ESE's works engine tuner

[Frits Overmars]

So, I have a pile of cylinders I just finished ported that I am about to send off to Millenium Technologies to strip out the stock chrome bores and re-plate with Nikasil. Happy days
I just got off the phone with the guys at Millenium and they tell me they can do "round" port edges or "45 degree" port edges, with a defined profile view drawing to establish the desired chamfer geometry for the work order.
I have always done this myself, and I try to go for a nicely "rounded" edge with a radius of ABOUT 0.6 - 0.8mm for all port edges.
Some recent light reading has skimmed across the notion that the transfer port edges should NOT be chamfered because the chamfered edge will cause the incomming transfer stream to spread/spray out like a fan-nozzle on a garden hoze instead of maintaining the intended tragectory from the transfer port axial/radial aiming angles.
Instead, the transfer port edges should "just" be de-burred with the edge "broken" but not chamfered.
Given this idea;
How would you go about defining that on a work order?
Should I just tell them NOT to touch the transfer port edges and do it myself?
Perhaps put "de-burr only/ no chamfer" on the work order?
I have the rexcut cotton mounted points that Wayne recommended for port edge chamfering of Nikasil cylinders without chipping, but I would rather let Millenium do the work.
How about the exhaust port edge chamfer?
What radius size chamfer should I be calling out for the exhaust port of a 52mm jug?
-70% width single exhaust port with FOS Concept port shape

Tell them NOT to touch the transfer port edges no matter what.
Jan Thiel once got a set of race-winning cylinders back from replating, that had to go straight into the bin: all ports chamfered in spite of strict orders not to do, and all power irretrievably gone. Needless to say those were the last cylinders ever to go to that replating firm.

The exhaust port top and bottom edges should be radiused but the side edges should not be touched but only deburred, which you can do yourself after replating.

I give the exhaust top edge a radius of 5% of the stroke which is a fair bit more than you proposed. It does alter the exhaust timing so you must that take into account before shaping the port.


The drawing below shows the safe port shape for the benefit of piston longevity.

[wobbly]

My advise is to demand they dont touch the cylinder at all, and do the edge break radius with Rexcut on the transfers prior to plating, this then means you can remove the flashed chrome inside the port
and do the same edge break on the chromed corner.
The Exhaust port as Frits says only needs the edge breaking on the vertical sides, before and after plating.
The ring guiding top/bottom chamfers should also be done before chrome, and I do a 15* angle around 0.5mm high in the alloy that is redone to around 1/2 that height with a Rexcut radius on the bottom timing edge after plating.
Using the FOS port shape ameliorates many of the issues encountered with port edge chamfers, so its then nowhere near as critical as many believe.

[Condyn]

Storbeck, that was a good thought process, however it drops both et and mph when I go one leaner on jet from my happy egt zone. I had to study my notes and logs again because I thought for sure you had it. We also cannot forget the tell tale pop on the warm up stand when I go too lean.

Wobbly, thank you for the advice with minimal information on my tune. I will try the timing advice after my next race as I have to move the stator. This time I will mark it per degree so I can do it in the field on the fly. Here is a photo of my wash from the last test session two weeks ago where I set my personal best ET. At the end of the run I have to turn around and blip back to the staging area so take that into consideration. It is a 4 transfer, single exhaust, piston controlled inlet turd.

[bad'rule]

*But air cooling was just not up to handling the waste heat from the higher HP. *
Hiya
Tz, have you thought of adding JetCool on them.Later Suzukies Cubs bike they all having these feature on their engine. It's a fan being skru to the mags.The air stream to cools those cylinder and the end had two holes aim to lower case of the engine.
You may search for suzuki RC 80,100 or the last of those Cubs with upward cylinder is RU or RG 110 sport, RGV120 .
Here's how their Mags cover looks

[wobbly]

Condyn, the pop scenario is what KZ Kart tuners have used for years to " tune " their engines as to most all, EGT is voodoo shit.
The engines normally run to about 14500 on track, and in the pit, when the throttle is nailed and held open, if the main is correct it will hold 15500 popping like mad.
This practice has now been banned by the CIK due to " noise ".
So I think you are seeing the same thing, if you are referring to " popping" at full throttle.
But as I have explained a thousand times, EGT tells you everything you need to dial in to the edge of deto.

[Viking]

As a new member to this forum I start with a short presentation.
I tuned racing engines and built expansion chambers for about 50 snowmobiles and MX-bikes some thirty years ago.
Then work-life get in the way...
Now I´m aiming for retirement, and a return to two stroke tuning.
Started to learn simulation with EngMod2T, and became addicted, so it´s very hard to stop.
But the snowmobile must out on the racing track, therefore the simulation has to end.

What do Wobbly say?
Can I stop the simulation and be satisfied,
or is there some improvements that can be done?
(See attached picture of the results.)
The engine is based on a fan cooled 2-cylinder 400cc unit I built.
Back in the days it had 83hp on the dyno.

[F5 Dave]

That shit used to piss me off. You're trying to think/relax/fix your bike and some kun is revving the tits off his cold kart engine whilst on a stand with the wheels going 100mph at face level to junior wandering around the pits (it's a family affair) ready to rip it off and spit it to Invercargill.

[ApolloMotoMoto]

Tell them NOT to touch the transfer port edges no matter what.

My advise is to demand they dont touch the cylinder at all

Somehow I kind of knew thats what you were going to say, but I do sincerely enjoy an extra bit of confidence when I get the chance to hear it from the horses mouth.

Thank you for the recommendations, I shall study and implement them!

The port-edge chamfering I got back from PowerSeal was... attrocious, in a word. PowerSeal also said they could not hone my cylinder as there was too large of a gap between the skirts on the sides where the transfer feeds are.... the stones were "jumping around" when the hone got down to the area where the side gaps in the skirt are.

Hence my move to Millenium, who, after explaining the honing issue to them seemed to understand that my cylinders would likely be a problem for a 4 stone mandrel, but they said they have an in-house built 8-stone mandrel that will work for my bore size, and they are confident they can successfully hone my cylinders.

The drawing below shows the safe port shape for the benefit of piston longevity.

Using the FOS port shape ameliorates many of the issues encountered with port edge chamfers, so its then nowhere near as critical as many believe.

It took me a little while to fully understand how to implement the geometry from the picture as a function of my 52mm bore size (which I am assuming is close enough to the bore size those values are "tuned" for that I should be pretty safe), but I have been using this shape in any cylinder I port for nearly 10 years now. Originally I literally just copy-pasted the image from the drawing and scaled it to fit my application, but I now know how to properly build the "multi-radius" shape for a given application.

I have been cutting the exhaust ports to 70% width using this shape for exactly as much time and have yet to have a single "ring snag" event in any engine I have ported. Which is a testament to the statements above, the shape itself largely ameliorates ring-snag worries at 70% port width.

Thanks again for all the sharing of information.


This place is a hidden gem among the near infinite layers of "the internet".

[ApolloMotoMoto]

I give the exhaust top edge a radius of 5% of the stroke which is a fair bit more than you proposed. It does alter the exhaust timing so you must that take into account before shaping the port.

...in all cases?


I have bumped into this idea a few times, but it recently came up on the EngMod2T users group:

Has anyone tested/documented and created formulas associated with radiusing the top edge of the exhaust port? Power range and HP gains? I have found a lot of benefit on an engine I did recently.

Wayne replies...

Jonathan Raulo , you have to realize this workaround was developed by Jan to ameliorate the negative effects of a flawed pipe design ( mandated by his boss ) that lacked top end power.

If you look at the raw STA numbers of that Aprilia the transfers were around 10% ahead of the Exhaust Blowdown capability, and Jans method of increasing the main ports Cd was an elegant solution at the time. But the natural down side of that **gradual ramp up** of wave amplitude at EPO would be to reduce the depression efficiency at BDC, where it really matters.

I have discussed this with Jan, and tested the radius in a KZ, the result being that I now believe that if you found an advantage with the radius, you were seeing a swings and roundabout effect of one element partially counteracting the other. It actually indicated the engine was lacking Blowdown.

The much more effective fix is to do something definitive about that issue, not use Jans band aid, but genius approach.

The back and forth discussion continues, I will share some more of Wayne's points:

In the Aprilia, as I noted above, the engine was Blowdown limited by around 10%, and as soon as this was helped by the radius increasing the port Cd - power went up.

I tested the idea in a KZ cylinder ( 25* roof ) that had won the Euro and World Titles a couple of years ago. This engine was always Blowdown limited, and the radius added just over 1Hp from the upper front side into the overev. Grinding out the radius and lifting the port to where that radius started , added another 1.5Hp.This made the Blowdown and Transfer STA all but equal. It now lacked the same amount of power down at 10,000 rpm, but in the Aprilia with a PV on the main port this would not have happened.

What do I mean by **gradual ramp up** - this describes what occurs in the EPO phase when the timing edge is radiused - the area increase gradually.

The total energy in the wave of a radiused or sharp timing geometry is the same, but the radiused edge waves amplitude is reduced, and smeared out in time.

This exact same thing occurs when in the past tuners have tried lifting the Aux up incrementally. Peak power rises, at the expense of band width right up to the point where the are coincident, then power drops everywhere. This is due to the two effects of lower amplitude time smearing plus the huge difference in path length of the main and Aux wave fronts.

Again I reiterate, the radiused timing edge was a genius band aid by Jan, but actually correcting the fault ( lack of Blowdown ) makes more power in a fully optimized scenario. As Jan said he now regrets not knowing the STA numbers as his first reaction would have been to lower the transfers.

So;

Is the 5% of stroke radius that Frits just recommended exactly what was done in the Aprilia RSA engine?

Frits:

Do you use this radius after you have "balanced" the blowdown and transfer STA numbers, or do you have to "account" for the blowdown boosting effect of the radius in order to properly balance the blowdown and transfer STA when using a radius timing edge?

How do you calculate the Blowdown STA increase that will result from the radius?

Given the "story" of the radius as presented by Wayne above, why do you continue to use it?

Wayne:

What are your thoughts on implementing the radius timing edge in my case?

I have a single exhaust port cylinder that is pretty severly blowdown limited because of this.

I have the ability to create plenty of Transfer STA to balance with the blowdown STA I can get with a 70% single port using the FOS 'multi-radius' shape.

IF I were to use the radius, it would seem to me that I could "cheat" a little bit more Blowdown STA out of my single port without making it physically wider or taller.

If I were to then tweak the transfer side STA to balance with this "radius boosted" Blowdown STA number, I am now "ahead of the game" compared to a sharp timing edge port of the same height and width with less Blowdown STA, and thus less Transfer STA to balance with it.

Oops! -I almost forgot the impact of the "wave energy smearing" effect.

So, what do you think Wayne, does the "smeared" wave energy of the radius timing edge negate the net Blowdown/Transfer STA improvement from using the radius?
-assuming each one has a pipe designed to "complement" their respective regimes
-and assuming in both cases the ACTUAL blowdown FLOW STA is in balance with the Transfer STA

[Frits Overmars]

Is the 5% of stroke radius that Frits just recommended exactly what was done in the Aprilia RSA engine?

Pretty much. The exhaust top edge radius in the RSA (and in the latest RSW version) was 3,5 mm but it did not blend tangentially into the bore, which would have been rather challenging for CNC programming due to the elliptical shape of the port and the curvature of the bore.
Instead, this top edge radius center was slightly offset towards the cylinder bore center, which had the same effect as a fully-tangential radius of 2.5 mm.

Do you use this radius after you have "balanced" the blowdown and transfer STA numbers, or do you have to "account" for the blowdown boosting effect of the radius in order to properly balance the blowdown and transfer STA when using a radius timing edge?

If I were to balance the angle.area values before applying the radius, applying the radius afterwards would upset the balance, so....

How do you calculate the Blowdown STA increase that will result from the radius?

Calculating the blowdown angle.area is both a geometric and a gasdynamical challenge. I apply not only a timing radius to the exhaust port top edge with its elliptical shape, but also a timing radius to the piston top edge. These radii affect the blowdown cross-flow area but also the flow coefficient, which cannot be taken into account in EngMod.
The initial supercritical blowdown flow between the port edge radius and the piston edge radius experiences a partial DeLaval effect and the resulting energy conservation, compared to flow through a sharp-edged orifice, more than compensates the “smearing effect” that Wobbly refers to.

Given the "story" of the radius as presented by Wayne above, why do you continue to use it?

Your question suggests that I started using the exhaust top radius after Jan had applied it. But Jan started using that solution in the early 2000s if I remember correctly.
I applied a timing edge radius to the piston in 1963 when I was 15 years old because it was the easiest way to modify the transfer timing with the very limited tooling at my disposal, and when I was lucky enough to get my hands on the book below a few years later, I also started applying a top edge radius to the exhaust port.

[Condyn]

Condyn, the pop scenario is what KZ Kart tuners have used for years to " tune " their engines as to most all, EGT is voodoo shit.
The engines normally run to about 14500 on track, and in the pit, when the throttle is nailed and held open, if the main is correct it will hold 15500 popping like mad.
This practice has now been banned by the CIK due to " noise ".
So I think you are seeing the same thing, if you are referring to " popping" at full throttle.
But as I have explained a thousand times, EGT tells you everything you need to dial in to the edge of deto.

It is exactly as you described. Popping while over revving on the warm up stand with no load. I actually no longer do this anyway because it pisses everyone off, but I have stayed away from finding that EGT since my last experiences with it. I do not see EGT as voo doo, but I understand you perfectly.

[jonny quest]

Condyn, pipe wall temperature is a big tuning issue on snowmobiles.

They don't get hot quick enough in a drag race compared to dyno tuning.

We usually clutched 200rpm lower on the track compared to dyno.

[wobbly]

Apollo, as stated in one of my replies the STA numbers of the RSA, as calculated off the raw timing numbers in EngMod showed that the Blowdown was down near 10%
in direct comparison to the transfers.
Jan adding the radius gave a good increase in power, so one could assume the increase in Cd due to the sort or radius the RSA actually had, would be close to that 10% number.
Jan's reaction when this was discovered, was to lament the fact that he never tested the engine with lower transfers.
Again , in the sim, if the main Exhaust port is lifted to what is effectively the beginning of the radius timing, close to 200* duration, the numbers are very close to alignment.
Frits is also right about the synergistic effect of a port radius and a piston timing edge radius - this is another level of sophistication that obviously works, in theory and in practice
as he has tested and proven this.
Then you have the logistical nightmare of shaping the head squish band to suit this.

But it is something that you must do your own due diligence on.
Having the piston radius right around the piston causes an issue with the exit flow adhering to this shape over the boost port, and creating short circuiting when the pipe efficiency is high.
In my testing the timing edge radius gave a good increase all the way up to peak, but lost in the overev.
You can fix this by deleting the radius over the boost, ie CNC cutting it with a reflex radius tool, or using a vertically set dividing head, and then adjusting the boost timing to suit, and or lifting
the boost port floor height to prevent flow adherence at and around BDC.

EngMod is a single dimensional code so this is an area that cannot be simulated effectively.

[Flettner]

What conclusion did 'we' come to about the exhaust dam? How far can one go?

[wobbly]

Viking , may I suggest you join the EngMod 2T Users Group on FB, I am an Admin so can approve you instantly.
Looking at your sim screenshot, I see a few things.
It has very good superposition, but to me it could maybe be improved by increasing the diffuser depression early in the cycle below zero pressure ratio.
This can be achieved with a shorter/steeper header, and a steeper first diffuser section - these adjustments are seen as improved peak and overev power.
The rear cone plugging amplitude is impressively high, but a little narrow in width.
Maybe a slightly longer tailcone, with increasing multiple angles would help.
Is that rpm at peak power ?