SladeX

Just wondering about the stock ls1 and its "11.7" PE enrichment stock value. Seems pretty rich when we're aiming for a 12.8 on aftermarket tunes.

Is this a blind safety setting, or do we make better power really rich? I recently dyno tuned my car and playing with the settings I stopped when I hit 12.9 (on tailpipe, have cats on car) but a commanded 12.5 (which reads right on the headers when we did some double checking). On reflection, I should have experimented with maybe a richer setting and seeing if I could squeeze more power out of it...

LSX Power Tuning

iTrader: (4)

Every combo is different. I havent had anything make the best power at 12.9 in a good while. If there is any ethanol in the gas (almost always now) they seem to make the best power a little richer. If you were commanding 12.5 and its 12.9 then you still have a little work to do on the fueling IMO.

SladeX

We figured out that out my tailpipe it was a 12.9 and on the header it was 12.5 so 0.4 difference. It's that I read after the cats when I did my wideband, so it should be more or less bang on to 12.5 if I did my runs with the wideband on the header. I also can still get gas around here with 91 octane and no ethanol. I'm going to book some dyno time in future and push a bit richer and see if I make any gains. Just for reference, what does everyone feel is today's "target AFR" for peak power?

dreww

iTrader: (1)

I shoot for 12.5 on my NA, bolton only z28

I shoot for 11.5 afr on my corvette with H/C/I/nitrous/Full bolt ons.

thunderstruck507

iTrader: (18)

My car seems to really like to be around 12.6-12.7 best. Doesn't get any faster leaner than that, but does slow down a little when I had tuned it in 2nd gear which was causing it to be 11.8-12.2 in 3rd.

LETZRIDE

iTrader: (6)

I think that is a safety...maybe I am wrong here, but the pcm can probably only compensate so much for DA right? So you have guys at sea level and guys that are 11,000 DA... what happens when the guys with 11,000 DA get on it?

I know DA made a difference on my 3.8 anyways...its how I went so damn lean on my 13.4 pass. I did tuning the night before when it was humid out, then went to the track (1.5 hours away) and the DA was below sea level...I went from a 13.0afr to a 13.9-14.0. Since my laptop was also dead, I couldn't compensate (hence the 13.4 run)...next day, back home she was beautiful again...

Like I said, I could totally be wrong, but that is my speculation as to why it is like that.

SladeX

The thing about commanded AFR with a MAF is that its commanded AFR is dependent on the MAF, so if you're MAF is dialed in correctly, the AFR commanded is based on the incoming air from the MAF alone. So as long as you have that correct, then it won't matter if you are at sea level or not.

This is why on different trips to the dyno I've been able to play with a very consistent AFR despite the days not having the same conditions. Once you bring it back to SAE on the results, you can see more or less the changes/improvements/drops.

redtan

iTrader: (5)

GM doesn't care about extracting the absolute most power out of your engine. What they care about is safety and longevity of the engine with thousands of tards out there most likely beating up on their cars. And when they have to warranty any type of damage done to the engine within a certain period, you better believe they will make it extra rich for safety purposes.

LETZRIDE

iTrader: (6)

from the way I understand things, the MAF reads air coming in. The lower the DA the more oxygen present in the air which requires more fuel. Regardless of the oxygen content the motor should still suck the same amount of air, meaning the same amount of air passing through the MAF for the reading.

Think of it as a rum and coke in a 250ml glass filled to the top, you can have a 25/75 mix and still have a full glass, or you could have a 50/50 mix and still have a full glass. The liquid in this case is the air, the content (rum) would be the amount of oxygen in the air.

I do believe that is one of the reasons why when it is cooler out, the car adds more fuel- because there is more oxygen present in the air (even though the actual air volume stays the same)

Again, maybe I am wrong, but that is how I have always understood it. Now granted, my tune was dumbed down to run strictly off the VE tables and no maf, and all my modifiers were zeroed out, so I had to make changes whenever the weather moved 8* or so.

danieloneil01

Oxygen % is the same at sea level or 10,000 ft.

sreve

iTrader: (3)

Yes but the pressure is not

The percentae of oxygen in the atmosphere does not change with altitude, so it is about 21% at 10 000 feet.
What does change is the pressure. This declines with altitude. At sea level the air pressure is about 101 kPa (kilopascals). Oxygen accounts for 21% of this so the oxygen pressure is 19.6 kPa. This means that there are less oxygen molecules in the same volume of air at higher altitudes. At 10000 feet the oxygen pressure drops to 7.2 kPa, which is roughly one third of the pressure at sea level.

sreve

iTrader: (3)

Sometimes. A 1ton truck hauling the queen mary PE delay can be 1minute
I assume to satisfiy the EPA.

redtan

iTrader: (5)

That may be the case down low, but at higher RPMs it's not nearly that long. I've seen several threads where a few tuners proved that wrong. Doubt many engines will last 1 minute at full throttle at 14.7 AFR.

danieloneil01

The google fu is strong with this one.

LETZRIDE

iTrader: (6)

But it is not the same per volume. Think outside of cars for a second and just look at athletes. They will train in areas way above sea level (like Denver) to train/condition their body on deprived oxygen conditions, and then come back and compete at sea level and benefit largely from the extra Oxygen volume in the air.

Whether or not the explanation above is exactly how it is or not I am not sure, that part is above my head, but I do know there is definetly less O2 in higher DA conditions. That's why they say cooler air is denser.

Now, our pcms have several modifiers for temp related conditions etc, but I don't know how it would determine a change in DA- but the extra fuel would cover it.

SladeX

As a chem eng, PV = nRT

It means that pressure and volume are proportional to the number of molecules and temperature. This relationship means that as you go closer to sea level, the density of the molecules increase per volume, hence if there is more molecules, there is potential for more pressure or volume given temperature stays the same.

The MAF reads incoming air based on the "molecules" hitting the hot elements on it. IF there is more molecules, then there is more chance the heat (energy) can be transferred to those molecules. The "ratio" of oxygen in the air to nitrogen and CO, CO2 etc is more or less stable around the planet so it is assumed there is x number of oxygen for y amount of air read through.

IF your DA goes up to 10000, less molecules essentially hitting the maf, if the DA goes down, more molecules hitting the maf.

So it matters A LOT that your maf is dialed in correctly. If you tune via PE alone, and the MAF is WRONG, on a given set of circumstances, DA, temp pressure etc, you will be right. as soon as you change one of those things, you will be wrong.

Your training analogy is a bit off. There is less AIR period when you move higher in the atmosphere. The ratio of O2 to N2 to x is consistent, there is simply LESS air altogether. IF your maf is dialed in correctly, then it will read like 10k hz at wot and if done right will still have the same AFR as if you are at sea level.

If things are right, then on a cold day, you hit 12k hz at wot because there is that many molecules cooling the maf. On a hot day, you may only hit 11.5khz. But because you have the maf dialed in correctly, you know thanks to PV = nRT that the number of molecules coming in has the right ratio oxygen and hence bang your AFR is CORRECT.

If your car goes lean in good cold air despite you "WOT" tuning via PE, that means your MAF calibration is incorrect. At part throttle, you have a sanity check for the MAF/MAP that says the tables say I have x amount of air coming in, the O2 sensor confirms or denies this. So the fuel trims add/remove fuel accordingly to correct the table's error. At WOT, you have no check, you are telling the car that at x frequency I have y air coming in. PE says enrich the table's values z percent to get commanded AFR. ECU has no clue what the end result is, but you do with a wideband.

jss812

Ooooo, a ChemE! I work with a bunch of ChemE's, about 5 of them are PhD's. These guys figure out how to make more stuff with what we have and in the process, usually create unique ways of breaking equipment. My job is to fix what they break.

Anyway, that's about the best explanation I've seen on how the system works.

So if I understand the procedure, the first thing that should happen is MAF is calibrated with WB. Once this is done, the rest is simply a matter of gathering data and generating tables, testing, correcting etc.

BTW, I often get a bunch of letters and lines drawn on my white board when ChemE's try to explain what they think is happening when equipment gets broken. I vaguely understand but can say that they have taught this old dog a lot over the years.