ESE's works engine tuner

[F5 Dave]

. . Firstly get out of your head completely the lawnmower engines view of the world that the piston dropping increases the pressure in the case, and it is this that forces the flow thru the transfers.
Mr Villiers creations may have operated this way - not any modern 2T.
. . . .

Meh, I'm pretty sure my GasGas Trials bike made in '00 works entirely like that. There is a parallel pipe from head to the first muffler section. ok it only puts out about 9hp, but it is surprisingly torquey (hehe I love using that word).

[rgvbaz]

[QUOTE=dinamik2t;1130292267]Attachment 260684




G-K: Tfr pressure below 1. No flow?



QUOTE]

No, there will be flow because there is a diffential pressure between the transfer port and the cylinder, even though the transfer pressure is below a pressure ratio of 1. With the transfer pressure ratio being greater than the cylinder, the direction of flow will be into the cylinder.

See pic below. These are from Post2T in the thermo and gasdynamic traces in the plot options tab.

The Ptr (transfer) Pex (exhaust) and Pcyl (cylinder) pressures respectively and Mtr is the mass flow of gas at the transfer port 0 = no flow +ve number = flow into cylinder -ve number = flow back into the transfer port.



Note. the mass flow doesn't reverse exactly when the cylinder pressure becomes greater than the transfer pressure, it is shortly after (I thinks this is to do with the left and right pressure waves)

[Frits Overmars]

I'm pretty sure my GasGas Trials bike made in '00 works entirely like that. There is a parallel pipe from head to the first muffler section.

And I'm pretty sure the length and diameter of that parallel pipe were optimized to the millimeter.
Every duct in an engine plays a gasdynamics role, whether you want it or not, so you better make use of it.

[Frits Overmars]

.....the mass flow doesn't reverse exactly when the cylinder pressure becomes greater than the transfer pressure, it is shortly after (I thinks this is to do with the left and right pressure waves)

I thinks you should think again, rgvbaz. Pressure differential does not equal flow; it equals acceleration. If there is a lot of inertia in the mass flow (a long gas column and / or a high flow velocity) a negative pressure differential will spend a lot of time slowing that flow down to zero before you will see the first sign of flow reversal.

[rgvbaz]

I thinks you should think again, rgvbaz. Pressure differential does not equal flow; it equals acceleration. If there is a lot of inertia in the mass flow (a long gas column and / or a high flow velocity) a negative pressure differential will spend a lot of time slowing that flow down to zero before you will see the first sign of flow reversal.

I guess I do need to thinks again then, Frits. What you say makes perfect sence.

I had did have a quick look at the mass flow in the exhaust pipe at a couple of transducer points - it does seem that the sim calculates the mass flow from the differnce in the LH and RH wave, maybe it doesn't consider inertia?

[TZ350]

The big thing to come out of the last ten pages seems to be that insufficient blow down time area can lead to over heating by having excessive hot exhaust gas entering the transfer ports and over heating the engine.

… a single exhaust port there? I can hardly imagine the blowdown time.area will allow for more than 9000 rpm. That means: any more revs and the hot exhaust gases will blow down into the transfer ducts, heating up the cylinder quite effectively. If that is the case, not even water cooling would give you reliability.

EngMod2T is an excellent design tool. But I use a different approach: my sim calculates the blowdown STA that is required if you want to avoid any exhaust gas entering the transfers.You cannot keep an engine like that thermally sound if you allow any exhaust gas to heat up the cylinder, hence the different starting point in my STA calculations.
Granted, if the engine produces less power, you may get away with some blowdown into the transfer ducts. I merely tried to indicate that you can combat cooling problems by paying attention to the blowdown STA.

In a real engine the exhaust gas defines how much time.area it needs to leave the building. If the transfer ports open before the cylinder pressure has fallen below the scavenging pressure, the exhaust gas will regard those open transfers as yet another set of exhaust ports and it will enter the transfer ducts. That will steal some of the transfer time.area.
Then, when the cylinder pressure has dropped sufficiently, those exhaust gases have to be expelled from the transfer ducts; that steals some more transfer time.area before the real transfer of fresh charge can commence.
So when an engine revs too high for the available blowdown time.area, it is the remaining available transfer time.area that suffers doubly. That is also the reason that power drops rather steeply past its maximum.

The raw numbers as presented in the STA calculations take no account of possible backflow issues with insufficient blowdown.
One thing that cannot be quantified is how much the heating effect of the blowdown reverse flow is able to be dissipated by the cooling fins.Rob says it was fine at 28 Hp.
Only way to see if the engine is now on the limit is to thrash it do death on the dyno, emulating as far as possible the air flow regime with a fan, and see if the power fades dramatically.
A direct drive KT100 will fade 3 Hp in 18 after 4 pulls from 6,000 to 16,000 in 9 secs,change the pipe and loose a couple of that peak Hp and you can run all day with no fade at all, but still see the same 620C on the egt.

I was going to try and format all the separate rod and piston stuff onto one Excel sheet when i get some time and enthusiasm.

http://http://www.samarin.net/?productos
http://www.pvlsverige.se/vrm/index/index22.html
http://www.mxcomposites.com/con_rod.php
http://www.connectingrod.com.tw/ktm.htm
http://www.pro-x.com/downloads/Technical.pdf
http://www.kevinbreedonracing.co.uk/...ts_conrods.asp
http://www.connectingrod.com.tw/honda.htm
http://www.samarin.nl/webshop/index....ewCat&catId=32
http://www.tkrj.co.jp/
http://findebookee.com/c/connecting-rod the one is capt

On the original post Husa has now placed a spread sheet with rod dimensions.

Some of it is on a public forum: http://www.pit-lane.biz/t117p246-gp1...es-aprilia-rsa .

… essential factor is inertia. Even with ample STA and a healthy pressure ratio a stationary gas column needs time to get up to speed. The longer and heavier the column, the slower it gets moving.
(when talking about intake ducts you might argue that such a sluggish column will give a useful ramming effect later on, but I would say that this is just an attempt at the end to make up for something that went wrong at the beginning).
-------------------------------------------------------------------------------
Gordon Jennings certainly did a lot of good with his easy-to-read articles. But he created one misconception that is festering until this day, with his translation of the SAE-papers of Yamaha's Naitoh and Nomura into 'tuner's english'.
He extracted specific time*areas and claimed them to be the optimum values for a two-stroke. On the scavenging side he was as right as makes no difference, but on the exhaust side it was quite another story.
Naitoh and Nomura just stated their findings; Jennings concluded that specific exhaust time*area should be what Yamaha had been using. But Yamaha had by no means found a gasdynamic optimum; they just had gone as far as the quality of their piston rings allowed them to do. And had they thought of using auxiliary exhaust ducts (first seen in their present form in the 1971 Jamathi engine), they would have made a quantum leap.
Another point of criticism is that Jennings emphasized exhaust time*area and almost neglected blowdown time*area.
----------------------------------------------------------------

Nowadays an engine needs a large crankcase volume (the Aprilia RSA125's is 675 cc at TDC), all the port area you can cram into the cylinder circumference, good ducts for efficient flow and directional control, an exhaust that sucks and blows hard at the appropriate moments, and cooling, cooling, cooling.

Re Blowdown STA numbers and the effect they have.
Firstly get out of your head completely the lawn mower engines view of the world that the piston dropping increases the pressure in the case, and it is this that forces the flow thru the transfers.
Mr Villiers creations may have operated this way - not any modern 2T.
When the transfers open, there is more pressure above the piston than there is case pressure in the transfer duct.
This gives rise to the alarming notion that when using staggered ports, the one to open first has so much backflow that it takes ages to recover, thus it has inflow last.
The area available in the Ex from the time the port cracks, down to where the transfers open, sets the amount of combustion pressure that is lost down the duct, and thus the amount of
positive pressure ratio across the open transfers ( and for how long this lasts ).
We can have NO FLOW until that positive pressure ratio is reduced to the point where we have more case pressure than cylinder pressure.
There are two ways to do this - lift the case pressure and or lower the cylinder pressure.
In a modern engine the case pressure is only rising very slowly due to the piston dropping, but what we do have is the pipe diffuser action, that started with the high pressure front ripping
out the opening Ex port - then entering the expanding pipes front section.
As the piston approaches BDC the Ex port is starting to suck the chrome off the proverbial towball,dropping the cylinder pressure ratio dramatically, and it is this that forces the bulk flow into the cylinder.
If the blowdown is set correctly for the power needed within the rpm band we want, then the recovery time from the unavoidable transfer backflow at the opening point, is such that we get the correct
amount of inflow to be trapped above the piston, thus creating the conditions for the correct amount of combustion pressure after the spark event.
It is this set of conditions - all revolving around the blowdown pressure, that ultimately creates how much combustion psi is developed - this creates torque, and it is this combined with rpm that creates POWER.

Crankcase pumping only serves to start the engine; once it is running in the power band you can forget all about pumping efficiency.

Supercharging by definition is a method to increase the efficiency of an engine by using an external device that creates a higher delivery ratio, than that able to be achieved by the swept volume alone.
This can use energy within the Exhaust gas flow as is done by a Turbocharger.
It can use crank power to drive a pump, that creates more power at the crank than it consumes - a Supercharger.
Or - you can use sonic wave action in a divergent/convergent pipe, that uses that energy to evacuate and then refill the cylinder to a higher level than the swept volume alone could achieve - a Sonic Supercharger.
Next is Chemical Supercharging - where the fuel contains excess oxygen than that contained in the swept volume of air.

There are other link/post collections on most other decade pages ......

[husaberg]

Nowadays an engine needs a large crankcase volume (the Aprilia RSA125's is 675 cc at TDC), all the port area you can cram into the cylinder circumference, good ducts for efficient flow and directional control, an exhaust that sucks and blows hard at the appropriate moments, and cooling, cooling, cooling.

I kind of like this one the best.

I found the Helmoltz Blues on the pitlane thread and yes the search function was not that great. The KB one is pretty good as long as the keywords are carefully chosen.

This was posted by Kel a fair ways back.Its off the Pitlane thread.

Frits Overmars
Sujet: Re: [GP125] Caractéristiques Aprilia RSA Mer 8 Déc - 13:36
In theory enclosed cranks are good. Jan Thiel did some experiments at Aprilia with a kart engine that had its reed valve at the front: the incoming mixture had to move against the direction of crank rotation. And although the crankcase stretched over the crank webs, reversing the direction of rotation brought another HP. So the crankshaft does have an influence.
But in practice, if you reduce the distances between crankshaft and crankcase walls to less than 1 mm, the viscous friction of the mixture between the surfaces really costs power at high rpm. And if you make the clearances so tight that lubricating oil can no longer reach the big-end and crankshaft bearings, it will also cost engines
Another negative aspect: any volume with a narrow 'entrance' between the crankshaft and crankcase surfaces acts as an hydraulic damper on the Helmholtz-resonance in the crankcase.
Aprilia has avoided this by making the space between the crank webs as wide as the big-end bearing. As a result the crankcase volume of the 125 cc RSA engine at TDC is about 650 cc, so the exhaust pipe really has some volume to breathe from.
So much for the fairy tale of high crankcase compression

Ps twice now you have referred to this and the pitlane forums as being open public.
Does that mean there is a invitation only 2 stroke tuners thread?

[wobbly]

You are right about the Gas Gas engine spec.That sport has a whole different dialogue of its own to describe the performance of the torque curve needed to jump rocks in a single bound.
The grunt ( small amount not withstanding ) has to be rising and falling at exactly the right time to give amazing control of the rear tyres force on the ground.

[Frits Overmars]

...twice now you have referred to this and the pitlane forums as being open public. Does that mean there is a invitation only 2 stroke tuners thread?

You must have a long-time memory like a goldfish, Husa. Two days ago I wrote:
"Some of it is on a public forum: www.pit-lane.biz/t117p246-gp1...es-aprilia-rsa . But most of it is not. And I am not even at liberty to reveal the forum's name".

EDIT: On second thought that may have come out a bit harsh. I did not want to insult either you or the goldfish.

[jasonu]

You must have a long-time memory like a goldfish, Husa. Two days ago I wrote:
"Some of it is on a public forum: http://www.pit-lane.biz/t117p246-gp1...es-aprilia-rsa . But most of it is not. And I am not even at liberty to reveal the forum's name".

EDIT: On second thought that may have come out a bit harsh. I did not intend to insult either you or the goldfish.

Are they chocolate goldfish? I know Husa has a fettish for those...

[Grumph]

You must have a long-time memory like a goldfish, Husa. Two days ago I wrote:
"Some of it is on a public forum..... But most of it is not. And I am not even at liberty to reveal the forum's name".

EDIT: On second thought that may have come out a bit harsh. I did not want to insult either you or the goldfish.

He lives on the wet west coast Frits - so besides having webbed feet, he can probably breathe underwater too...

Hmm - a secret think tank of two stroke tuners....did they do the study on the long term memory of goldfish ?

[husaberg]

You must have a long-time memory like a goldfish, Husa. Two days ago I wrote:
"Some of it is on a public forum: www.pit-lane.biz/t117p246-gp1...es-aprilia-rsa . But most of it is not. And I am not even at liberty to reveal the forum's name".

EDIT: On second thought that may have come out a bit harsh. I did not want to insult either you or the goldfish.

And who say's the Dutch have no sense of humor?
Ouch my goldfish is indeed a little miffed by the comparison as well, indeed he has crossed you off his Christmas card list .


The first time was this below er 6 months ago at first i thought it was just rhetoric but then your second time? 2 days ago.

I agree with Wobbly (I usually do): there is no money in paper books on two-stroke technology (there is little money in paper books period, unless you happen to write Harry Potter stories). But you'll find a lot of present-day info in forums.
ESE's works engine tuner is a good example, and of the numerous other forums that are 'open to the public' I would recommend www.pit-lane.biz. It's French-based, but yours truly and Jan Thiel are allowed to write in English (and I post all my photos in Dutch without anyone noticing).
A good starting point would be here: http://www.pit-lane.biz/t117p246-gp1...es-aprilia-rsa.

Reading through the above posts my eye fell on this remark from Wobbly, talking about reeds versus disks:
First of all, thanks for the flowers, Wob (like I just said, I usually agree with mr. Wright).
Second: it should read Jan and Frits, not the other way round; Jan did much more than my humble self in making the two-stroke so suppreme that it had to be put down by the Honda-Dorna combination.
Third: I would not say that a Honda reed valve engine kicked Aprilias arse. The Aprilia riders did that all by themselves, stealing points from each other and shooting each other off. Not even Honda-driver Hiroshi Aoyama would dispute that the Aprilias were faster.

now i may have a Carp like memory, but i do remember this.

You are right, Husaberg.
O, and one more thing, TZ350. Fritz is German. I am a Dutchie and I spell my first name with an s .

He lives on the wet west coast Frits - so besides having webbed feet, he can probably breathe underwater too...

He also doesn't need irrigate either, goes to the lakes or rivers and Tasman sea often and enjoys watching, while his grass grows all year around without any snow on the ground or nor wester's and the ground has been virtually vibration free for 30 odd years.
He also may get paid a wet weather allowance as well, yet not have to work in the rain .
he also lives surrounded by a lush subtropical rainforest that millions of people come here especially to see this unique beautiful scenery every year.
The world class hunting fishing and outdoor recreation all make living on the west coast so frustrating. as well not to mention the overcrowding issues with my closest neighbor a 5 minute walk away.
So yeah us coasters sure are odd creatures

[Grumph]

So yeah us coasters sure are odd creatures

Hey, i was nice and didn't mention the extra toes so prevalent amongst coasters...

The West Coast is only temporary anyway - when the alpine fault goes, so does that coastline.

[husaberg]

Hey, i was nice and didn't mention the extra toes so prevalent amongst coasters...

The West Coast is only temporary anyway - when the alpine fault goes, so does that coastline.

You mean that alpine fault that was created in the southern alps the mountain range that divides the West Coast from the East coast.One of the many faults that run of the two plate boundaries.
Oh those Alpine faults that are equally dispersed between Me and er...... You.
Also is that a volcano beside you there.

PS that extra toe is bloody handy, I understand it's almost like having an opposable thumb

[TZ350]

Do I see a single exhaust port there? I can hardly imagine the blowdown time.area will allow for more than 9000 rpm. That means: any more revs and the hot exhaust gases will blow down into the transfer ducts, heating up the cylinder quite effectively. If that is the case, not even water cooling would give you reliability.

I can hardly imagine the blowdown time.area will allow for more than 9000 rpm. That means: any more revs and the hot exhaust gases will blow down into the transfer ducts".

My sim calculates the blowdown STA that is required if you want to avoid any exhaust gas entering the transfers.

Your screenshot shows a BMEP of 11.4 bar @ 12,500 rpm. That is, like you say, achievable and believable. The Aprilia RSA also develops its maximum BMEP at about 12,500 rpm, but its value is almost 50% higher.

You cannot keep an engine like that thermally sound if you allow any exhaust gas to heat up the cylinder, hence the different starting point in my STA calculations.

Granted, if the engine produces less power, you may get away with some blowdown into the transfer ducts. I merely tried to indicate that you can combat cooling problems by paying attention to the blowdown STA.

In a real engine the exhaust gas defines how much time.area it needs to leave the building. If the transfer ports open before the cylinder pressure has fallen below the scavenging pressure, the exhaust gas will regard those open transfers as yet another set of exhaust ports and it will enter the transfer ducts. That will steal some of the transfer time.area.

Then, when the cylinder pressure has dropped sufficiently, those exhaust gases have to be expelled from the transfer ducts; that steals some more transfer time.area before the real transfer of fresh charge can commence.

So when an engine revs too high for the available blowdown time.area, it is the remaining available transfer time.area that suffers doubly. That is also the reason that power drops rather steeply past its maximum.

This is very interesting as you can see the steep drop off in the 31hp graph, and at Taupo after looking at the speed trap times and gearing, the bike was running at 13,000rpm up the back and for a good part of the front straight, well in the exhaust gas down the transfers region.



The engine did not seize on full throttle running flat out, but after several down changes, when the throttle had been closed for a bit, maybe the cooling was marginal and when the cooling from the MJ fuel stoped, the engine stoped.

So what to do? an alloy sleeve with large tripple ports, not for power but for better thermal reliability ...