Grumpy

As you may or may not know I've been chasing around building code for my GN for a few years now. I've literally spend weeks working on an ecm bench trying to get the code, to match the way I want the car to run. Unlike many, I'm terribly fussy about drivibility, and sustained high speed running.

The verdict is in, for what I think works, and is needed.

A fuel adder correction for time in Power Enrichment.
A Timing Reducer based on vehicle speed.
And a fuel adder based on vehicle speed.

Doing the above allows for PRECISE Control of EGTs! !!
And I do mean precise, I can maintain an EGT +-25dF during a 2 min run in boost. And it took thowing alot of fuel at it.... Now I can *flash* the EGTs almost the instant I get into boost, and not worry about them getting too high reguardless of time in PE, or speed.

11sORbust

I always thought it would be good to have fuel+timing adustments for each gear.....

kevm14

You could have a spark and fuel table for each VSS/RPM ratio (however many tranny speeds). But, it might be simpler to use an adder or subtracter (multiplier or divider?) based on going from a low gear to a high one. Like at low VSS/RPM ratios, use more spark and vice versa for high VSS/RPM ratios.

Or maybe more appropriately, an adder/subtracter or multiplier/divider that works based on RPM delta vs time (more advance for a higher engine acceleration rate). There could be a table of delta RPM vs spark advance multiplier. Something like this:

That's really what you'd be going for. Vehicle speed and gear doesn't matter. Or I'm all wet. Or this has been done before.

My '6965 $62 mask has a "launch mode" (tunercat's words) that adds spark advance based on IAT, delta map and a speed threshold, to improve off the line response. That's vaguely similar, but not really...

11sORbust

I know the factory code allows the a/f ratio to vary from each gear(because of load dynamics and no compensation). That is one thing I would make sure to fix if I could create my own source.

Grumpy

Yes they do. VSS is relative to areo loadings, and gear is about losing torque multiplication as you go up the gears. Your VSS PE compensations, can account for both areo, and gear loading changes.

You also need time. The longer in PE, the more the chamber temps start to slowly rise. This increase can drop the indicated AFR, due to the more complete combustion process, remember even a WB is an *Indicator*. Lots of log files that I've looked show O2s dropping as a run progresses, with even a slight increase in PWs.

I only mentioned these items, because they work.

kevm14

Ok so time and the RPM delta table I mentioned. I still don't think VSS, gear, torque converter, etc matters at all. The end result is, those things effect the RPM delta per time, so I was just saying base the table directly off that. Instead of saying "as we go faster, the engine gets more loaded by the aero loading, so the RPMs go up slower, maybe....and a higher gear means slower RPM change....maybe."

I just thought it would be simpler to go to the source - ask the engine what it's doing. It doesn't care what it is doing, only that it is producing power (for how long and how fast it is accelerating).

Aero is a load. Gears are a load. VSS is a load. The tranny, alternator, etc is a load. All these things effect how fast the engine can accelerate per time.

What if the car is on a dyno? There is no aero load. With my method, we'd still have "accurate" fueling because it's based on RPM delta per time. If the gear changed, the table would compensate. Headwind - compensation. Sudden electrical draw! Compensation. A/C - etc, etc. Even swapping in a different tranny, changing the rear, tire size, etc. - all of that would change a hard coded VSS vs fuel % increase table but would not effect an RPM delta per time fuel correction table.

RBob

iTrader: (1)

Many of the GM cars have a Launch Mode. Floor it from a stop and ignition advance is added. Gets the engine up onto the convertor faster and really gets them out of the hole. This timing is then (typically) gone by 10 - 15 MPH.

Reducing timing at higher vehicle speeds goes back to the days of 4 speeds and dual point distributors. Once in high gear the driver would flip a switch which would reduce the timing.

RBob.

kevm14

I understand this kind of thing is a problem for modified cars, or any car that has a serious traction problem.

Grumpy

So my actual results are moot, while your musing are valid, ugh, ok.

I've never seen a (engine) dyno win a race. Dynos (engine) are neat for R+D but often fall short of being, correct when the tune from a dyno is used in a car. Even chassis dynos often aren't the perfect tune for actual track use.

Grumpy

There's Launch mode, and then there's traction control.

Traction control would reduce timing to lower the HP to min tire spin.

Launch assist is taking advantage of the greater torque mulitiplication of first gear/ converter (and hence less load), to get the car moving.

JPrevost

Was this done with the c3 or p4? I'm assuming p4.
I can concure that engine dyno tunes don't work well in vehicles, especially when you're running alpha-n, ask me how I know.
Grumpy, couldn't the pulse width vs wideband afr be a transport time issue? 1st gear goes so quick, then 2nd, then 3rd is a slouch in comparison so the MAP and RPM are right but the wideband transport time might be shifted, or not, just trying to find out where the fuel is going since the only thing changing force wise from the motor is it's acceleration.

RednGold86Z

iTrader: (1)

Experts:
Is there code in GM's spark algorithm for calculating an almost accurate spark timing during high delta RPM (positive or negative)?

Like when shifting, the RPMs drop really fast. This means that if the RPM (time between ref pulses) from the previous two references is used for the next, then there will be an early spark for the next event, which basically is advance while RPMs drop (not good, could cause knock on shifts like many people see). The opposite is true for increasing RPM, where if the RPMs go up quickly, the timing will be late, thus retarded if not compensated. Could this explain what you're seeing?

I thought there was some code for that in the 749 hack that I read a while ago, but I can't access it from here, so I can't be sure.
Edit: Found it, there's something called DYNAMIC DWELL. Does this change calculated end of dwell (actual timing relative to ref)? Or does this just make a longer dwell that starts sooner?

kevm14

Not trying to be a dick here, but just help me understand. I also never said your results are moot. I was trying to find a way to more simply quantify your results. I.e. rather than saying it's a function of vehicle speed, gear, torque converter,
say that it's delta RPM/time, since that's what those things ultimately effect, as far as the engine is concerned.

Take a few seconds duration of a car accelerating. Call it a constant 1000rpm/second. What I'm asking is for you to explain how this engine could need different SA and fueling with differing vehicle speed, gear, torque converter, etc, but with the delta RPM unchanging. That is assuming it still ends up accelerating at 1000rpm/sec.

11sORbust

Been throught it with him...... VSS covers everything, like Grumpy said. Simple as that..

Z69

One problem with using delta rpm is that once you go steady state or close to it. Your table stops working because delta approaches zero or some low value.

For a drag app. the delta rpm might be a better or easier approach. I would imagine that in Bruce's case, it would be relatively easy to run 125-150kpa for a few minutes on the right road. With a rather low delta rpm.

JPrevost

It doesn't cover everything. Full tank of gas and 4 "heavy american" passengers with some gear says differently. Especially true with trucks where you could be towing something that just doesn't let the vehicle accelerate. A perfect example of this is my car with 2 of my friends and a full tank of gas, I've ALWAYS had to pull 2-3 degrees of timing out at WOT when going on a highway trip and trying to pass. Without them no problem, with them (and they're heavy dudes) it's another story. I wish I had room to datalog but like I said, they're BIG dudes.

3.8TransAM

Interesting Bruce,

But I'm scared to ask how much boost you were running for that long?

And was this on the c3 or p4?

later
Jeremy

RBob

iTrader: (1)

My money's on a C3.

RBob.

11sORbust

..... in your case, I would much rather add octane than cut timing. That's funny the big guys bog down your car. I just imagine two huge dudes stuffed in a f-body, passenger side sitting lower 2".

kevm14

Explain the first part, you lost me.

On the 2nd part - that's why I added to make a correction for time in PE or whatever. I think between time in PE and delta rpm/time, this fine tuning issue would largely be taken care of, without having to fuss over 3, 4, 5 or even 6 different tables for all the gears, worry about rear end ratios, traction, people in the car, etc, etc.

JPrevost

Yeah, it's pretty funny, but I love driving my car so I put up with it, sagging scrapping SFCs and all. They're not only heavy (340lbs and 270lbs) but they also don't pitch in for gas so 87 octane mixed with whatever was left in the tank... yes, 700lbs can make your car feel a tad on the slugish side. Almost as bad as going from my car to my friends 96 Imp.
RBob, my money is also on the c3 since I've noticed his more recent posts of daq has been lockers .

Grumpy

Grumpy

The ROMless C3.

I've tried it at varing levels for varing time periods.

I keep things to less the 18 PSI when in boost for more then 3-4 mins..


** Always bet WITH RBob**

Grumpy

You gotta have an EGT to really catch what all's going on.

While you can have the AFRs right, it apprears to me, that as the combustion chamber temps increase, so do the EGTs. So you have to add fuel as a means to cool the in chamber temps.. While in a strickly crag racing event, you're never at full load for a sustained period of time. So you in part just wind up adding fuel at the top end so it looks right. While that's fine, well, and good, for anything more then 13 secs atta time, the EGTs with increase.

These changes, really help in giving the engine what it wants......

While my other motor's heads have barrier coatings, and should help with this, I'm just wondering if the EGT issue is why GM and so many oems are going to AL heads.

JPrevost

You know I never did try and richen up the PE AFR, I wonder if that would have been a better idea... seems like it would.

From an inside source about AL heads; They're plenty durable and twice as easy to machine with tooling that rarely ever needs replacing so the tolerances are higher. I then asked if it had anything to do with cylinder temps but he didn't know since that wasn't his area. He then said that the resistance to warping/cracking, weight reduction, and expansion rate all were factors in aluminum's favor.