ESE's works engine tuner

[SS90]

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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Ermmmm, I'm not quite sure of the relevence of the Carnot theorem here, (and how it relates to a Scnürle loop two stroke)

Especially when Carnot himself realised that in reality it is not possible to build a thermodynamically reversible engine.

Can you elaborate?

With the fan question, The shroud remains original, and is only cut to allow fitting over the large reed block housing (the reed block itself causes a cooling interference, but is of little consequence, especially if you drill a few holes on the back side to stop "hot air" being trapped at the small original outlet)

Don't forget that the 30 P.S plus engines are all Nicasil coated, not cast iron lined, as as such are around 30% better at dissipating heat than the lined ones.

The original fans supply plenty of air, and there are a few options for lighter fans (as the fans are part of the flywheel), which have less fan area, but cause no problems.

[SS90]

Home work from the Teacher, anyone done it yet?



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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Sorry, I can't resist......Can anyone spot the spelling mistake from this "pupil"........

"Borne stupid".....me???????

For the record, I have never claimed to be "teaching"...... I am constantly being asked to "prove things", and I try to do so in a simple easily read manner.... are you able to contribute anything to this thread other that antagonism.......

[bucketracer]

Sorry, I can't resist......Can anyone spot the spelling mistake from this "pupil"........

"Borne stupid".....me???????

For the record, I have never claimed to be "teaching"......

No, but you come across that way and it spoils what you have to say.

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[SS90]

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.

Ermmm, on the subject of exhaust side piston crown errosion, and too much retard.

As we all know, the primary reason for having a two stroke ignition that retards with R.P.M is to maximise for "peak pressure".

When you have very large exhaust ports, and then enlarge them more,(like all tuned cylinders are), you subject the exhaust side of the crown to increased heat.

If you have too much ignition advance, yes, you can erode the exhaust side away (particulary if you have a very wide exhaust port, by that I mean exhausts that use "bridges" allowing some phenominal exhaust port areas (exceeding 75% bore size).

On engines with-out exhaust bridges, as the port area is limited to somewhat less than 75%, the exhaust side of the piston crown is not subjected to so much "localised" heat, and normally, the hottest part seems to be the centre.

And normally, if you see a two stroke with a hole in the center of the piston, for whatever reason the overheating occured (be it jetting, or too much advance, or whatever), than engine is most likely not to have a bridged exhaust, and therefore smaller exhaust port size, and consequently less localised heating of the exhaust port side of the piston crown.

With alot of people experimenting with ignition timing, (especially on a dyno), it seems common pratice to advance their timing as much as possible, to get the best results.

Now, if you advance your timing "statically" (i.e-: move your stator plate), Since pretty much every "performance" two stroke, and most commuters (but not all), have a retard curve that functions solely on R.P.M, you also move the point that the ignition starts to "retard".

And therefore, the point where it "stops" retarding is further in the R.P.M range. And quite often, that new point can be too late.

Think of the factory setting of the advance curve only knows the original timing point as zero, if you move it ( for example, static timing minus 5 degrees), then the ignition retards that same amount later...... and finishes that same amount later.

Now that the timing is later than it's optimum, rather than firing causing nice combustion at "peak pressure" it causes a bigger "flame" to roar down the exhaust side of the crown, and into the exhaust port. (i.e AFTER the "peak pressure" moment has passed), when peak pressure is considered to be at 10deg? (I can't remember exactly!), think about how much of the exhaust port is exposed, if it happens later (15 deg, or what ever) much more of the exhaust port is exposed, exposing the exhaust side of the crown to greater localised heat.

Sure, too advanced timing can cause this type of erosion, but too retarded can cause the same effect.

This is one of the many reasons why fully adjustable ignition maps are so damn good!

You can set when and where (and how much) retard you have, rather than the basic R.P.M triggered system most every bike has. This basic system doesn't know how many R.P.M you have, it just knows 0.

[SS90]

No, but you come across that way and it spoils what you have to say.

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Well, lets leave all that in the past and move on......... Please.......

[bucketracer]

. are you able to contribute anything to this thread other that antagonism.......

Check the Teachers grammer.......

Yep I can....and I will also do you a favour and let you know when you are coming across as a dickhead......its what I am good at, after all we cant all be Teachers, if I antagonise you SS90 please understand its not my intention........


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[F5 Dave]

. . . . Reed valves are good here as they will admit more mixture to the cases if required. . . .

Or directly into the combustion chamber via the boost port, clear section experimental engines with high speed cameras have shown the reed closing from intake & then upper fingers of reed opening again to feed the chamber purely through pipe vacuum.

. . .. . 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.

Reed petal inertia will affect how quickly the reed acts to close, but the inertia of the incoming gas will keep the reed open longer slightly over stuffing the crankcase.

That all being said in the existing classes that power is important (125 & 250 GP) Disc valve is king. Reeds are still a big obstruction to the inlet, but life is about compromise.

[F5 Dave]

Hey I just read that old G Jennings Cycle mag article on piston/bore relationship & learn-ed sumfing. You don't have to smoke 2Baccy to enjoy the flavour.

You can chew it.

There, no issues with lung cancer to worry about (not that we believed that, - they said there was no scientific proof anyway).


1975 was another time another place huh?

[TZ350]

Ermmmm, I'm not quite sure of the relevence of the Carnot theorem here, (and how it relates to a Scnürle loop two stroke)

Especially when Carnot himself realised that in reality it is not possible to build a thermodynamically reversible engine.

Can you elaborate?

Scraped and edited from Wikipedia

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

For any engine there is a limiting obtainable efficiency it is called the Carnot cycle efficiency because it is the efficiency of an unattainable, ideal, heat engine cycle called the Carnot cycle. No heat engine, regardless of its construction, can exceed this efficiency.

In practice, because the operating cycles of real engines are nowhere near as efficient as the Carnot cycle, coupled with other irreversibilitys such as the combustion process itself and friction, real engines fall far short of the Carnot efficiency. Real automobile engines are only around 25% efficient.

Carnot Cycle:- http://en.wikipedia.org/wiki/Carnot_cycle

Thermal Efficiency:- http://en.wikipedia.org/wiki/Thermal_efficiency

Internal Combustion Engine:- http://en.wikipedia.org/wiki/Internal_combustion_engine

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

Referenced it to support the 1/3, 1/3, 1/3 rule of thumb I used to gestimate the waste heat to the cooling system.


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[TZ350]

With the fan question, The shroud remains original, and is only cut to allow fitting over the large reed block housing (the reed block itself causes a cooling interference, but is of little consequence, especially if you drill a few holes on the back side to stop "hot air" being trapped at the small original outlet)

The original fans supply plenty of air, and there are a few options for lighter fans (as the fans are part of the flywheel), which have less fan area, but cause no problems.

Waste heat to the cooling system is my current focus and I am interested in the practicalities of your cooling arrangements.

Do you think the shorter exhaust port tract on the Scooter reduces the heat takeup into the cooling system? The mean length of the GP125's exhaust tract is about 55mm long.

I would find it useful to know a Scooters head temperature and lower fin temperature measured near the exhaust after a good run, as a comparison. Would you measure it for me?

Because of your enthusiasm for crankcase compression ratios, induction resonance and unmasking the transfers I have become interested in looking at it again to see what more can be done with the GP.

But any practical work will have to wait for a little bit until I get to strip the motor for some gearbox maintenance that needs doing. Because of a damaged clutch nut thread I need to replace the main shaft.

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[TZ350]

Don't forget that the 30 P.S plus engines are all Nicasil coated, not cast iron lined, as as such are around 30% better at dissipating heat than the lined ones.

Isn't Nicasil more heat transfer cooling for the piston than engine cooling as such?

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[F5 Dave]

Um sort of the same thing in practice. A layer of plating will still create a thermal barrier, so it would be better to use untreated aluminum, (if it didn't wear of course) but the barrier is considerably less that a steel sleeve, so more heat is passed to the outside ally rather than retained in the sleeve & hence the rest of the engine.

A compromise you may think would be to make a ally sleeve & plate that, but while you have similar materials you still have a physical interface worse than the original cast over sleeve. It should still be better I imagine, but before you run down that path you would have to find the right ally, most you get in NZ aren't suitable for plating. Probably 4042 alloy, or maybe 6060 or 6261 which are suitable for anodising so should be ok for plating.

Oh dear, how can you close Pandora's box?

[TZ350]

The basic idea I'm sure everyone is aware of, it is in every 2 stroke book, probably even Roy Bacon's old duffer books. To get a visualization run some water through the bottom of the transfers & see where the flow is directed, - this of course is not a full dynamic model but is interesting & with later designs how this has evolved & how effective the kicks have become esp in the 2ndries. Where this flow ends up & how effective it is in containing charge by reducing kinetic energy & purifying what is left will all affect the result. Overboring or sleeving will put this to pot a bit wrt to transfers.

"kicks, esp in the 2ndries" I didn't know what F5 meant but found the answer in the pic below. I had seen them in barrels before but did not know that they were called kickers.

Scraped from MacDizzy's finding the sweet spot:- http://www.macdizzy.com/cylinder_map6.htm

The rear transfer port has both of its walls cut at 90°, but the rear wall has a different angle cut into it at the liner - a sort of kicker- to make the charge push forward. The direction of the front wall of this port would be directly in line with the opposing port (if I drew it) - so the released mixture will collide with each other. This helps to keep the fresh mixture in place and helps prevent it from exiting the exhaust port.

These port walls determine where the new mixture goes. In general terms - ports that are more directly opposite each other tend to make more peak power. Range comes from aiming the charge more rearward. The combination of these angles and the upward angles of the port roofs shows a wide range of possibilities within any engine.

The major components here are the cylinder ports size, shape and angles - both horizontal and vertical. The transfer ports of the engine have as much to do with the way the engine runs and its behavior as the exhaust pipe. It could be said that the transfer ports deliver the spread or range of power while the tuned pipe balances the delivery and availability of that power.

Read more here:- http://www.macdizzy.com/cylinder_map6.htm

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[Buckets4Me]

Oh dear, how can you close Pandora's box?

buy an FXR

[TZ350]

1975 was another time another place huh?

Been there done that!