ESE's works engine tuner

[wobbly]

In all the engines I have done the area at the flange face is approx equal to the main port effective area, or approx .75 of all 3 ports.
The header diameter is equal to the effective total of all three ports.

[2T Institute]

Wob the Stihl pulls a good 10,000(TL 680mm)under load cutting a 18in hardwood log, ex width is low 60% as the piston has large cut aways around the pin. I got the largest rad I could(about 2.5mm) with a 60mm bore and a integral head, working from the bottom and through the ex duct.

[dmcca]

Wob the Stihl pulls a good 10,000(TL 680mm)under load cutting a 18in hardwood log, ex width is low 60% as the piston has large cut aways around the pin. I got the largest rad I could(about 2.5mm) with a 60mm bore and a integral head, working from the bottom and through the ex duct.

Sounds interesting, any pics or vid of it in action?

[TZ350]

With the triple port cylinder which has a main exhaust port 72% wide and with the 24mm carb on the left we have managed a best of 29hp, we have done better 31hp with a single exhaust port 75% wide which had less STA so something else is holding it back.

Maybe the restrictive 24mm carb regulation is starting to bite and its time to look at the plenum again.



The regulation 24mm carb made 29hp, now it would be interesting to see if we can make more power with a bigger carb. Next week I hope to try the 30mm carb in the middle and if that makes more power then I will re visit the 24mm plenum idea.

The plenum idea is a way to get around the restriction of a 24mm carb. Basically the plenum is feed by the 24mm carb and the engine draws from the plenum through a 30mm inlet tract.

On WOT the 24mm carb can flow into the plenum full time while the motor only sucks from the plenum for half the time. So the 24mm carb could effectively pass twice the air to the engine than it normally would.



The 30mm plenum runner has a butterfly for varying the inlet runner area and inlet timing. It basically halves the runners diameter and effectively closes the inlet 10 deg earlier. EngMod2T simulations suggest that there may be some useful low-end torque to be had.

The butterfly valve is operated by a small model aeroplane servo. http://youtu.be/FeB9O6rtLXQ

A previous problem we had was fuel dropout and puddling affecting the fuel mixture. The plenum has been sculpted with Devcon putty so everything drains to a low point and a scavenge pump removes the waste fuel/oil.

When we first tried it, start up was easy. http://youtu.be/YxiEo8cgopg then a bit of a blits up the drive. http://youtu.be/p4ef-WUO1Qs When the team first posted this, someone pointed out that a first gear run up the drive didn't prove much, they were right, but it proved it ran. I guess they were focused on the negative and didn't have the wit to see the possibilities.

We also ran it around the track at Mt Welly and it went OK but track testing was stopped when we realized that more oil than fuel was dropping out which meant that lubrication was a bit doubtful. There are a few oiling ideas like re fitting the auto lube pump or drip feeding oil directly to the plenums runner.



Anyway if it doesn't work out the plenum chamber makes a handy catch tank for the carburetor.

[TZ350]

I don't know who the rider is but its a Suzuki GP125 running at the Greymouth Bucket races.

[Frits Overmars]

The idea is a way to get around the restriction of a 24mm carb. Basically the plenum is feed by the 24mm carb and the engine draws from the plenum through a 30mm inlet tract. On WOT the 24mm carb can flow into the plenum full time while the motor only sucks from the plenum for half the time. So the 24mm carb could effectivly pass twice the air to the engine than it normally would.

Indeed. Nevertheless, you should pay attention to the flow through that carb because plenum pressure will drop during the inlet phase and you want to keep that drop as small as possible.
From what I can see, the tract length between the carb and the plenum is quite large, and so is the inertia of the mixture column in it. Though the flow through it is more or less constant, which lessens the inertia's influence, shortening it won't hurt. It will also create more room for an air filter (or should I say vacuum cleaner bag?).

The 30mm plenum runner has a butterfly for varying the inlet runner area and inlet timing. It basically halves the runners diameter and effectivly closes the inlet 10 deg earlier. EngMod2T simulations suggest that there may be some useful low-end torque to be had.

Maybe, but the inflow at the butterfly body looks terrible. I would suggest losing the whole butterfly body and fitting a short, well-rounded bell mouth instead. The better shape and reduced column inertia will promote max.power and overrev. Moreover you may be able to close the inlet earlier which will give you back your low-end torque and simplify setting the carburation. And you will have one less servo system. You know my view on construction in general and on racing equipment in particular: every part that you can leave out, doesn't cost anything, doesn't weigh anything, and never breaks down.

By the way, a 30 mm carb may sound large to you folks, but over here we run 32 mm carbs on 50 cc engines, and they behave quite civilized with them (and make some power as well).

[TZ350]

Thanks for the tips, I have a shorter belmouth to try, changing the rotary valve is a bit of a bother as I have to take the clutch off to do it, it takes about an hour to swap a RV, I will try your suggestions but it will take a few sessions to try a few different RV's.

[Frits Overmars]

Thanks for the tips, I have a shorter belmouth to try, changing the rotary valve is a bit of a bother as I have to take the clutch off to do it, it takes about an hour to try a RV, I will try your suggestions but it will take a few sessions to try a few different RV's.

No rush. I have ongoing projects that started 30 years ago .

EDIT: Maybe I can give you some pointers.
Closing the valve at 75° aTDC will give reasonable power and a friendly engine. Exceeding 85° aTDC may make the engine bad-tempered.
Trying disks with 75°, 80° and 85° will get you in the ballpark. I wouldn't bother trying intermediate values.

[ief]

I was curious so I thought I'd sim the triple port and lost power as well (just added aux ports to the single port setup and made the main port 72% and gave it a bigger radius) Then I lowered the ports a couple degrees and presto, power was back but...

With the triple ports the peak seems to go up the rev range and I don't see that in your runs and I wonder why?

I know I'm just messing about since the data is a guesstimate but still.

Also I wonder, your saying something else must be holding you back but wouldn't it to be expected that if the single port made 30+ hp the triple should be able to do that as well? I just don't see how something could be holding it back all of a sudden? Or if it does it seems something is just wrong?

[TZ350]

I was curious so I thought I'd sim the triple port and lost power as well (just added aux ports to the single port setup and made the main port 72% and gave it a bigger radius) Then I lowered the ports a couple degrees and presto, power was back but...

With the triple ports the peak seems to go up the rev range and I don't see that in your runs and I wonder why?

Yes, its suspicious ...

The way the side ports have been cut into the cylinder may be not so good and they don't flow as well as they should, its possible the triple does not have the STA I imagin.

your saying something else must be holding you back but wouldn't it be expected that if the single port made 30+ hp the triple should be able to do that as well? I just don't see how something could be holding it back all of a sudden? Or if it does it seems something is just wrong?

Yes, looking at the EngMod STA figures I expected the triple to easily make the same or more than the single port.

Everything else about the engine is the same except the glue in the transfers, the way I have gone about that may be whats wrong, its what I suspect anyway.

[ief]

Well, had a couple of hours fun with it and here are the results:

Little intro, when i got the files from you first thing i did was to detune it to get some figures more in line with your dyno runs, then i fiddeled around with the exhaust to see what i could get. Bin a while and i didn't save all the stuff but the red line is what i got i think. (if i remember correctly it was with an adapted early rs exhaust)

To make a long story short, i found that, with the triple exh. lowering the exhaust made better power witch to me suggests you'r loosing to much of the powerstroke now. Tried some different exhausts (adjusted them step by step) and ended up on the green line, about 3 hp more and lower in revs...

Witch brings me to your previous statement, it could be very well that your right that something is holding you back to get more power at higher revs, in the sim i am able to produce more power but at lower revs.

ps. I didn't change anything other then the exhaust and exhaust port between the triple and single port, well, except for recalculating the head.

For what it's worth and all that, if you like I can sent you the files, perhaps you can distill anything out of it.

edit: afterthought, lets see what this exhaust does on the single ex port. Was all most afraid it was all due to the exhaust but it seems the triple ports did something, pffffffff

[jasonu]

every part that you can leave out, doesn't cost anything, doesn't weigh anything, and never breaks down.

That is the quote of the century!!!!!

[Frits Overmars]

That is the quote of the century!!!!!

The century is still young, but thanks anyway, Jasonu.

[TZ350]

... i found that, with the triple exh. lowering the exhaust made better power witch to me suggests you'r loosing to much of the powerstroke now. Tried some different exhausts (adjusted them step by step) and ended up on the green line, about 3 hp more and lower in revs...

Do you have some numbers for the exhaust port or screen shots from EngMod you can post.

[ief]

Sure, this is what i ended up with for now... i'm sure with some more time there is more there but had enough for today.