ESE's works engine tuner

[TZ350]

I have been thinking alot recently about how to keep heat from entering the GP125's cooling system and the exhaust tract was the most obvious problem area.

I couldnt help thinking there looks like insuficent cooling fin area on the scooter cylinders for sheding the wast heat from 25+hp even with forced air cooling from a fan. But looking at the scooter cylinder pictures I realised they have a much shorter exhaust port tract than the GP.

I would expect a shorter port to take up a lot less heat into the cylinder giving the cooling system a much easier time of it.

Now that I have seen this I remember my 1970 Suzuki TR250 had the exhaust port flanges milled right back into the cylinder shorting the exhaust tract considerably. I wonder if reducing the heat uptake through the exhaust port tract was the reason for doing it, those crafty old Suzuki tuners.

looking at the right hand cylinder in the middle picture you can see how short the exhaust tract is, and also the very clean (unmasked, is that the right term?) looking entries to the transfers.

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[F5 Dave]

You got kids too then F5?

Kids, they are great scavengers, mine send me loopy. and they know a thing or two about transfering wealth from my pocket.

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None outside the womb, but I have a reasonable memory from being a kid. My Dad didn't pass me on any race bike parts sadly, even if he was a dab hand with the right angle grinder. . . Mostly in Enamel though.

[F5 Dave]

Before you get carried away with transfer bottoms & all that palaver do drop a piston into the bore & ideally a case 1/2 with crank. No point looking at them in isolation, bit like porting 4 strokes without the valve etc.

[TZ350]

Before you get carried away with transfer bottoms & all that palaver do drop a piston into the bore & ideally a case 1/2 with crank. No point looking at them in isolation, bit like porting 4 strokes without the valve etc.

Good point, thanks. the transfer bottoms & all that palaver is something I am keen to get into but it will have to wait untill the motor comes apart again for maintenance.

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[SS90]

F5 Is quite right about putting the piston in the cylinder, then onto the case half.

There are phenonenal amounts of power to be made by using the right shapes.

This is also true of the scavenge patterns.

f5 also points out about the kickers (obviously you cannot incorporate kickers into your cylinder with out removing the liner, which is a shame)

But it goes to show that if you paid alot of attention to this area, huge gains can be made, and as you have such a small carb, it is even more important to get more efficiency.

Modern scavenge patterns improve efficiency dramatically. I, at first doubted such gains, but was proven wrong when I saw the gains it made on other engines, so I made the effort to change the patterns I was using.

The gains where amazing for such a small change.

In regards to heat Teezee, expansion chamber development over the last few years has enabled these engines to be making in excess of 30 P.S, and have no problems.

Of course, at that level of power, set up has now become critical, and of the Falc cylinders I have seen fail, all have seen severe errosion of the exhaust side piston crown, which suggests too much ignition retard.

[TZ350]

In regards to heat Teezee, expansion chamber development over the last few years has enabled these engines to be making in excess of 30 P.S, and have no problems.

I understand from the efficency of the Carnot Cycle that it does not matter what chamber, transfer layout or any other arrangement you have, when you make 30 P.S.....

Carnot Cycle:- http://hyperphysics.phy-astr.gsu.edu...mo/carnot.html

Using the simpler 1/3 rule of thumb, 1/3 for work, 1/3 down the exhaust and 1/3 waste heat.

30 P.S, means about 22,500 Watts of waste heat that the cooling system has to deal with.

The scooters don't look like they have all that much finning, do you use a special fan for the cooling?

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[speedpro]

. . . of the Falc cylinders I have seen fail, all have seen severe errosion of the exhaust side piston crown, which suggests too much ignition retard.

Every time I have seen piston crown erosion on the exhaust port side subsequent dyno runs have proven the timing to be a smidge advanced. With a few other tuning stuff ups I've managed to get piston crown erosion right in the middle. Not turning the water pump on was good for doing that as well.

Attached is a pretty old dyno chart. Ignore the red line that was a dodgy experiment. The line going to 13,500 was the old MB100 sidecar. That engine only had the original 2-petal reed block and a 28mm Keihin. The other line is my old piston port only TS100. 200deg timing on both intake and exhaust. I have no idea why it made such good power. Both peaked at 19.9rwhp.

As an experiment last Saturday at the track I held the throttle so that the carb was only part open, effectively creating about a 24mm venturi. The motor melted due to pumping losses, or something.

[Fooman]

30 P.S, means 22,500 Watts of waste heat ( using the 1/3 rule of thumb).

Do you use a special fan for cooling?

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Remember, not all the waste heat from the combustion is going into the cylinder head/barrel - quite a large amount goes out the exhaust, mainly in (superheated/saturated) H20 (lot of energy "stored" in steam). As you pointed out in your edit.

There I will stop, as I know sweet FA about dirty, disgusting 2-strokes - must learn more, having just inherited a GP100 with a watercooled head...

But, with respect to your oxidation problem with the copper lining, if you want to get a decent amount of copper in the chamber, try a thin coat of nickel (by thin, maybe 50 to 100 µm) or a nickel aluminide. The latter may be, um, difficult, to obtain over the counter as it were. That should be reasonably oxidation resistant. If it is thin, it won't affect heat transfer that much

Cheers,
FM


Ohhh, you edited it while I replied.

[Buckets4Me]

The motor melted due to pumping losses, or something.

bet you filled the crankcase up with petrol as well
wondered why you wernt there sunday

Nigel was fair flying

from back of the grid to 3rd before the first corner
then slowly picked Rick then Tim of to win every race

Zak made a desperat bit to pass Dave D on the last corner of the last race and hit him binning the Fxr Finished the race by pushing it over the line

[TZ350]

Remember, not all the waste heat from the combustion is going into the cylinder head/barrel - quite a large amount goes out the exhaust, mainly in (superheated/saturated) H20 (lot of energy "stored" in steam). As you pointed out in your edit.

There I will stop, as I know sweet FA about dirty, disgusting 2-strokes - must learn more, having just inherited a GP100 with a watercooled head...

The 1/3 rule of thumb says that if you are making 30PS (about 22,500 Watts) then you have:-

22,500 Watts of power 22,500 Watts of exhaust heat and 22,500 Watts of waste heat in the cooling system.

Only about 1/3 of the energy of combustion does any usefull work.

Ohhh, you edited it while I replied.

Sorry.

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[speedpro]

pg31 of the tuners pdf has interesting comments about the effects from the chamber on the transfer of mixture up the transfer ports and attributes the swift action equally to crankcase compression(7psi) and chamber created partial vacuum(-7psi). A crankcase compression ratio of 1.5:1 gives 7psi and also yields a volume that will be 1.5 times the cylinder swept volume. That volume may be a handy amount to have generally. If you were to remove a swept volume(only) of mixture from the cases the pressure would be back to atmospheric with the piston at BDC. With a larger volume you could extract the swept volume and still have a partially pressurised crankcase which wasn't resisting the continued flow of mixture up the transfers. Transfer flow would lose a bit at "first" due to lower crankcase pressure but would be compensated by what pressure there was dropping at a lower rate. You also have to consider when you think most of the transfer takes place and what is contributing to that flow at that time.

If the chamber is particularly effective it may be able to extract more mixture than is available. Reed valves are good here as they will admit more mixture to the cases if required. A late closing disc valve will do the same if the resonance is right. Of course it lets mixture escape back out the carb when it isn't. This is where my assertion that the crankcase is a storage container for the mixture comes from. I don't fully understand exactly what happens but from discussions it seems to be better to have the mixture required already in the cases. Something to do with inertia though I'd think that could be used to advantage if your lengths and volumes were right. Reed valve inertia plays a part as well and I think they will be closed and stay closed at about this time. Wobbly was adamant that my motor needed more crankcase volume to get the power I wanted(the most) at the revs the engine is now capable of. He's made a pretty good living doing this design work so I wasn't going to argue.

[TZ350]

Good post Speedpro.

Gordon Jennings book.

http://www.vintagesleds.com/library/...20Handbook.pdf

Page 106 talks about crankcase pumping.

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[TZ350]

“Experience is what you get when you don't get what you want.”


Thomas recomends these books on Two Stroke Tuning.
(Some of these are PDF's that can be down loaded, read them then get a copy of the book)

Graham Bell

http://www.kreidler.nl/artikelen/per...raham-bell.pdf

Gordon Jennings

http://www.vintagesleds.com/library/...20Handbook.pdf


http://toostroke.blogspot.com/2007/1...-handbook.html

Engine Formulas

http://members.bellatlantic.net/~vze...es/engine1.htm

Reading Plugs.

http://www.dragstuff.com/techarticle...ark-plugs.html

Rate of fuel burn and how it affects power output

http://www.factorypro.com/tech_tunin..._vs_power.html

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[SS90]

pg31 of the tuners pdf has interesting comments about the effects from the chamber on the transfer of mixture up the transfer ports and attributes the swift action equally to crankcase compression(7psi) and chamber created partial vacuum(-7psi). A crankcase compression ratio of 1.5:1 gives 7psi and also yields a volume that will be 1.5 times the cylinder swept volume. That volume may be a handy amount to have generally. If you were to remove a swept volume(only) of mixture from the cases the pressure would be back to atmospheric with the piston at BDC. With a larger volume you could extract the swept volume and still have a partially pressurised crankcase which wasn't resisting the continued flow of mixture up the transfers. Transfer flow would lose a bit at "first" due to lower crankcase pressure but would be compensated by what pressure there was dropping at a lower rate. You also have to consider when you think most of the transfer takes place and what is contributing to that flow at that time.

If the chamber is particularly effective it may be able to extract more mixture than is available. Reed valves are good here as they will admit more mixture to the cases if required. A late closing disc valve will do the same if the resonance is right. Of course it lets mixture escape back out the carb when it isn't. This is where my assertion that the crankcase is a storage container for the mixture comes from. I don't fully understand exactly what happens but from discussions it seems to be better to have the mixture required already in the cases. Something to do with inertia though I'd think that could be used to advantage if your lengths and volumes were right. Reed valve inertia plays a part as well and I think they will be closed and stay closed at about this time. Wobbly was adamant that my motor needed more crankcase volume to get the power I wanted(the most) at the revs the engine is now capable of. He's made a pretty good living doing this design work so I wasn't going to argue.

Nice to see you have been doing some reading.

As I pointed out in my earlier posts, particularly about "raising the primary compression", I was very cautious how I worded it, as, yes, normally, people cry "raise the primary compression", which indeed was true......50 years ago, as most two strokes where closer to 1.4 (or less), and therefore useless for anything like high speed operation.

Since the 70's, pretty much every two stroke engine comes standard with near enough to 1.5:1, and as such increasing it would only cause a peaky engine.

However..... Teezee, had lowered his (by modifications to make gains in other areas), and, as he measured it now to be something like 1.33:1, it's pretty clear it needs to be increased.

I did not advocate "just raise it".

And I quantified that with points I have just repeated here.

What is the ratio on your current engine?

I surmise while it may well be lower than 1.5:1 (but only just), and far more than TeeZees current 1.33:1

also remember, I have pointed out previously that the crankcase in a two stroke is also part of the intake manifold, and, as such, critical in tuning!

Every single engine is different, and while all the same rules apply, it's the application of those rules (depending on your criteria, like the fact that Teezee has to run a 24mm carb), that make tangible gains.

Current tuning "trends" are going towards lower ratios, yes, but those "lower" ratios are more like 1.48:1, I have seen nothing lower than 1.47:1

[bucketracer]

Does anyone know what a "scavenge pattern " is?

If anyone does, please post a) what a "scavenge pattern" is, and b) how they effect your engine.............

Home work from the Teacher, anyone done it yet?

Nice to see you have been doing some reading.

Once again Teacher, I dont know if you were borne stupid or if its a practised habit but your ability to offend is probably getting in the way of your message.


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