ESE's works engine tuner

[wobbly]

Polcat - I can confirm that simply extending the Aux ducts out thru the spigot to the header interface does nothing.
The combination of better blowdown flow is offset by the increase in duct volume ( and the exit area ratio ) to the point that
no power is gained.
TM did this 10 years or more ago , and the concept failed miserably.
Its only when I introduced the 75% area reduction concept that the huge increase in power became a reality for the 3 port design.

[Frits Overmars]

Thanks, Wobbly. I don't believe anyone in the snowmobile world has taken the auxiliaries out as far as Jan and you have. So the best way forward in your opinion would be to develop the auxiliary exhaust before anything else...

When working on the auxiliary exhaust ports, keep this in mind Steve:

You may vary the angle of maximum overlap by varying the piston pin height in the piston, so that the overlap occurs when the pressure difference between exhaust and transfer ports is minimal. But completely closing the piston skirt is preferable in any case.

[TZ350]

maybe later i can add better cooling methods if needed. also i use methanol which is a bit different than petrol,

I have very fond memories of Methanol.

I ran a race TR250R Suzuki fitted with air cooled RD250 and later RD350 cylinders running on a 50/50 methanol/acetone blend. The problem was not cooling but rather getting the engine warm enough to evaporate the fuel properly.

You can easily over cool a methanol two stroke engine with just the fuel alone. When that happens the mixture looks lean but adding more fuel only makes things worse. The trick is to worm the engine up by blending the fuel to something that takes less heat out of the motor.

Later I was involved with a TZ750 based TQ racer on methanol. The engine was fitted with one TZ350 cylinder block and one TZ250 cylinder block to meet class capacity rules. The class also called for air cooling so the trick was to discard all the water cooling stuff and cut big holes in the outer skin of the water jackets so air could circulate around the inner cylinders for air cooling plus air cooled cylinder heads. That and methanol was enough cooling for long races of 25 laps or so.

Your little radiator might be to big unless you are running a thermostat. Even then the motor may be over cooled by the methanol and you will need to blend something less cooling with it. For my air cooled RD engines I used acetone for blending because its latent heat of evaporation is less severe and it has a very high octane rating.

The proper "Exhaust Tuned Length" is considerably shorter for a methanol engine too. Calculations have to be based on the slower wave speed through the much cooler methanol fog.

[peewee]

Your little radiator might be to big unless you are running a thermostat. Even then the motor may be over cooled by the methanol and you will need to blend something less cooling with it. I used acetone because its latent heat of evaporation is less severe and it has a very high octane rating.

The proper "Exhaust Tuned Length" is considerably shorter for a methanol engine too. Calculations have to be based on the slower wave speed through the much cooler methanol fog.

ive got two different styles of thermostats i can try. one is a bypass type that i got from someone around here. flettner maybe?. the other is nonbypass from a ktm dirtbike. about the pipes. ive been in contact with arlen from led regarding drag pipes. once i send some photos and measurments of the chassis and cylinder configuration. hopefully do that this weekend

[TZ350]

.

I love that you are working with Methanol and are very interested in the results.

I forgot to mention the crank oil seals. With my acetone methanol mix I left the oil seals in a sample jar with some of the 50/50 mix. The Suzuki ones seemed fine but Yamaha ones with the Teflon lip swelled up. They went back to their normal shape if they were left out for a few days.

The 50/50 mix was also hard on the lining of the Suzuki rotary valve covers, it loosened the bonding glue holding the lining on. I now use Kawasaki covers that don't have the anti friction lining.

I never tested it but I would be suspicious of composite rotary valve blades and fiber glass or carbon fiber reed valve's, best to use metal blades if you have acetone in the mix. Also if you have a rubber tipped float needle then I would check what that looks like after soaking it for a while too.

[shnaggs]

Frits, in regards to your port exit angle calculator, what does ATN stand for?

[Frits Overmars]

ATN stands for Arctangent. It is the counterpart of the Tangent function.
Example:
the tangent of 25 degrees is 0,4663077: Tan(25)=0,4663077
the arctangent of 0,4663077 is 25 degrees: Atn(0,4663077)=25
You may find the arctangent mentioned here: https://en.wikipedia.org/wiki/arctangent and in my Pisa-story:

[wobbly]

THere is one intermediate step available brefore having to use using pin plugs.
The exit angle shape of the Aux duct rear wall can be made shallow, to reduce the cavity connecting to the pin.
This makes more power ( and is easy enough to tune ) than a non overlapping rear wall , with the optimum angle.

[peewee]

whats some of the ways people have used to plug the pin hole ? i really havent put much thought into it yet but i have no plans of using shallow rear aux walls. i wonder if some cork thats 10-20mm shorter than the pin then cap the ends with high temp fipg like threebond. but maybe the superfast start and stop of the piston might cause it to compess and work loose

[Haufen]

THere is one intermediate step available brefore having to use using pin plugs.
The exit angle shape of the Aux duct rear wall can be made shallow, to reduce the cavity connecting to the pin.
This makes more power ( and is easy enough to tune ) than a non overlapping rear wall , with the optimum angle.

Thanks. Did you experience differences in jetting between those variants, e.g. the variant with the most short circuiting at the pin being the trickiest to jet?

[flyincat]

On the subject of Aux port connecting, and piston plugs. I'm curious about the mechanism of the plug. Does it work by volume reduction or by sealing? If it's a sealing mechanism, I have some questions about the shape. Frits shared a plug that, if I remember correct, had a spherical shape end. In the case of a spherical shape, with the same curvature radius as the piston skirt, the only good seal would be horizontally half way up the piston pin. This brings me to the next question. Would this type of plug work equally well in both pistons shown here? Note the dual pockets on the one piston would interfere with the horizontal seal halfway up the piston pin.

THere is one intermediate step available brefore having to use using pin plugs.
The exit angle shape of the Aux duct rear wall can be made shallow, to reduce the cavity connecting to the pin.
This makes more power ( and is easy enough to tune ) than a non overlapping rear wall , with the optimum angle.

[wobbly]

Kentastic made me some plugs in Torlon that matched the piston curvature , and had a small plastic ball in a machined slot
to prevent rotation.These had the clip captured and ran a slightly shortened pin.
These worked very well , except for a slight lack of axial clearance , that eventually smeared them up the bore.
But later I tested a simple flat faced plug and had trouble detecting any real difference in power.
All 3 versions I sketched will jet slightly differently, but once you have a weather/jet history its not an issue.
Only when running a big Aux overlap with deep pockets and no plugs do you run into short circuiting affecting the jetting response.
In my application there must have been insufficient lube access from the back of the pin boss ( no vertical holes into the boss either )
as I had trouble with the pin ends overheating.
This may in fact have been why the expensive Pankle , welded flat ended pins were favoured at Aprilia.

[husaberg]

I have never really understood why pressing in bungs works for big ends but is forbooten for gudgeon pins.
I are not having much like finding information that calculated the stess on each but i think Bell or Jennings covered it?

Anyone got any data?

closest i can find is this
http://www.nrb.com.tw/en/factory.html
Which shows a greater bearing load on the big end bearing?

plus the crankpin is also pressed in surely thats a load in itself as well

[Frits Overmars]

On the subject of Aux port connecting, and piston plugs. I'm curious about the mechanism of the plug. Does it work by volume reduction or by sealing? If it's a sealing mechanism, I have some questions about the shape. Frits shared a plug that, if I remember correct, had a spherical shape end. In the case of a spherical shape, with the same curvature radius as the piston skirt, the only good seal would be horizontally half way up the piston pin.

The plugs work by blocking the connection that would otherwise exist from the aux.exhaust ports via the gudgeon pin bore in the piston to the A-transfer ports.
A spherical plug is not the optimum solution from a blocking point of view, but it was the optimum that I could produce with the machinery at hand. Producing plugs with rotation-preventing protrusions would have required CNC tools. And the leakage past a spherical plug is limited. Below is the worst case, with a leak path 9 mm wide and 0,47 mm deep: a reduction of 88% compared to a plug-less situation.


Below: the latest, spherical-capped, hideously expensive but moderately sealing Pankl pistonpin as used in the works Aprilias and my re-usable (save the environment) Torlon plug, the chamfered pin bore in the piston not being a good idea in either case.

[41juergen]

I got my simple plugs laser welded which were CNC maschined with a radius matching the piston shape (incl. it's piston offset... ),
the welding costs only 20 €...