I've asked this elsewhere, might as well try here too

With the coming of the AEM ECU we now have FULL control over fueling and spark. I've managed to tune my fuel curve pretty well on my own and am now turning my attention to the spark curve. At this point I don't know a whole lot about how the stock Supra ECU setup timing. I've been toldthat it attempted to push 23degrees on boost and used the knock sensor to pull back from there. I've also been told that at cruise it would try to use as much as 50 degrees of timing. The "rule" here seems to indicate that more is better, is that really true? Shoudln't there be a point of diminishing returns where too much of the combustion process has begun and the piston is working too hard? Would that show up as knock?

Other than looking at the knock sensor for knock (and it's obvious when it occurs BTW) what shoudl be done to tune the spark curve? No way can I get 23 degrees of timing on boost with pump gas at higher RPMs but I might be able to do it at low boost - shoudl I be shooting for that? More than that if possible? Is 50 degrees of timing at cruise,with a reasonable A/F, going to get me decent MPG?

I'm edging on 40 now in some areas of my spark map and the car drives fine with A/F as lean as 18:1 light throttle. EGTs look fine. Just trying to get a feel for when I've got things optimized. Full power WOT tuning is actually MUCH easier to tune than part throttle around town stuff which is what so many people want to concentrate on. I'd appreciate guidance on what should work for part throttle timing and maybe some poiners on WOT timing.

Thanks!

P.S. On stocktwins now. I'mtold that moving to a single will change my spark curve a great deal

1995 Supra TT, BPU, FMIC, AEM ECU tuned by ME

I think this is a 'trick' question , and I believe you already have a substantial opinion on the subject. Having said that, lets give this a go from my perspective and let's see what others think about your queries as well.

First you probably have as much if not more understanding of how the AEM EMS operates as anyone on this board (that i am aware of), so you are beginning to understand the critical dependencies of tuning a EMS based modern EFI automobile car on boost. Secondly, I do not know of a single person who has cracked the factory Supra ECU, so the AEM is obviously taken standard EMS style technology and pushed it to a new level with a plug-n-play factory style connector based ECU. Since no one has cracked the ECU, then most factory data comes from tools like the Techtom (which I have) and other reading instruments. Timing 'jumps" all over the place on the Techtom in the ranges you speak about, which would be standard daily driving with a little goosing of the boost now and then, so coming up with a canned "what does the factory ecu do" response is difficult at best. WE can gain some ultra-stable don't move the gas pedal on flat land at a fixed ambient temperature timing data and 50 degrees is about what I have seen with the motor in a "vacuum" state. Under boost it is more stable, but you already know that.

Diminished returns on timing advanced usually comes when the mechanical components of the said vehicle can no longer function with the conditions that most often occur under heavy advance (assuming someone wants a reliable car), or air fuel ratios and drivability go 'whack'. If you are building a drag car and can afford a new motor every couple of runs you can go to methanol, crank the boost, double the key fuel map area's and advance the piss out of the timing.

You have a BPU car, so there is more leeway than with a big single or twin car in that you are not moving as much air and therefore can getaway with a bit more margin of error in tuning timing. I think the bottom line in tuning timing maps is to think conservatively whilst on boost, and to think more aggressively in daily driving, fuel economy optimization timing, while not sacrificing good driving characteristics. Beyond the tools you mentioned (monitoring knock, listening for detonation/pre-ignition, exhaust gas temperatures) and doing some tuning on a fixed dyno to simulate a load you are on your own.

You may want to try an in-cabin remote knock sensor and see how that correlates sensitivity wise to the factory sensor changes under load. Just another tool to dable with.

Whatever you learn, please share with the Supra community here because people here are keen to digest even a bit of meat in the midst of a lot of bones.

Good luck.

Mark Tozer
'94 Supra 915HP

quote:

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Shoudln't there be a point of diminishing returns where too much of the combustion process has begun and the piston is working too hard

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Thats why its called timing. You light it too soon, and lose power, even with out detonation. The crank is trying to come up and the combustion is so strong, it slows down the crank. The old chevy way of 'advance till it pings, back it off a degree or two' just isnt true.

1987 Toyota Supra

Heh, not a trick question I swear! Never put a scan tool on a stock Supra ECU either, my car didn't have one for long This is certainly a question I've asked all over the place and one I'm really trying to understand. No set opinions here.

I DID get a really interesting and sensical answer from "Glen" over on the AEM board. Trouble is that keeping track of all of the variables needed in order to see if you're making progress or not could be a real bitch and I'm NOT sure how much help we'll get from the software or how it could better help us

quote:

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If you are looking for maximum fuel economy you should (in theory)adjust the timing until the injector pulswidth is the minumum required to acheive the desired AFR. If you get misfiring/incomplete combustion it will show up as a lean reading on your WB and suggest that you add fuel.

The converse should work for power, if you are getting complete combustion and you have to add fuel to maintain the same AFR then you have made a change that is producing more power.

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Makes sense to me but unless you can hold the car on a load bearing dyno and adjust areas of load slowly I have no idea how the heck to zero in on this If I could figure out a way to get the ECU to help us tune this I'd ask AEM for it. AEM has already stated they won't dare try to "autotune" spark for fear of trashing motors.

Hrm, and a caveat - I've spent a bunch of time reading and learning about EFI and am playing with the AEM ECU daily HOWEVER I'm NO "tuner". I don't think anyone is likely to see me giving "tuning" advice. I'm moving slowly with my tuning and actually just had someone tell me they tried my map and that it was a mess for their car Every car is different but I'm looking forward to seeing just how different that car's map ended up being. At least it wasn't my latest map he was using so maybe the current one is better. Massive timing changes now and it DOES change A/F noticably so you have to be careful not to run lean after modifying things. I'll share my maps but with heavy caveats, I'm more comfortable sharing my DASHboards

Automapping at the end of the month should really help!

1995 Supra TT, BPU, FMIC, AEM ECU tuned by ME

I have been messing with Mani's Techtom on my BPU car and monitoring timing to see the differences between pump (91 octane) and race gas (110 leaded).

At cruise, depending on throttle position, I would see anywhere from high 30's all the way up to high 40's and maybe even 50 degrees of timing.

On high boost (1.2 bar) with pump gas, timing would retard to around 12-14 degrees, staying in the mid to high teens at low boost.

With race gas at high boost, timing stayed right around 20 degrees. Man I wish I could run race gas all the time...


-Ryan Hawkins
1993.5 Supra Twin Turbo
Auto BPU +
So. Cali.
12.02@116.5@17psi w/ 1.83 60' on Dunlop SP 9000's
My Mods
My Home Page
My Pictures

Thank you! That's a big help actually. I'm running around 13 at WOT now with a little knock when I hit the higher gears. That's in the heat too so I guess I'm not doing too badly. I'm running almost 34 in some parts of the midrange cruise - looks like I've got room to go up some I'm leaning it down to 16:1-17:1 though so I might not be able to take quite so much timing.

Thanks for giving me some clues, I appreciate it!

1995 Supra TT, BPU, FMIC, AEM ECU tuned by ME

No problem.


-Ryan Hawkins
1993.5 Supra Twin Turbo
Auto BPU +
So. Cali.
12.02@116.5@17psi w/ 1.83 60' on Dunlop SP 9000's
My Mods
My Home Page
My Pictures

Good luck with te tuning! I don't have the AEM yet but I must say that the manual is an excellent read for anyone that wants to understand how their car REALLY wprks. Anyways, I just had a quick, somewhat foolish, question for you BLKMGK. It has always been my understanding that the stoichiometric A/F ratio is a little less than 14.7:1. I was always told that running lean is pretty tough on an engines internals. Why then are you running such high A/F ratios? I guess I can't see the logic in this. Not trying to sound insulting or anything, I really wanna know. Thanks!

Wanted a Supra since I was fifteen. Slaved over a grill to save up for my dream. Then that movie came out and all the prices rose. Damn TFandTF, that movie f*ckin blows.

Under a heavy load that would cook the motor - yes. However this is under very light load cruising. 15.3:1 is actually supposed to be the most effecient A/F for mileage etc. I've recently been told. I do still run leaner than that - no misfire - but 16:1 is probably as lean as I'll go. So long as EGT isn't crazy I'm not sweating it. Over a loong cruise you could probably heat the exhaust valves a bit but on my car as soon as I give it gas off cruise and into boost it goes a bit richer and should be cooler.

Still playing with it right now. I'm comfortable with my timing for the moment but am working on getting A/F lean under WOT. 10:1 is a bit too rich (ahem).

1995 Supra TT, T-78, FMIC, AEM ECU tuned by ME

Ah, I see. Very cool man. Thanks!

Wanted a Supra since I was fifteen. Slaved over a grill to save up for my dream. Then that movie came out and all the prices rose. Damn TFandTF, that movie f*ckin blows.