ESE's works engine tuner

[jbiplane]

I use Stihl chainsaw cylinders on my motors. Recently I increased BMEP using increased stroke 43mm instead of 40, tuning exhaust reworked port map. Immediatelly got too hot cylinders head

Old combuction chamber on photo.

I want take out top of this cylinders and make new cylinders heads. What could be best shape of combustion chamber to use with flat top piston diameter 66mm? Max rpm are 9000, volume 147, compression ratio 12.5 (instead of stock 10.5). I want dont overheat engine working permanently more than one hour on 75% of throttle ~12hp at 7800 rpm. Engine is in air stream of propeller. Each gramm is count. Any advice?

Do I need place thermo insulation on combustion chamber walls?

[ken seeber]

WHY DO 2 STROKES BLOW SMOKE? (or do they just want lung cancer?)

After seeing skywriting planes yesterday during the Australia Day celebrations, it got me thinking. They do it by injecting oil into the hot exhaust = incomplete combustion. I’m sure we have all chucked on an oil soaked rag or bit of paper onto a fire. If it is really soaked we see smoke. Less soaked = less smoke. Years ago at Orbital we ran a generous flow of oil into the intake of a 2 stroke 4 cyl engine carb at high load. No smoke.

Can think of a couple of reasons for smoking, but based on the above, I’ll make the statement that a typical 2 stroke premix fuel (eg 25:1), if completely combusted, does not smoke, and, in the inverse, we get smoke.

Some possible reasons being:

1. One being the short circuiting of some of the charge, escaping out the exhaust and acting exactly like a skywriting plane. One test for this might be to run an engine on straight petrol, not withstanding that the petrol that has short circuited might smoke (a bit). Anyone want to give this a try, in the interests of science of course.
2. Oil, possibly with some of the petrol lighter fractions evaporating off (due to the high engine internal temps), working its way up the bore around the piston skirt and ring and passing into the exhaust passages.
3. An accumulation in the crankcase after draining down after stopping, either escaping into the exhaust directly or around the piston as above. Can be fully or partially eliminated by a draining circuit.
4. Similar to the above, but an accumulation of oil after full or partially closed throttle on an overrun situation passing thru engine.
5. An excess of oil being delivered to the engine, eg a separate pump controlled by a properly programmed ECU. My 300 EXC TPI is an excellent smoker at startup and low loads, either as a result of shit mapping or as per reason #3 above.
6. Others?

Gotta say that I have seen many (but not all) fast race bikes down the main straight and not blowing any smoke at all. Presumably this is because the plugging pulse is so strong that all the mixture that might pass out the cylinder into the exhaust passage is fully returned and fully combusted.

It'd be nice to be able to stop it. Thoughts?

[philou]

6 : shit oil. smoke whatever we do

Ipone Samuraï for example, smoke smoke smoke. not burning :malade:

[41juergen]

Ken, I would agree on your statements. I would think that smoke (I would claim independent if 2 stroke or 4 stroke, Gasoline or Diesel) in general results from an incomplete combustion. So either because not all HC (fuel only or any mixture with (2 stroke or engine) oil) are burned or washed through into the pipe outlet (more likely on a 2 stroke, but also a bit on a 4 stroke). So incomplete combustion happens during cold start (quenching and / choke used, so very rich Lambda) and later during the charging process when the plugging in a 2 stroke is not complete (but even with a 100% plugging, the combudtion itself will be incomplete, but not worse enough to create visible smoke)...

[MotleyCrue]

Take off the entire exhaust system and run the engine if it still smokes then incomplete combustion if it doesn't smoke then it was the oil laying around in the exhaust pipe that was smoking.

[husaberg]

WHY DO 2 STROKES BLOW SMOKE? (or do they just want lung cancer?)

After seeing skywriting planes yesterday during the Australia Day celebrations, it got me thinking. They do it by injecting oil into the hot exhaust = incomplete combustion. I’m sure we have all chucked on an oil soaked rag or bit of paper onto a fire. If it is really soaked we see smoke. Less soaked = less smoke. Years ago at Orbital we ran a generous flow of oil into the intake of a 2 stroke 4 cyl engine carb at high load. No smoke.

Can think of a couple of reasons for smoking, but based on the above, I’ll make the statement that a typical 2 stroke premix fuel (eg 25:1), if completely combusted, does not smoke, and, in the inverse, we get smoke.

Some possible reasons being:

1. One being the short circuiting of some of the charge, escaping out the exhaust and acting exactly like a skywriting plane. One test for this might be to run an engine on straight petrol, not withstanding that the petrol that has short circuited might smoke (a bit). Anyone want to give this a try, in the interests of science of course.
2. Oil, possibly with some of the petrol lighter fractions evaporating off (due to the high engine internal temps), working its way up the bore around the piston skirt and ring and passing into the exhaust passages.
3. An accumulation in the crankcase after draining down after stopping, either escaping into the exhaust directly or around the piston as above. Can be fully or partially eliminated by a draining circuit.
4. Similar to the above, but an accumulation of oil after full or partially closed throttle on an overrun situation passing thru engine.
5. An excess of oil being delivered to the engine, eg a separate pump controlled by a properly programmed ECU. My 300 EXC TPI is an excellent smoker at startup and low loads, either as a result of shit mapping or as per reason #3 above.
6. Others?

Gotta say that I have seen many (but not all) fast race bikes down the main straight and not blowing any smoke at all. Presumably this is because the plugging pulse is so strong that all the mixture that might pass out the cylinder into the exhaust passage is fully returned and fully combusted.

It'd be nice to be able to stop it. Thoughts?

They smoke when they have been idling or when they are cold, AFAIK Most pollution from 4t comes from when they are cold as well.
I assume thats where most of he smoke comes from with a 2t
AFAIK the DI eventrude ones have cleaner EX than the 4t doent they?
with the 2tA lot of emissions rather than just the smoke are related to the overlapping port timings i would think.
The injection just doesn't send fuel out the ex at low revs in the first place

[TZ350]

.
Recently with Flettners help I made a center drilled crankshaft for direct bigend oiling. It was feed by a small peristaltic pump and with a small motor speed controller I could control the oil flow.

If I cranked up the oiling. On the dyno after a full noise run with no fuel the engine would run just on the oil feed to the bigend.

[Peter1962]

.
Recently with Flettners help I made a center drilled crankshaft for direct bigend oiling. It was feed by a small peristaltic pump and with a small motor speed controller I could control the oil flow.

If I cranked up the oiling. On the dyno after a full noise run with no fuel the engine would run just on the oil feed to the bigend.

Did you modify the existing crankshaft, or was it a purpose built new one ? Do you combine this with oil injection in the throttle, like the TPI engine from ktm ?

[peewee]

Hello,

For a project I face a lack of space

is an asymmetry of transfers really harmful ?

Picture for example

i think those cyl have alot wrong. asymetric transfer passage. no inner and outer wall curvature. probly poor water cooling between cyl . exh passage looks very short. what engine do you have ?

[wobbly]

Peewee's cylinder is a HUGE over bored DM from CPI to fit on a Banshee bottom end.Its only real use is for open class drag racing where in Merican terms " bigger is better "
and the cubes overcome all the technical flaws.
My experience with these things is limited to the smaller Cheetah that can have a powervalve fitted.
Its intake is a CR250 that is offset outwards from center line 6mm per side.That reed is way too big for anything less than 120 Hp on petrol so I have fitted a smaller CR125 back on bore center and
picked up a minimum of 4 Hp in a 100Hp setup.
The DM has several good points about it , but would be better with a smaller bore to get somewhere near equal transfer duct areas , and some shape to the inner walls.
it also has replaceable Ex duct outlets , so making them longer and better shaped would be an easy CNC project.

[crbbt]

Just a question regarding tuning by the EGT and CHT.

If the motor isn't detonating at 660c exhaust temperature and above.
Would the next move be to increase the compression ratio or advance the timing?

[wobbly]

Depends entirely on if you have an adjustable ignition ECU.
With just the ability to wind in static advance , you will for sure pump up the midrange drive - and the added advance will drop the egt as well as reduce the overev ability.
If you then lean it down you MAY get back the overev , but that combination of extra advance and leaner jet , will also get you closer to deto - sooner.
Same with cranking up the com ratio , this also will pump up the mid , at the expense of egt and overev ability.
Again if you then lean it down , you MAY get back the rpm lost.
But with an adjustable ignition you can wind in the com , then back out some advance in the top end to bring back the egt and overev.
A win win.
If you are running a RS125 - get the April Systems switchable , curve changer ignition box , works a treat.

[ken seeber]

Vale: One unhappy IAME RL kart engine piston after an apparent coolant loss.

[Frits Overmars]

I knew that exhaust return pulses can be strong. I didn't know they could be that strong .

[TZ350]

Did you modify the existing crankshaft, or was it a purpose built new one ? Do you combine this with oil injection in the throttle, like the TPI engine from ktm ?

Drilled the original crankshaft and feed oil in from the drive end. Flettner made me a special big end pin with an oil passage in it.

20:1 fuel/oil ratio and a small peristaltic pump with variable output feeding the bigend.

The peristaltic pump can be manually speed controlled and also switched on/off as required by the digital ignition. I re-purposed the ignitions power jet control to do that.

With EFI, on overrun, I found I could turn the fuel off and pump excess oil to the bigend and the engine at small throttle openings would run on just the oil alone.

Another curiosity was that with the motor running, the large amount of air blown out through the oil feed line when it was disconnected. That is crankcase air blown back through the big end bearing and back along the oil passages. The amount of expelled air was quite surprising.

I intend continuing to use the peristaltic pump but will have it turn on for short discreet periods to just pump a small amount of oil directly to the big end. It wont have to be much to keep the big end healthy. The bulk of lubrication will be in the 20:1 Fuel/oil mix.