ESE's works engine tuner

[JdG]

On the insulation of the exhaust duct:

If the duct were to be perfectly insulated on the inside, there would be no heat transfer to or from the gas in the duct. The inside wall of the duct would immediately assume the same temperature as the gas inside the duct, whether the gas is hot or cold without any heat being transferred.

The interesting thing now is: Is the fresh mixture that has to be pushed back into the cylinder hotter or colder than the exhaust duct wall temperature when it enters this duct coming from inside the cylinder. The fresh mixture that scavenges the cylinder picks up heat on the way before it enters the exhaust duct. If this fresh mixture is actually cooled inside the (water cooled) duct, I assume insulating the exhaust duct would have a negative effect. If the cooling of the exhaust duct is necessary to prevent the fresh mixture from heating up, then insulating the exhaust duct would have a positive effect.

I'm very curious about the results of the tests.

Regards.

[Frits Overmars]

is their any kind of rule of thumb regarding the compression pressures above and below the piston on a two stroke engine which are deemed relevant for two stroke engine rpm?

Not so much a rule of thumb, but basic logic: you want as much fresh mixture as possible in the cylinder, so you want the pressure in the cylinder at exhaust closure to be as high as possible. But then you want the pressure rise above the piston as low as possible as long as the piston is rising, which means a low secondary compression ratio, followed by a cylinder pressure as high as possible, as soon as the piston is descending. That means: late ignition and fast burning.
In the Aprilia RSA the cylinder pressure at exhaust closure is about 2,6 bar. At TDC this pressure exceeds 80 bar as Wobbly mentioned, and 20° later it exceeds 120 bar. At exhaust opening it still exceeds 11 bar, which gives a nice bang for the exhaust pipe to work with.

Re the pressure under the piston: you want to inhale as much mixture as possible, so you want a low pressure in the crankcase during the inlet phase, followed by as much pressure rise as you can get when the transfer ports open. But the crankcase is a mediocre pump at best. Fortunately the exhaust pipe takes care of our wish list.
To answer your initial question: all of the above should be independent of engine rpm. Hence the variable ignition and exhaust timing tricks.

On the insulation of the exhaust duct: If the duct were to be perfectly insulated on the inside, there would be no heat transfer to or from the gas in the duct. The inside wall of the duct would immediately assume the same temperature as the gas inside the duct, whether the gas is hot or cold without any heat being transferred.

That would be true if the insulation layer had zero thermal mass. I haven't discovered such a stuff yet and I don't think it will happen in my lifetime.
Hence the practice of mirror-polishing the piston crown: It does not block heat, it merely reflects it, and there is zero time delay: as soon as the heat source is gone, there is no more heat. So cool mixture is not affected by previous hot gases. At least in theory .

[SwePatrick]

Testweekend writeup

My normal driver was sick so i called in an another friend, which sadly enough weights a lot more.
But, unimportant as i wanted a hard shakedown to test quality of engine and chassi.

We managed to run 39 runs with only one failure, the pipe cracked.
This was very good as i could concentrate on tuning.
Chassi worked really well, driver said it could easily handle twice the power.

Engine delivered same performance run after run, but after about 20 runs it started emptying the floatbowl, as i adjusted the trapspeed rised, and when all my trick up my sleeve was gone i used pipepressure to load fueltank with pressure.

Then trapspeed went up again, but weather had changed, different tents in the depot started to blow away.
It was hard wind straight against us when trying to get more topspeed.

The bike were sadly enough very high geared so it was hard to get it off the line.
Best 60ft was 1.89, i want 1.6x at least.
So if i gear it to get faster off the line i will lose trapspeed as is.
To get rid of this problem i have ordered a 2004 kx250 gearbox, it has taller gearing on 4th and 5th.
With that i can gear it faster off the line and still get high trapspeeds.

The clutch got huge amount of beating, and it just asked for more.
Carbon discs are the 'thing' it seems.

Only thing i adjusted was floaterlevel and the airbleed for lowspeed pilotjet.
Ohh,, one more thing..
I had to adjust the chain, brand new and it stretched some i guess, i´m running a small '428' chain

A small clip:

https://www.facebook.com/patrick.wet...5044821949475/

[breezy]

Peak combustion pressure exceeds 80 Bar, peak case pressure is under 0.5 Bar.

ok thanks .. would it be true to say that after combustion the speed of the descending piston through the first 180 * to btdc is faster than the next 180* back up to tdc due to no no real pressure being exerted from below the piston to increase its speed with only inertia of the crank in play?

[breezy]

"Re the pressure under the piston: you want to inhale as much mixture as possible, so you want a low pressure in the crankcase during the inlet phase, followed by as much pressure rise as you can get when the transfer ports open. But the crankcase is a mediocre pump at best. Fortunately the exhaust pipe takes care of our wish list.
To answer your initial question: all of the above should be independent of engine rpm. Hence the variable ignition and exhaust timing tricks"

oK Frits, thanks.Do you think if it were possible to isolate the traditional crank case from beneath the cylinder , which subsequently became the " crankcase area", with possibly a stepped type piston, with the smaller lower part of that stepped type piston passing through a sealed plate isolating the two areas generating a pressured area in the tradition crankcase area,. could that build up of pressure be used to propel the piston system back up from btdc faster than it would normally take in a traditional 2 stroke set up ...

[Frits Overmars]

What you are describing is a Ryger engine. It has a higher pressure under the piston and it would move the piston faster back up from BDC by a tiny amount if the piston wasn't much heavier than a conventional piston.
And what good would that do? That same higher pressure under the piston will also counteract the combustion pressure that brings the power. No free lunch there.

[wobbly]

At EPO the gas exiting the cylinder is entirely combustion by products and is hot as hell - we see 650* in the header.
At BDC we have an increasingly larger amount of raw fuel/air mixture being overscavenged directly from the case via the transfers.
This overscavenged mixture is cold and if done right it never exits into the header,there simply isnt time for it to be drawn down the pipe diffuser.
We see the result of bad short circuiting ( from port linking for example ) where the egt drops badly and no amount of rejetting will pull this up.
Thus the air/fuel mixture is surrounded by the duct wall, and any temp differential will try to attain equilibrium.
If the wall is hotter than the gas, it will heat the gas, made easyer by the fact that for some period of time the gas must be gradually slowing down,
then sitting still, then slowly accelerating again in the opposite direction ( as a pendulum does at each stroke extreme ).
Whatever the real dynamics of the system,the cooling water must have much less effect on the heat exchange process .
It aint over till the fat lady sings on the dyno,so the test will probably raise even more conjecture no matter what the result.
Unlike our still absent Ryger friend Luc, real dyno graphs will be published on here immediately.

[husaberg]

Unlike our still absent Ryger friend Luc, real dyno graphs will be published on here immediately.

But luc was going to post stuff, but only if you deleted your "Rude" comments
Oh wait you did, and yet he didn't post anything.

Only if Wobbly change his rude words very fast, otherwise no chance !

OK, so I have deleted all the " nasty " posts except for the " good " bit where I suggested that Luc maybe wasnt an incompetent idiot.
This now means I have a life, and I ( we ) would also be really,really friendly if the " hard proof " was posted here - a World Exclusive, as the media would say.
Your turn Luc.

.

i see Ryger are pushing the cleaner two stroke now rather than the most powerful ever..................

The Ryger Revo Clean 1 runs on normal petrol instead of a mixture of petrol with 2-stroke oil. Of course this already causes the first big advantage of having a much cleaner emission compared to the traditional 2-stroke engines.
Due to an ingenious design of the cylinder in combination with the piston and a bottom plate there is no fuel mixture in the crankcase but the fuel will only come underneath the piston where it is compressed and then being released on top of the piston after which ignition takes place.
With the Ryger Revo Clean 1 all the bearings run through the lubricant which is present in the crankcase and the piston is being lubricated via condensed lubrication. Also the gudgeon pin is being lubricated via condensed lubrication. This has resulted in a high degree of durability of the Ryger Revo Clean 1.
All the advantages of the Ryger Revo Clean 1 will help to get the best performance on a kart circuit. Due to the extreme output , the Ryger Revo Clean 1 is the strongest engine available in the 125CC category.
Because the fuel mixture is not pre-heated anymore in the crankcase the overall temperature of the Ryger Revo Clean 1 is much lower which has a very positive effect on the fuel consumption of the engine.

http://rygerengine.com/

[guyhockley]

Sorry TZ350. Bit off topic maybe...
It does concern an engine without poppet valves, though.
Brian Crighton, of rotary engined racers fame, lives near me, but I only found that out a few days ago.

http://www.crightonracing.com/index.htm

Unfortunately, the reason I found out is because his workshop was broken into and everything pertaining to his latest prototype was stolen. Local gossip is of the opinion it was a targeted theft.

https://www.facebook.com/CrightonRacing/

[tjbw]

But luc was going to post stuff, but only if you deleted your "Rude" comments
Oh wait you did, and yet he didn't post anything.


i see Ryger are pushing the cleaner two stroke now rather than the most powerful ever..................

Ryger said "Because the fuel mixture is not pre-heated anymore in the crankcase the overall temperature of the Ryger Revo Clean 1 is much lower which has a very positive effect on the fuel consumption of the engine."

I believe the Ryger fuel mixture receives more compression under the piston, than the VM engine on which it is based, so just before the transfer ports open, the Ryger mixture would heated more than in the VM engine.

The volume compressed under the Ryger piston, is less than on the VM engine, and that could result in reduced fuel consumption, reduced performance and reduced overall temperature.

Now, where did I leave my flameproof overalls

[seattle smitty]

Reading Wobbly's comments above on EGT readings prompts me to ask if anyone knows of a good discussion of how to obtain good reference numbers such as EGT, CHT, A/F ratio, water-temp, etc.. Most of the info I've seen comes from the sellers of these devices, or from four-stroke automotive drag racing sites.

I do get that given all the variables even in just the racing 2-stroke engines (on various fuels) covered here, it might be impossible to offer a one-dimension-fits-all statement on something like sensor placement (such as the "right" distance to place an EGT probe or A/F probe from the piston). I get that one probably shouldn't try to jet or time his engine using a reading from any single guage, that presumably the only way for any of these instruments, separately or together, to tell you anything very useful is once you have recorded their readings while having tuned your specific engine on the dyno and the track. But maybe the savvy guys here can offer some general suggestions on setting up instrumentation so it can eventually mean something . . . or refer me to such a discussion (again, specific to OUR particular engine types).

TeeZee, this thread makes for the best reading on the internet; thanks, bud!!!

[breezy]

What you are describing is a Ryger engine. It has a higher pressure under the piston and it would move the piston faster back up from BDC by a tiny amount if the piston wasn't much heavier than a conventional piston.
And what good would that do? That same higher pressure under the piston will also counteract the combustion pressure that brings the power. No free lunch there.

ok Frits thanks for reply. im sure you may have read this at some point which is an extract from a document,

" the pressure ( in the crankcase) may be either controlled manually or automatically. A higher pressure results in higher rotational speed and increased oil thickness or viscosity"

rightly or probably wrongly, i have thought that the "higher rotational speed", refers to the crank rpm. which is what im trying to understand.

[wobbly]

The position of an egt probe is relatively simple - 3X bore from the piston face is a good rule of thumb.
The raw numbers are a bit harder to nail down.
On track, the rule is to watch the egt and cht rising in unison,if the egt rises then drops whilst the cht continues to rise you are into deto.
But even easyer is to start rich and drop one jet at a time, and you will quickly discover that the temp will drop a set amount per jet size.
As soon as the egt delta temp drops from say 50*F to 20* with one jet leaner you are seeing the beginning of deto - go back one size.

One small element will change the egt's response in overev, if you have been clever and flat line the advance when approaching the mechanical rpm limit, the egt will
also flatline ( NOT DROP ).
This helps to keep using fuel to make power, not using fuel to control the continually rising egt due to ignition retard putting more and more heat into the pipe.
I use the max egt as seen with max power on the dyno ( at a specific RAD ) to construct a jetting chart,where for every weather data point I hit a specific best power egt number.
This egt ,over a fairly narrow sample range of jetting, will translate into a straight line relating RAD to jet size.

The last real trick to nailing best power jetting is to " read " the bottom face of the ring.
At peak power you will get tiny localized points of detonation of the gas trapped under the ring.
This "power deto " isnt enough to eat a piston crown, but indicates you are right on the limit - just safe enough for a 25 lap final.

[husaberg]

Sorry TZ350. Bit off topic maybe...
It does concern an engine without poppet valves, though.
Brian Crighton, of rotary engined racers fame, lives near me, but I only found that out a few days ago.

http://www.crightonracing.com/index.htm

Unfortunately, the reason I found out is because his workshop was broken into and everything pertaining to his latest prototype was stolen. Local gossip is of the opinion it was a targeted theft.

https://www.facebook.com/CrightonRacing/

I thought he moved to Aussie?
maybe it was to warm and sunny for him?
http://www.jpsnorton.com/race-bikes/roton/

[F5 Dave]

Oh good grief. I'd never think of looking at the bottom of a ring for jetting spec. Guess I'm well too lazy on top of tu stoopid.