Strange tuning results, need ideas

[raddy]

Hi all

Recently I tuned mate´s Almera GT with SR20DE, radically tuned engine (high comp., very wide cams, exh. manifold, etc, 8500rpm rev. limit). I found that it provide best power (by monitoring TP in log) with pretty rich AFR of around 10:1 at full throttle up to rev. limit. Also, it holds higher TP up to rev. limiter. If I leaned AFR, it allways get lower TP and it falls down faster wit RPM. At 12:1 was different really noticeable, max TP was lowered from 115 to 95 and falls down much quicker with revs after 6500rpm. Also, car was noticeably slower by crew feeling. Its strange for me, that best results are obtained with so rich AFR, same for big difference at "more optimal" AFR... Any idea about this?

Another question is ignition timing calculation for this ECU. I was not able to get any higher timing that 32deg (consult reported) at last 3 columns of ign. table what ever was numerical value in cells set to. Any opinion about this?

thanks for your help
Radovan

[lyckaon]

It's possible that you have to much timing advance... or a fuel with octane too low for your compression ratio...

Did you try to remove some advance and lean out the mixture?

[Matt]

Not sure with the timing unless its an ECU internal limit which I dont know about. ECU part number for this? I can check it out on the bench

[PL]

Wow - those AFR's are really surprising. I've usually had best power by leaning them out. The last DE I did ran 13:1 and loved it!

I found that the DET's just love timing to make power, but don't respond as much to AFR changes (until you get below 11:1 and then they really drop off). But DE's seem to respond to being leaned out more - but don't respond so well to timing.

But with bigger cams and stuff maybe things are different. Seems weird though. ..

PL

[raddy]

Hi all
Thanks for inputs. I tested it before with less timing and with obvious AFR of around 12.5:1 (what I was originally aimed for), there was less power and noticeable TP decrease. ECU part number is N15 1N401, maximum reported timing was 32deg, whatever value I set in map. Maptracing using just same column from rpm midrange, so also interpolation should by not case here... Anyway, 32deg of timing looks just acceptable for mw, compared it with similar tuned SR20DEs, they using even more timing....There was no audible detonations, fuel is 100octane gasoline. Soon I will have dyno sheet to compare with previous tune...
Anyway, Matt, it will be nice to check if there is some kind of timing limit, thanks in advance....

[Matt]

No probs. ECU part number?

[raddy]

ECU part number is N15 1N401

[EngineWhisperer]

Wow - those AFR's are really surprising. I've usually had best power by leaning them out. The last DE I did ran 13:1 and loved it!

I found that the DET's just love timing to make power, but don't respond as much to AFR changes (until you get below 11:1 and then they really drop off). But DE's seem to respond to being leaned out more - but don't respond so well to timing.

But with bigger cams and stuff maybe things are different. Seems weird though. ..

PL

I wish I'd played more with that on my old SR20DE setup (6 years ago!)

I went from DE+T back to DE, and found that the engine didn't want any more timing than it did with the turbo on it.
From memory we left the mixtures alone (low 12s) so probably could have made some decent gains there.

[PL]

You may find that with the big cams your dynamic compression ended up being quite low. Big cams and extra compression go hand in hand. If your dynamic compression was down then it won't respond to timing.

Recently did similar with a mate's N14. Wouldn't respond to timing at all. In fact I couldn't even make it detonate - no matter how much timing I added! Had 260 degree Poncams in it but the inlet was retarded by a tooth. Fixed that (making inlet close 20 degrees earlier) and suddenly it's possible to make it detonate cos the dynamic compression has increased.

Interesting calculator to play with here:

http://www.rbracing-rsr.com/comprAdvHD.htm

PL