-branch of gas dynamics, simplified with a lot of assumptions that are acceptable as long as the sound pressure does not exceed a certain limit. The wave pressures in a two-stoke exhaust exceed that limit by a factor of thousand. Bye bye, acoustics...


For me: FOS symmetrical schavenging, 24/7 inlet system, continuously variable transmission; not even remotely related to a Rotax based single.


Helmholtz frequency, my dear Watson. The smaller crank will give the pipe more crankcase volume to breathe from. This larger volume will also lower the resonance frequency of the inlet system, hence the drop at high rpm. It can be compensated with a shorter inlet tract, a bigger carb diameter and a later inlet closure. To put it real simple: if you have more volume, you need more time to fill it. But more time, i.e. later closure, has adverse effects at low revs. So my preference is a shorter tract (unless you go the 24/7-way and employ a reed for the low revs, and swing it out of the way at high revs).


I would stay away from air-cooled racing engines at all costs.Then again, I would find a way around the carb diameter limitation; take a look at www.pit-lane.biz (http://www.pit-lane.biz) where I explained the backgrounds of my 24/7 inlet system.

[Vortex]

Hi guys,
On my dyno software i have a few options concerning the correction, starting with "off" means no correction from ISO and DIN to 95/1/CE.
By default the 95/1/CE is in use together with a connected meteostation installed in the dyno room and unfortunately without any possibility entering values manually.
Now i'm trying to convince the manufacturer in Italy that at least i would like to take the temp. in the airbox and not in the room as the reference.
What do you think about, 1. the used correction and 2. the place where the reference temperature is taken?

Thank you in advance
Vortex

[diesel pig]

It's like the Great Master is reading my mind. If only I had a mind worth husaberg reading.

[ken seeber]

Hewzer, thanks for putting up the collation of 24/7 by Frits.
Absolutely legendary stuff.

[Frits Overmars]

Hewzer, thanks for putting up the collation of 24/7 by Frits.
Absolutely legendary stuff.Boy, did I write all that stuff? I suppose I've earned a piece of apple pie with my coffee :p

[wobbly]

Strudel , where you are now Frits

[husaberg]

I have recently became very interested in Frits's 24/7 Inlet system and I am now kicking myself for not saving all Frits and others posts on the subject.

If someone asked Neil H nicely i am sure he could make DP (Neil B) a Sliding Weed valve like this one

<a href="/gif/supercharged-50cc-two-stroke-breakthrough-F2-7oL" title="Supercharged 50cc Two Stroke BREAKTHROUGH!"><img src="https://i.makeagif.com/media/10-28-2022/F2-7oL.gif" alt="Supercharged 50cc Two Stroke BREAKTHROUGH!"></a><div style="font-size:11px;">make <a href="/" title="make a gif">sports GIFs</a> like this at MakeaGif</div>


https://youtu.be/3StKrITOaw4?t=39

[ken seeber]

Just wonder if old mate Alex wouldn't be a lot better off with a turbocharger. No direct mechanical parasitic losses and also raises the overall in-cylinder pressure at the time of EPC due to the back pressure of the turbo.
Dunno if one could get one that is small enough, but he could make one, adding a variety of spice to his adventures.

[husaberg]

Just wonder if old mate Alex wouldn't be a lot better off with a turbocharger. No direct mechanical parasitic losses and also raises the overall in-cylinder pressure at the time of EPC due to the back pressure of the turbo.
Dunno if one could get one that is small enough, but he could make one, adding a variety of spice to his adventures.

i think it was basically std but not 100% sure though.
351833

https://youtu.be/Oxj_OAb5bqk

it could have freed up a bit of spare time for Fits and Jan just those pesky rules prevented bolting on a few snails.
Oh look they did a 50cc as well
351834


https://www.youtube.com/watch?v=gv377_f3cvU

[diesel pig]

If someone asked Neil H nicely i am sure he could make DP (Neil B) a Sliding Weed valve like this one

<a href="/gif/supercharged-50cc-two-stroke-breakthrough-F2-7oL" title="Supercharged 50cc Two Stroke BREAKTHROUGH!"><img src="https://i.makeagif.com/media/10-28-2022/F2-7oL.gif" alt="Supercharged 50cc Two Stroke BREAKTHROUGH!"></a><div style="font-size:11px;">make <a href="/" title="make a gif">sports GIFs</a> like this at MakeaGif</div>


https://youtu.be/3StKrITOaw4?t=39

I must admit I was reminded about Frits 24/7 inlet system by 2stroke stuffing video's but I could not remember it's details. Thanks for the help, O Great husaberg
I am interested in the Kart company that experimented with this system and found 10% increase over it's full time reed valve inlet system. I wonder if this was only
at the very top of the rev range or did the increase start earlier? either way interesting stuff! and I must say the Norwegian has almost Kiwi level of "lets try
something weird and see what happens" keenest, which I think made his video's so interesting.

[andreas]

He says the rev limiter is set at 13500, and that this is at least 1000 too low.

https://www.youtube.com/watch?v=zybsu4Mwato

[husaberg]

I must admit I was reminded about Frits 24/7 inlet system by 2stroke stuffing video's but I could not remember it's details. Thanks for the help, husaberg
I am interested in the Kart company that experimented with this system and found 10% increase over it's full time reed valve inlet system. I wonder if this was only
at the very top of the rev range or did the increase start earlier? either way interesting stuff! and I must say the Norwegian has almost Kiwi level of "lets try
something weird and see what happens" keenest, which I think made his video's so interesting.

http://www.pit-lane.biz/t117p435-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked

Mr Overmars will be able to provide details for what where i would suggest or at least point to in the right direction to Rolands and others tests

[SwePatrick]

Just wonder if old mate Alex wouldn't be a lot better off with a turbocharger. No direct mechanical parasitic losses and also raises the overall in-cylinder pressure at the time of EPC due to the back pressure of the turbo.
Dunno if one could get one that is small enough, but he could make one, adding a variety of spice to his adventures.

Added power through the same stingerdiam also raises backpressure.

[ken seeber]

Added power through the same stingerdiam also raises backpressure.

A crude way to raise the back pressure and still have the parasitics....

[Frits Overmars]

http://www.pit-lane.biz/t117p435-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-lockedMr Overmars will be able to provide details for what where i would suggest or at least point to in the right direction to Rolands and others testsI am not at liberty to divulge more than I already have. Roland has been doing most of the work so it's only fair that he will decide how much he is going to reveal, not me.

[diesel pig]

I am not at liberty to divulge more than I already have. Roland has been doing most of the work so it's only fair that he will decide how much he is going to reveal, not me.

Fair enough, about Roland's work . I only asked because along time ago I read (probably on this very thread!) that one could increase the bottom end power on a Two Stroke Reed valve by using "Softer Reeds*" but one would have to accept that this would lead to power problems with the Reeds at the top end of the revs range. But since the 24/7 system does not use reeds for Intake at the top end of the revs only really at the bottom end of the revs. I was just wondering whether this could be taken advantage of to 'boost' the Bottom end power of the system?
A interesting idea Husaberg but I think like a lot of people 'Life' is getting in the way of the interesting things at the minute. It would be a interesting to experiment with the 24/7 system when I get the opportunity.

*I don't know if that means thinner or less harder reed material. Probably a combination of the two.

[wobbly]

" I don't know if that means thinner or less harder reed material. Probably a combination of the two ".
Thinner is usually softer , but weave orientation is just as important , as you can construct a thinner petal that is stiffer due to the weave direction.
And of course the backups are a whole can of worms in their own right - creating multiple stiffness regimes dependent upon tip lift.

I have been midnight dreaming as well , thinking a soft petal could be arranged in such a way that when a preset lift is exceeded , the reed flips some yet to be determined clamp mechanism, over center.
Then the petal sits at full lift, a one shot device - but once past the finish line , who cares what happens next.

[F5 Dave]

Bubba Shobert, and well there's a heap more but yeah, always best to pay attention after the finish line.

[husaberg]

Bubba Shobert, and well there's a heap more but yeah, always best to pay attention after the finish line.
i was trying to remember whose bike hit Magee's bike, it still makes me feel queasy.


I am not at liberty to divulge more than I already have. Roland has been doing most of the work so it's only fair that he will decide how much he is going to reveal, not me.
Sorry i thought he had posted it on Pitlane i have lost my password and couldn't be assed looking.

[Frits Overmars]

....I read (probably on this very thread!) that one could increase the bottom end power on a Two Stroke Reed valve by using "Softer Reeds*" but one would have to accept that this would lead to power problems with the Reeds at the top end of the revs range. But since the 24/7 system does not use reeds for Intake at the top end of the revs only really at the bottom end of the revs. I was just wondering whether this could be taken advantage of to 'boost' the Bottom end power of the system?You have a point, but it depends on how you define bottom end power. For me it's the initial part of the power band, and if you are anywhere in the power band, the 24/7 reed should already be swung out of the way, so it won't matter how hard or soft it is.
Below the power band a soft reed would have benefits, as you say, but it will never be enough to justify running below the power band.

[andreas]

Trial&error attempt YZ 85.
Production continues slowly, and revised with thicker gauge sheet for better durability and aestetics.

[diesel pig]

You have a point, but it depends on how you define bottom end power. For me it's the initial part of the power band, and if you are anywhere in the power band, the 24/7 reed should already be swung out of the way, so it won't matter how hard or soft it is.
Below the power band a soft reed would have benefits, as you say, but it will never be enough to justify running below the power band.

I must admit I was really just thinking out loud. I was wondering with that question about the reeds, if the 24/7 system had a really strong bottom end power curve that might help the 24/7 system as it came into the start of the main power band curve. I think just like the ones who came up with the ideas for things like performance exhaust pipes and multiple transfer ports, they knew these things, it would increase performance but didn't know at the start of their ideas by how much power it would add or what the power curves would look like until they built them and tested them. The more I find out about the 24/7 system the more interested I am in it. Thank you for telling us about it.

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/3NlkF6YBlhg" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

<yt-formatted-string force-default-style="" class="style-scope ytd-watch-metadata">Supercharged 50cc Two Stroke Turbine Flutter & Flamethrower!</yt-formatted-string>

[dutchpower]

Trial&error attempt 1. YZ 85.

What year yz 85 Andreas

[andreas]

It's a 2023.

[andreas]

I was randomly strolling around the pages, when I set foot at p1500 onwards, alot of interesting stuff going on here, the 2-1 pipes and Wobblys exhausteside piston cutaway seadoo. Can't even imagine how that idea came to being an how erratic the induction would have been. Maybe it will work also on a regular engine, but using the 2nd reflections depression wave when it reaches the face of the piston at TDC?
Also I see at various places Frits mentioning the Helmholtz effect on the tuned pipe, but haven't seen how it actually work. and to what extent. Maybe you can do a nice lecture on this subject?

[Frits Overmars]

.... I see at various places Frits mentioning the Helmholtz effect on the tuned pipe, but haven't seen how it actually work. and to what extent. Maybe you can do a nice lecture on this subject?I did, some time ago, on another forum. Unfortunately I can't find the English version, but maybe the original German version will be of some use to you.
To be taken with Aspirin :msn-wink:.
351848

[andreas]

Thanks Frits. I'll do my best with the translation.

[Frank S.]

Hi,
here is a write up about the intake helmholtz resonance.
Frits called it the Helmholtz-blues

http://www.pit-lane.biz/t117p740-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked

[andreas]

Frank, yes I've read the Helmholtz Blues.

[lodgernz]

I did, some time ago, on another forum. Unfortunately I can't find the English version, but maybe the original German version will be of some use to you.
To be taken with Aspirin :msn-wink:.
351848

hier ist die englische version:
351854

[andreas]

hier ist die englische version:
351854

Vielen Dank

[wobbly]

The piston cutaway idea came from staring at Dynamation pressure wave screens for hours with a 2 into 1 being modelled.
It only worked with in excess of 200* Ex duration and at the time I thought how impossible it would have been to tune if not using a pumper carb setup.
They function almost like fuel injection in that a throttle body size that is way too big to be tuned correctly if a carb was used , due to the low velocity at low rpm/WOT , giving low depression values ,make jetting impossible.
The pumper can be made to change the fuel curve dramatically at any rpm/throttle position using the pop off pressure , lever height , with dual fixed and screw adjustable pilot and main systems.
They are unique also in that the idle/pilot progression holes arrayed in front of the butterfly as it opens , also actively function as main air correctors at WOT - thus enabling all manner of tuning anomalies to be
overcome.

[dutchpower]

Trial&error attempt 1. YZ 85.

Andreas test it like this save you lot of work you can make changes quicker

[andreas]

Very interesting Wobbly. Yes pumper carbs are mostly out of my scope.

[andreas]

Andreas test it like this save you lot of work you can make changes quicker

I don't really follow how you mean?

[F5 Dave]

He means i believe as a straightish pipe hanging out and then make snake like when you are happy.

[dutchpower]

He means i believe as a straightish pipe hanging out and then make snake like when you are happy.
Yes :niceone:

[andreas]

Ok, I see. It isn't going on a dyno, and elongate/shorten belly/header is not so hard.

[dutchpower]

Ok, I see. It isn't going on a dyno, and elongate/shorten belly/header is not so hard.

Oke Andreas

[wobbly]

Once again Frits is on the money.
My empirically derived idea of exhaust duct exit reduction to 75% of the effective Exhaust Port area works very well as a guide to the size to be looking for.
Frits has always maintained the exit area should be tied to the Blowdown capability.
Here we have a case of the Blowdown , that is optimized to achieve a relatively modest 13 Bar bmep , achieves Mach 0.8 at the pinch point with a 71% area reduction.
Smaller looses power as does a larger exit diameter.
It seems the only way to optimize this factor is by tracking the Mach number to achieve 0.8.

[Tim Ey]

Once again Frits is on the money.
My empirically derived idea of exhaust duct exit reduction to 75% of the effective Exhaust Port area works very well as a guide to the size to be looking for.
Frits has always maintained the exit area should be tied to the Blowdown capability.
Here we have a case of the Blowdown , that is optimized to achieve a relatively modest 13 Bar bmep , achieves Mach 0.8 at the pinch point with a 71% area reduction.
Smaller looses power as does a larger exit diameter.
It seems the only way to optimize this factor is by tracking the Mach number to achieve 0.8.

Hi Wob,
bore is apparently 59mm, may you tell us the stroke?

Regards
Tim

[porttiming124]

Hi Wob,
bore is apparently 59mm, may you tell us the stroke?

Regards
Tim

Tim here is a small calculation to find the bore .

51.8/71.9*100 = 72 mm

[wobbly]

Yep , she's a big bore dragster.
72 B X 63 S - Rod 130 = 256,5cc
So the power is limited by the huge oversquare ratio compromising STA but also it can't be rev'd hard due to the heavy piston even though the stroke should easily go to 11000.

[Tim Ey]

Tim here is a small calculation to find the bore .

51.8/71.9*100 = 72 mm
Ouch. Wrong window. I did the very same calculation with the Effective Port Diameter :laugh:


Yep , she's a big bore dragster.
72 B X 63 S - Rod 130 = 256,5cc
So the power is limited by the huge oversquare ratio compromising STA but also it can't be rev'd hard due to the heavy piston even though the stroke should easily go to 11000.

I would agree: the exhaust window area is right on the money.
Regarding the 75% rule in general, I tend to disagree:
The Flange will be allright when:
Flange-Area = .75 x BigEnoughExhaustWindow-Area

but the Flange will be too small when:
Flange-Area = .75 x NotEnoughExhaustWindow-Area

In that case, using a Flange-Area that is too big (>75%) can compensate for an exhaust port that does not supply enough area for the desired power.

[wobbly]

Now I disagree , as the proven 75% exit area works perfectly on a TM or an Aprilia , if you then have an Exhaust port that makes sub optimal power by not having sufficient Blowdown area -
then as the above example shows , a smaller exit % of 71% in this case works way better.
That is , as Frits has said , the exit area is a function of the Blowdown capability , and that is what sets the bmep achievable - low bmep = low exit flow = smaller area needed to hit 0.8 Mach.

[andreas]

Kawasaki Mach4 for sure.

[dutchpower]

Kawasaki Mach4 for sure.

Did you test the pipe Andrea

[andreas]

Did you test the pipe Andrea

Not tested, it wasn't finished before I opted for thicker walls.

[Condyn]

Apologies in advance for questioning a very old, tried and trued idea.

With the concept of weight savings set aside, what is the purpose of the piston cutouts under the wrist pin? I understand they keep the transfer entrys un shrouded. I have read in this forum that the amount of mixture to enter the scavenging column does not exceed what is stored in the transfer passages. It is my interpretation that that also means there is no direct communication needed to the crankcase at BDC.

The reason I ask this question is because due to the piston cutaways when the piston is at TDC, there is a direct link from the intake port to the transfer windows in the cylinder. (on all engines I work with)
Would this not cause a turbulent reverse flow backwards down the transfer duct before the descending piston opens the transfer windows?

[andreas]

If the amount of gas in the tranfer ducts is all that enters the cylinder probably depends on how much volum they hold. Regardless, they need to be backed up by the crankcase, otherwise the vacuum in the ducts would be too great, and the delivery would vastly suffer.

[wobbly]

The statement about transfer duct flow into the cylinder was in response to the assumption that at BDC , when the pipe diffuser creates the max cylinder depression , there is communication of
this depression from the cylinder , thru the ducts, into the case - and this pulls mixture thru the reeds.
This cannot happen , as in every race engine I have seen in EngMod , the reeds are only just starting to open after the piston has risen to TPC.
Seeing this, led to the tuning trick of using the intake tuned length to create a + pressure ratio on one side of the petals , at the same time as the case goes negative.
An assumption is just an error waiting to be revealed.

Then looking at purely the mechanical aspects of the duct flow.
Taking the volume as that being from the port faces , down the ducts centerline , around the long turn floor radius in the case , and up to the piston cutaway/bore face ,
there is way more volume in these combined ducts than can ever be " transferred " into the cylinder - even with well over 100% VE.
Simple mechanical facts.
And yes , as the flow exits into the cylinder , there is not a vacuum " left behind " in the case , any pressure differential is instantly balanced - flow out = flow in , less any inefficiencies due to duct wall parasitics etc

Lastly , re TDC flows in or out of the ducts , yes in a cylinder reed when the inlet port is open , so are the transfer ports via the piston cutaway area.
But in this scenario , sure the transfers ports are exposed , but then so are the duct entries at the other end exposed to the same case volume - thus there is the same pressure delta at either end and no flow in or out can occur.

[andreas]

Question:
Why is a two or three stage converging baffle better, and how to fabricate it, like a parabel?

[wobbly]

The first parabolic converging cones I am aware of were developed for clutch pipes in KT100 Yamaha's.
These were spun cones, but had huge 38mm exit diameters , into an integral can muffler , so it was a bit of a weird design tangent that worked way better than a straight conic section.

The physics behind the idea is that the return wave amplitude is being boosted by the increasing cone angles , as the piston is rising in synch closing the port area down.
Rear cone angles depend upon the belly diameter/volume and the end use , dictating how much overev vs peak power / powerband width is needed for the application.
The bigger the belly , means more of the finite wave energy has ben consumed in the diffuser , thus steeper converging tapers are needed to generate the needed plugging efficiency.

Maybe a good place to start for a new application is to look at the R1 pipe rear cone I did 4 years ago , that has now been reused for the next 3 years in the R2 design , as I simply could not beat it in a sim or on the dyno.
This was iterated down over literally hundreds of sims and confirmed with 3 physical pipe variations on the dyno.

I would draw a straight cone and construct a table with length % and angle increase/decrease % per section.
The most critical section is the last, the steepest.
Its length and internal angle has an almost linear relationship to increasing peak power Vs overev bandwidth.
Too long and or too steep , and peak power increases dramatically - but then after peak it drops almost vertically , probably perfect for a CVT application.

[andreas]

Thanks Wobbly, that is seriously steep, and only 25/61 % header/ end of diffuser.
But how is to end of diffuser 61%, when belly and baffle are 9 and 25 % respectively?
With a 61mm ex-duct, I find to end of diffuser is 65.3%, and header 29.6%.

[wobbly]

Yes the header and diffuser % are abnormally short as this is a maxed out 125 with a straight line ignition that requires a very short pipe.
32% and 65 - 68% would be considered perfectly normal for virtually all configurations , except this particular case.
The belly and thus rear cone length % are dictated entirely by the end use requirement for peak power Vs overev , and vary enormously.
It peaks at 13800 with useable overev to 14800 , thus needing very carefully designed rear cones , and the very steep last diffuser , moved to the left , pumps up the front side from 11000 to 13000.
Another constraint is that going over 50Hp makes tuning very difficult for all but experts , and can end up needing excessive fuel to stop deto - not make Hp.

Useable range is quite narrow , starting at 10,000 WOT , thus a short header is needed to shift the whole powerband up and rightward.
Having a very good overev bandwidth means the possibility of deleting gearchanges on short straights or simply adding rear teeth to gain acceleration from the ratio , and then maintaining terminal speed with rpm capability.
Here is the result of the new engine , showing the suppressed peak used to generate a 1000 wide band now sitting right on 50Hp.

You are right about the % errors , I have no idea how I saved that incorrect layout from EngMod , here is the actual pipe numbers.

[andreas]

Very interesting.

[dutchpower]

Very interesting.
Changes in your pipe Andrea gif more
Can not compair whit std. pipe have no dimention of it

[andreas]

Dutchpower, this is a pipe you've tested?
I'm aiming for a tuned length of 820, starting at 35mm with a shallower header than the original drawing.
I have partial measures of a HGS pipe and probably a standard somewhere, are you asking to see those numbers?

[dutchpower]

Dutchpower, this is a pipe you've tested?
I'm aiming for a tuned length of 820, starting at 35mm with a shallower header than the original drawing.
I have partial measures of a HGS pipe and probably a standard somewhere, are you asking to see those numbers?

Do you have std. pipe drawing

[andreas]

Yes, I can measure it, Will take some time, because it is not at my place.

[lodgernz]

Wobbly, I'm about to build another pipe in my endless quest for more power from my Honda buckets, and I hope you can answer a question that has been puzzling me for a while.

Looking at your ultimate RS125 pipe that you published here a while ago, the length of each diffuser section, as a percentage of the total diffuser length is:
H1: 32%
H2: 52%
H3: 16%

I wondered how you came to these ratios. Was it purely from EngMod, or dyno trial and error, or just some Wobbly magic?

Imagine you were building a pipe for a bucket that had reasonable transfers, peak power at 13000 RPM and needed grunt out of corners but a decent pull to max RPM of, say 14,000, on a bike geared to reach that RPM at braking point on the fastest part of the (kart) track, which is usually less than 200 metres from the previous braking point.

How would you alter those ratios?
Would you still keep the steepest diffuser angle at H2?

[wobbly]

Lodger, I cant remember what the RS125 pipe was to be honest as I havnt worked on one for years now.
Repost it here so it jogs my memory.
But no from what I have learned about pipes needing good power range with no PV I have been making the last diffuser much longer and steeper as this pumps up the front side.
As you can see in the TM design.

The length of the header , combined with the angle of a short first diffuser sets the overev potential , shorter and steeper = more overev past peak.
This short first diffuser really only bypasses the possibility of creating a shock wave situation ( that destroys energy ) by having a way steep section directly off the header.

All of this guidance is iterated out in EngMod , then dyno tested , and of course I would say there is magic involved as well.
And then if you pinch down the cylinder exit to hit 0.8Mach , this mostly increases peak and overev potential , so one use of this is then to make the pipe longer to gain some more low end as well.

[lodgernz]

Here is the hell RS125 pipe design that has basically everything I know embedded in its concept, the 800mm length is for a 200* Ex only with a
proper ignition curve and powerjet switching..
The first 25 mm is an oval transition flange ( 41 by 32 ) in the duct, out to a 41 header.
The stinger nozzle is 23.2 with 25 stinger pipe.
Dual stage header, and steep mid diffuser create the deepest and widest depression around BDC at 13,000, with tons of overev power.
The 120mm Honda and Mota pipes wont even get close, especially with the final diffuser being the steepest,it creates the Ex port depression way too late in the cycle
to help at the natural peak of a 200* Ex around 13,000 and into the all important overev past 14,000.
Several details can be jigged to work better than this design, but thats for you guys with a good code to work with to figure out from looking closely at the pressure ratio traces.

This one Wobbly.

[wobbly]

Post the pipe.

[lodgernz]

Post the pipe.


Sorry Wob, this one, and thanks for your great reply.

351928

[wobbly]

What was the pipe called , was the EngMod project name up at the top.
If I get a dull moment I will update it for you.

[lodgernz]

What was the pipe called , was the EngMod project name up at the top.
If I get a dull moment I will update it for you.

Can't see a name anywhere. Here are the EngMod details

351930

[dutchpower]

Dutchpower, this is a pipe you've tested?
I'm aiming for a tuned length of 820, starting at 35mm with a shallower header than the original drawing.
I have partial measures of a HGS pipe and probably a standard somewhere, are you asking to see those numbers?

Forget the 35 we go to 36 and lost lots of hp
Here you got new exh.

[andreas]

I'll test it.
You built this in Engmod, or tested on track?
And it's for the powervalve yz85?

[dutchpower]

I'll test it.
You built this in Engmod, or tested on track?
And it's for the powervalve yz85?

Both track and dyno

[andreas]

Both track and dyno

Ok, great, looking forward to test it. How do you face it to the duct, it's smaller than 38mm right?

[dutchpower]

Ok, great, looking forward to test it. How do you face it to the duct, it's smaller than 38mm right?

You can make it bigger is also oke

[andreas]

I mean, the cylinder exit on the yz is close to 35mm, I believe. How do you join them?

[wobbly]

After 40 years of pipe building using Dynamation , then Mota , then EngMod I have never seen anything make good power with a 1.8* header , nor a 12*/30* tailcone ?
Sure its good to try things that have never been done before , but weird is still weird at the end of the day.
Its like " Stuffing " telling everyone our headers and diffusers should be 34%/68% - never seen one , never built one - why would I , the code says its shit every time.

[dutchpower]

After 40 years of pipe building using Dynamation , then Mota , then EngMod I have never seen anything make good power with a 1.8* header , nor a 12*/30* tailcone ?
Sure its good to try things that have never been done before , but weird is still weird at the end of the day.
Its like " Stuffing " telling everyone our headers and diffusers should be 34%/68% - never seen one , never built one - why would I , the code says its shit every time.

Make it better Wobb and help ( andrea ) maybe I can learn something after 50 years of making exh.

[wobbly]

Send the .pack to wobblywayne8@gmail.com.
Its impossible to optimize any pipe in isolation.

[andreas]

It's fine. Anyway I don't have the data.
Fitted v-force today, with positive report.

[porttiming124]

Hi there .
Why did you make them (pipe) in section rather than hydroform?

[andreas]

Simply, was never acquainted to that method.

[SwePatrick]

Forget the 35 we go to 36 and lost lots of hp
Here you got new exh.

Wow!
That is the most odd pipe i´ve seen.
I wouldn´t bother building that :(

[wobbly]

The only YZ85 pack I have is for a non PV engine used for flat track racing.
Here is the sim power for its pipe Vs the one shown here I said was weird.
The flat track pipe is already 9mm longer.

I could easily make the flat track pipe longer again to gain back the approx 1 Hp loss up the front side , but that wasnt needed for the application.
With some extra length it would easily match the others power, but with a longer length its up 6Hp @ 12750 and 10 Hp up at 13500.

So clearly its the design that is at fault.
The pipe shown , working back from the tuned length , has a header at 34.7% and a diffuser at 68%, so now I see the power characteristics you can understand why I said " Stuffing "
was on the wrong track , as is the pipe shown here.

[andreas]

Wobbly, can I buy this drawing?

[wobbly]

Only if I get to do it properly with your actual engine info in EngMod.

[andreas]

It would be a treat, but the bike doesn't belong to me, and the pipe is not prioritized to that extent.
I'll proceed to tinker along the same outlines as before. Maybe with a highly speculative parallell first third of the header, and possibly a second wide range pipe for heavy sand.

[dutchpower]

It would be a treat, but the bike doesn't belong to me, and the pipe is not prioritized to that extent.

Non pv bike std.engine and Odd Pipe

[dutchpower]

Changing crank / head / cdi curve and little on the cil. over 30 hp

[Frits Overmars]

Non pv bike std.engine and Odd PipePiet, seems like you could use some software updates:msn-wink:.
They're free, you know. Call me.

[wobbly]

I still come back to the fact that no one anywhere ever , I have seen , has published a proven pipe design with a 1.8* header at 34,7%.
Maybe its a thing that everyone has missed for 30 years .
I have close to 150 customer files in EngMod , it needs proving one way or another - but I am fully aware it may be very end use specific to the small YZ .
Same with the 12/30* rear cone.

[husaberg]

I still come back to the fact that no one anywhere ever , I have seen , has published a proven pipe design with a 1.8* header at 34,7%.
Maybe its a thing that everyone has missed for 30 years .
I have close to 150 customer files in EngMod , it needs proving one way or another - but I am fully aware it may be very end use specific to the small YZ .
Same with the 12/30* rear cone.

Out of interest how much time does it take to add in another pipe in the sim Wayne?

[wobbly]

If I have a well working sim and you give me the dimensions it would take 3 sips of single malt.

[Condyn]

Even with the crap transfer geometry of the old piston port air cooled twins I spend my time on, What has proved to work well on the engine dyno is 32/66 with a 3.5-4 degree header angle. I have built and tested dozens of pipes. Anything over 33% with a shallow header has simply not revved. The next batch we will be testing is even less header at 30/31% and longer diffusers 68/69% with shorter and steeper baffles. (CVT utilized engine)

On the chassis dyno and field testing there was another issue. We found the power to fall off relatively dramatically on the top of the run. Something is not in sync, * EDIT * possibly when the pipe temp climbs to a certain range. Or maybe the compression ratio is too high… It must be heat related one way or another.

[wobbly]

The long ( over 32% ) header length scenario with its reduced overev is easily seen and understood when looking at the depression values around BDC .
As the rpm rises the max depression point moves to the right , leading eventually to virtually nil depression before BDC. A short header starts the depression earlier in the cycle , thus keeps the leftward biased wave shape for longer.

In a CVT especially my opinion would be you don't want a long ( 68%) diffuser either , as this will naturally dictate shallower angles than is possible with a short ( 64% ) length - as always , tempered by the law of
diminishing returns.
In this case where you are never low in the power band , I would be looking at 29/30% - 64/65%.
Having a short header with a long diffuser makes the angle issue even more evident - thus is a classic mismatch for the end use.

Yes , a sharp power drop after peak may be affected by heat - too much com or to much advance ( high MSV, same effect ) due to more heat being transferred into the piston/water , than is dumped into the pipe at EPO.
An overly steep rear cone will have the same effect after peak as well - but a 3 angle setup makes it a lot easier to fine tune the peak vs overev dichotomy.

[Condyn]

Very Interesting Wobbly. Am I incorrect in assuming that with Virtually non existent inner radii in the transfer ducts that having steeper diffuser angles would make for even less trapping efficiency? I will try anything suggested.

Here is a log of a test pass I made. 500 foot drag race. The engine rpm is held constant within a couple hundred (yellow). The red line represents the shift curve of the jackshaft connected to the secondary clutch.
The orange line is pipe bulk temp in Fahrenheit which is a K type thermocouple in the center section of the pipe on the centerline. The blue line is cylinder head temp in Fahrenheit. As you can see the pipe temp climbs the entire way through the track and drops off when the throttle is shut where the CHT continues to climb after shutdown. A flat ignition was unfortunately used at the time.