ESE's works engine tuner

[TZ350]

Just take a look at the detonation starting around Teezee's piston in the photo's from the last race.

Look closely, and you will see a "sand blasted" effect around the outer edge of the crown....

This is detonation.

Detonation starts at the outer edge of the crown.

However, this was caused (in my opinion), by the fact that you had the copper "liner" in the head, which, when it got hot, expanded, closed up the "squish area", and caused detonation (possibly was touching the piston at the top of the revs as well).

Looking at the pictures of the head after the race, the head shows the same signs of detonation.

The fact that the copper "liner" isn't pressed into the head is adding to the problem as well.

If a "cast in" cylinder liner ( like a your GP125 is) is better at displacing heat than a simple "pressed in liner", then the same logic applies in this situation.

I really believe, as has been stated much earlier on by a few people, finding an early "radial" head off the last of the air cooled motorcross bike (I.E, designed to cope with lower speeds, higher power), and adapting it too fit would be a wise move)

If it comes to it could make a big radial head from some large heat sinks I have.

We have made two versions of the copper head. Version one had a 1.5mm layer of copper plazma sprayed onto and into the combustion chamber of a modified GP125 head, which I would think would make a good thermal contact, and then teamed it up with a copper fin.

The thinking with this head was that the thick copper combustion chamber shell would be better at transmitting waste heat to the outside but the tarnishing of the copper became a problem, to be solved later.

The second one is basicaly an ordinary alloy head and like before its fitted with an oversized copper head gasket that extends into the combustion chamber to form the squish band and extends out the sides to form an extra cooling fin.

With the extra cooling the copper fin gives, the head runs at a measurably lower temperature. So I recon its a Keeper. The next part of the project is to reduce the heat uptake to the cooling system from the exhaust and add some air ducting.

This engine started with a 90 main jet and now runs a 112.5. Its funny, as we developed the engine we had to keep leaning the needle and richening the main jet.

F5 Dave suggested that because jetting up now, does not seem to richen it up, the needle could be controlling the fuel on full throttle and not the main jet.

We followed his suggestions, removed the main jet, ran the bike and it bogged from 1/2 throttle on, so this tells us that the needle and needle-jet combo are ok.

Looking at the piston wash pictures its clear like you say, the GP is running lean.

I have seen the sand blasted look of detonation before, mostly in other peoples TZ's. What looks like detonation in the picture is in fact the piston touching the squish band and polishing the combustion deposits on the edges of the piston. I ran my TZ this way and it worked OK, very well in fact, but I have to be mindfull that the MSV produced suits the GP.

From the piston wash pictures its clear that I could run the bike much, much richer and the wash pattern would tell me something about the transfer stream behaviour. Then following your sugestions and what I can find out from other sources make improvements.

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[xwhatsit]

Thinking of building a Dyno? Check out Geoff's homebrew dyno page:- http://geoffm.sitegoz.com/dyno/DIY_dyno.html

Just in case people don't know, that's the member geoffm from this site. He was having a dyno run the other weekend, bring some beer and have a go on the dyno... not many people turned up.

I think he's got it just south of Auckland.

Hit him up to have a go on it! I don't want to speak for others but he seemed rather keen to have people make use of it.

[TZ350]

Just in case people don't know, that's the member geoffm from this site. He was having a dyno run the other weekend, bring some beer and have a go on the dyno... not many people turned up.

I think he's got it just south of Auckland.

Hit him up to have a go on it! I don't want to speak for others but he seemed rather keen to have people make use of it.

Yes I will. Getting access to a dyno has been a bit of an issue.

.

[SS90]

If it comes to it could make a big radial head from some large heat sinks I have.

We have made two versions of the copper head. Version one had a 1.5mm layer of copper plazma sprayed onto and into the combustion chamber of a modified GP125 head and then teamed it up with a copper fin.

The thinking with this head was that the thick copper combustion chamber shell would be better at transmitting waste heat to the outside but the tarnishing of the copper has became a problem, to be solved later.

The second one is basicaly an ordinary alloy head with an oversized copper head gasket that extends into the combustion chamber to form the squish band and extends out the sides to form an extra cooling fin.

With the extra cooling the copper fin gives, the head runs at a measurably lower temperature. So I recon its a Keeper. The next part of the project is to reduce the heat uptake to the cooling system from the exhaust and add some air ducting.

This engine started with a 90 main jet and now runs a 112.5. F5 Dave suggested that because jetting up does not seem to richen it up the needle could be controlling the fuel on full throttle and not the main jet.

We followed his suggestions, removed the main jet, ran the bike and it bogged from 1/2 throttle on, so this tells us that the needle and needle-jet are ok.

Looking at the piston wash pictures its clear like you say, the GP is running lean.

I have seen the sand blasted look of detonation before, mostly in other peoples TZ's. What looks like detonation in the picture is in fact the piston touching the squish band and polishing the combustion deposits on the edges of the piston. I ran my TZ this way and it worked OK, very well in fact.

From the piston wash pictures its clear that I could run the bike much, much richer and the wash pattern would tell me something about the transfer stream behaviour. Then following your sugestions make improvements.

.

O.K, I fear some "Teacher" comments again...But.....


I think because of your transfer set up ("straight across the bore"), you cannot put to much stock in your (as you say) "piston wash"

If your piston is touching the combust chamber consistantly (as you say), then you are getting detonation.

When a piston touches the head (and it was in a somewhat cooler environment, that detonation is less likely to occur.....like a water liquid cooled engine), you don't get a rough surface, (like your picture), you get "shiny" "witness marks"

The surface on your piston crown is rough. That's detonation in my experience.

Detonation is not only caused by jetting, it's caused by primarily excessive heat in the combustion chamber. (which of course lean jetting will cause as well)

This can be for dozens of reasons (too much cylinder compression, too advanced ignition, too much dynamic retard, expansion chamber design, incorrect jetting), just to name a few....there are lots more!

With your copper head "combustion chamber insert", you are having problems.....the piston should NEVER touch the head, even more so in an air cooled engine. I know of examples of people running tiny squish clearances, and at the end of the race having small witness marks from the piston to head contact, but, they won the race. And these are water cooled engines.

That was the limit of the set up FOR THE ONE RACE

I forgot about your heatsink machined into a head idea, and I think it has merit!

Just to play devils advocate, I am no scientist, (and far from it), but does anyone know how good a heat sink is at expelling heat energy to the air? I am curious, as I appreciate they are good at drawing heat away from something, but what happens then?

But, the idea really has me interested. I would be VERY interested in the results.

[TZ350]

If your piston is touching the combust chamber consistantly (as you say), then you are getting detonation.

Why. Whats the mechanisim?

The surface on your piston crown is rough. That's detonation in my experience.

Your looking at a picture, when the guy on the ground says the squish area is polished its probably smart to accept it.

I forgot about your heatsink machined into a head idea, and I think it has merit!

Just to play devils advocate, I am no scientist, (and far from it), but does anyone know how good a heat sink is at expelling heat energy to the air? I am curious, as I appreciate they are good at drawing heat away from something, but what happens then?

But, the idea really has me interested. I would be VERY interested in the results.

I think that a large volume of alluminum might not "draw" the heat away from the combustion chamber nearly as well as a small volume of alluminum with fins close to the combustion chamber shell. When you think about the relative thermal gradiants you will see what I mean and why a copper combustion chamber shell looked promising.

.

[TZ350]

Detonation is not only caused by jetting, it's caused by primarily excessive heat in the combustion chamber. (which of course lean jetting will cause as well)

" (which of course lean jetting will cause as well)" not so! Leaning the jetting down allows the motor to make more of the power its capable of. The waste heat from this extra power overwhelms the cooling system. It’s the inability of the cooling system to keep up that leaves excessive heat in the combustion chamber causing detonation.

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[SS90]

Why. Whats the mechanisim?



Your looking at a picture, when the guy on the ground says the squish area is polished its probably smart to accept it.


.

Well, as you know, excessive heat in the combustion chamber is the primary cause of detonation. You have stated that the Piston is touching the head, now, applying just simple logic, now, as you have stated previously, there is "stretch" in the rod at high R.P.M (giving rise to the concept of "dynamic" cylinder compression ratio, now, I am putting forth the concept, that with the addition of this new "variable" of a Combustion chamber "liner" made of Copper (and copper expands quite dramatically with heat), your "dynamic cylinder compression ratio" is increasing with not only R.P.M, BUT ALSO TEMPERATURE!

Now, in the case of a water cooled performance two stroke, due to the fact that you have far more efficient cooling of the combustion chamber, if you run such a tight squish clearance (as you know, not to be confused with "cylinder to piston clearance"), say, maybe something like 0.6mm (just as a number), and you find at say 13,000 R.P.M, the piston just "kisses" the head, you may only find a small amount of detonation (or maybe none, due to the fact that the liquid cooling keeps temperatures low enough to surpress this), and, if perhaps you might finish the race, making power the whole time, and maybe, if you overrev it too much, the detonation may not be enough to stop your fun, it may well be the ring groove compresses from the impact and "jams" your ring.

Now, have the same scenario with an air cooled engine (and the increased combustion chamber temperature this brings with it), your outcome of this scenario looks a little more "Bleak"


Yea, I have to agree, I worded that incorrectly. sorry abouot that. Your "on the ground", I'm on the other side of the world. I'm not calling you a liar, but can you take a clear picture of the crown for me, I am really confident I can see detonation....Trust me, I have seen alot in my time! DOH!





Yea, I just don't know about the effect of the heat sink on a consistent temperature situation. (like prolonged operation at full throttle) Like I say, I'm REALLY keen to see some data....you never know...might try one for a scooter engine I am building for a friend...using your data as a model aye!

Try and get some heads (of different combustion volumes), as well as one of the heat sink concept, and do some "control situation" testing on a good dyno (and a good experienced operator), then I think you will have some very specific data that will help BIG TIME!

[SS90]

I have talked earlier about the "shapes" used in the case transfer areas..... this is along the right direction.....I use slightly different ones..... these particular ones are nothing new, and have been around for a while...... but I assure you there are good reasons why they are this shape...... It's not "just for volume"

[SS90]

With-out giving away too much, check out the transfer angles on this "Metra-Kit" teenage racing series cylinder...it's not the best picture (and from the wrong angle), but it's a good start!

(It's not the shape of the front transfer port that I am talking about (it's that way to allow for the auxillery exhaust port), I'm suggesting the angle they "spray into the cylinder"....

Note, they sure as duck guts aren't "straight across the bore"

[SS90]

" (which of course lean jetting will cause as well)" not so! Leaning the jetting down allows the motor to make more of the power its capable of. The waste heat from this extra power overwhelms the cooling system. It’s the inability of the cooling system to keep up that leaves excessive heat in the combustion chamber causing detonation.

.

That's what I said.... you just used more words to say the same thing!

I say lean jetting will cause the cylinder heat temperature to increase (and too lean even hotter)

You just elaborated as to why!

The result is the same.

[TZ350]

" (which of course lean jetting will cause as well)" not so! Leaning the jetting down allows the motor to make more of the power its capable of. The waste heat from this extra power overwhelms the cooling system. It’s the inability of the cooling system to keep up that leaves excessive heat in the combustion chamber causing detonation.

.

From SS90:- That's what I said.... you just used more words to say the same thing!

Maybe............

Its why I have been working on the cooling system.

Attention to efficiency not doubt helps but If you want more real power you have to have more cooling capability.

.

[SS90]

From SS90:- That's what I said.... you just used more words to say the same thing!

Its why I have been working on the cooling system. Good replys thanks 90.

.

Anyway,

Look forward to seeing the dyno curves..... I guess the whole point of what I have been writing is that there plenty of aircooled engines making high horsepower, and not suffering such big heat related power losses.

The solutions (in my experience) seem to be found in what I have posted.

I really am interested in seeing what power you have, as well as what your curve looks like.

As a side note, while I appreciate the fact that the peak horsepower number will vary from Dyno to Dyno, and pay little attention to that, in almost 10 years of operating various Dyno's around the place, I have personally never seen more that 17 P.S and 14 N.M (at the rear wheel) on an air cooled disc valve two stroke, running a 24mm carb.

I have probably done over 200 runs on that type of set up. (on various engines)

Number are just numbers though!

Lookig forward to it Teezeetreefiddy!

[F5 Dave]

TZ what do you mean by "Straight across the bore?" Do you mean viewed from the top?, or as I read it; angle of entry is horizontal across piston top? In which case where does the gas stream end up? Suzuki seemed to continue with the single transfer concept on the GP as they had on T series 70s bikes (or is my memory failing me?) long after they abandoned it in even TS engines.

[Fooman]

I am putting forth the concept, that with the addition of this new "variable" of a Combustion chamber "liner" made of Copper (and copper expands quite dramatically with heat), your "dynamic cylinder compression ratio" is increasing with not only R.P.M, BUT ALSO TEMPERATURE!

Why? Are you assuming that the copper insert expands into the combustion chamber? It won't. The insert is essentially a sheet with a hole in it. As the insert warms up, the hole becomes larger, unless it is sufficiently restrained by the shear force applied by the tension in the head bolts (in which case the insert will then have thermally induced stresses). Holes in things undergoing thermal expansion get bigger, not smaller.

There is a small mis-match in thermal expansion between aluminium-silicon casting alloys and copper alloys (copper doesn't expand as much, α = 21e-6 for Al-Si, 18e-6 for Cu), but the effect will be minor, especially given the mechanical restraint.

Cheers,
FM

[TZ350]

TZ what do you mean by "Straight across the bore?" Do you mean viewed from the top?, or as I read it; angle of entry is horizontal across piston top? In which case where does the gas stream end up? Suzuki seemed to continue with the single transfer concept on the GP as they had on T series 70s bikes (or is my memory failing me?) long after they abandoned it in even TS engines.

I think SS90 has misunderstood me. The main transfers are vertically flat (or very shallow) but angle back towards the rear of the cylinder. There are secondary transfers that look like add-ons and a rear boost port. When I run water through them the flow towards the rear wall. Will draw pictures and make measurements later.

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