I was wondering what the LTFTs and O2s numbers are on a completely stock car. I never scanned my car when it was stock.

Also, what's the a/f ratio that GM shoots for at PE/WOT?

 

With just a lid the Lterms were between 0 & -1.6 on my car. After Lid, exhaust, P&P&epoxy TB,FRA,etc. still about the same at cruising speed.

 

I just got to a-tap a buddies new 02 SS the other day.

LTerms were around +5 to +7 at cruising.

O2s were .88 to .89 at WOT (most the time)

Stock programming I believe shoots for an 11.9 a/f ratio.

 

That's interesting gwj, I bet every stock car is a little different.

NoGo, I'm surprised to hear 11.9/1, I thought GM was mostly concerned with fuel economy. Why not lean it out to about 13/1, have better fuel economy, and probably better performance too?

The reason I posted this thread is because I can't get LS1 Edit to connect at the moment, and my new pcm just has the stock fuel tables, and my car seems to be running better with the computer making adjustments on its own. I'm not able to connect EASE at the moment either, so I don't have any data to back this up, but when I'm up and running again with Edit and EASE I think I'm going to adjust my LTFTs with the Injector Flow Rate table instead of the fuel tables.

Thanks.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Predator:
<strong>That's interesting gwj, I bet every stock car is a little different.

NoGo, I'm surprised to hear 11.9/1, I thought GM was mostly concerned with fuel economy. Why not lean it out to about 13/1, have better fuel economy, and probably better performance too?

The reason I posted this thread is because I can't get LS1 Edit to connect at the moment, and my new pcm just has the stock fuel tables, and my car seems to be running better with the computer making adjustments on its own. I'm not able to connect EASE at the moment either, so I don't have any data to back this up, but when I'm up and running again with Edit and EASE I think I'm going to adjust my LTFTs with the Injector Flow Rate table instead of the fuel tables.

Thanks.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Emmissions is the last thing on GM's mind when the car goes WOT. Your EGR valve closes (if you have it), the car stops referencing the O2's, and basically ignores all emmissions monitoring equipment EXCEPT THE CATs. Which is why the a/f ratio is 11.9.

11.9 a/f ratio is a very safe setting, and does not sacrifice that much power (maybe 10 HP at the MOST). You cannot run the leaner a/f ratio's at WOT with the CATs on the car and expect them to last. This is also why your PCM has a cat overtemperature protection (COT) which acts as the last line of defense in protecting your CATs if you are beating on your car for extended periods of time.

Target A/F @ WOT = Part-throttle / PE Enrichment

For a stock car:
14.7 / 1.2403 = 11.85

Additionally, the EFI Live folks are reporting a commanded a/f ratio of 11.9 whenever they go WOT.

<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

Good points NoGo. I forgot about the cats.

So it seems that "cat preservation" rules over economy and performance, wide open. With the stock fuel tables, I have to be runnin' rich then.

It just seems perfect and correct though, that if your maf is stock, then your maf table should be stock as well. So it seems, correct me if I'm wrong, that with a stock maf you need to find another way to correct your LTFTs, other than with the maf table?

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Predator:
<strong>Good points NoGo. I forgot about the cats.

So it seems that "cat preservation" rules over economy and performance, wide open. With the stock fuel tables, I have to be runnin' rich then.

It just seems perfect and correct though, that if your maf is stock, then your maf table should be stock as well. So it seems, correct me if I'm wrong, that with a stock maf you need to find another way to correct your LTFTs, other than with the maf table?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I wouldn't say it is just "cat preservasion" but also ensuring that all production cars will operate with a safe a/f ratio at WOT. I have a-tapped a few stock cars, and typically, there is a span of about a 7% between all of the cars that I have autotapped in regards to reported air flow and LTerm corrections.
If GM programmed all production cars with a +/- 10% design deviation, the leanest cars would run 13.0 a/f at WOT (with the COT coming into play) and the richest would run ~10.7 a/f
I think it is just smart engineering not to produce 10,000 cars with programming that is on the ragged edge for performance.

In regards to correcting your MAF tables: Your MAF is not 100% accurate as it is. So, I do not see any problem in adjusting the MAF table a small percentage (ie ~5%). I have always said that if you are looking to make large changes to the fueling of the car, make your changes to the injector scaling tables (unless you are running a ported MAF). This way you won't run in to adverse problems concerning timing and engine load calculations.

And last but not least. A good majority of cars, especially the bolt-on only cars, should not need to make large changes to any of the tables. Typically, there is something wrong, like a ported MAF, slow O2, exhaust leak, vacuum leak, or something else contributing to the problem.

Good Luck,
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

Good info, and thanks, makes sense too.

"And last but not least. A good majority of cars, especially the bolt-on only cars, should not need to make large changes to any of the tables. Typically, there is something wrong, like a ported MAF, slow O2, exhaust leak, vacuum leak, or something else contributing to the problem."

I've recently come to that realization: I have a bolt-on car, but I've been attempting to tune it like it was heavily modded. Less is more on a bolt-on car. I did have a couple problems that explained why I was throwing lean codes with minor mods, but since fixing those problems, positive LTFTs well within the stock computer's ability to compensate (+or-25), is really the only area that needs to be tuned. Also the fact that my car seems to be running really good with stock settings seems to prove what you're saying.

I've learned a lot from all your posts. Again, thanks.

 

NoGo > Since my O2 readings at WOT are low 11:1, are you saying I should not get a MAFT and try to lean it out to 12.7 or so?

I don't understand why WOT A/F ratios are targeted at high 11s unless the car is ran at WOT for extended periods of time.

You mentioned that GM may have targeted high 11s because of a variance in actual results (say 10%), and that the leanest cars would run 13.0 - that seems to imply that 13.0 is an acceptable upper bound, otherwise they would have shot even lower. Am I wrong in thinking this?

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by soslo:
<strong>NoGo > Since my O2 readings at WOT are low 11:1, are you saying I should not get a MAFT and try to lean it out to 12.7 or so?

I don't understand why WOT A/F ratios are targeted at high 11s unless the car is ran at WOT for extended periods of time.

You mentioned that GM may have targeted high 11s because of a variance in actual results (say 10%), and that the leanest cars would run 13.0 - that seems to imply that 13.0 is an acceptable upper bound, otherwise they would have shot even lower. Am I wrong in thinking this?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You can not design and produce anything without some form of safety margin. Sensor accuracy deviations, casting deviations, manufacture defects, electronic performance are all items that are going to affect your cars performance, and that are going to be different on EVERY car. You can't engineer and manufacture an item and expect everything to be in tolerance. The real results will be closer to a bell curve, with the majority (not all) of your units close to your design specifications.
It is because of these deviations that no 2 stock cars put out exactly the same numbers. Sure, the majority are going to be close, but you are still going to end up with some cars that are dogs, and some cars that are ridiculously fast for factory specifications. They are often called "Factory Freaks" on this board. When I purchased my car in 2000, several cars put out 315 RWHP out of the box. Then there were other that put out 270 RWHP.

A 13:1 a/f ratio (peak power) is not going to damage your engine, and it is fine if you are running with this a/f ratio for a street car with cats that gets to see only occassional spirts at WOT. That is the whole point of aftermarket programming is to take your car to the ragged edge because GM production design will not.
If you plan on road racing it, and want your emmissions equipment to last for the next 50k though, then I would recommend shooting for a lower a/f ratio, or do like the rest of us and ****-can your emmissions equipment.

Good Luck,
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

Hey NoGo, how close is the target a/f ratio at wot to actual wot a/f ratios? I don't expect it to be perfect or for you to exactly know but I am just curious to if there is some correlation in order to get close to 12.8/1 without the use of a wide band.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by DailyAluminumBlock:
<strong>Hey NoGo, how close is the target a/f ratio at wot to actual wot a/f ratios? I don't expect it to be perfect or for you to exactly know but I am just curious to if there is some correlation in order to get close to 12.8/1 without the use of a wide band.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">On a car that flows air close to stock, the target a/f relationship with the PE tables is actually pretty accurate. The below equation has stood up fairly well for me on a near stock car.

WOT a/f = 14.7 / PE Value

I played with this equation quite a bit on my car before I started digging into the exhaust, and it was pretty damn close. Know though, that the above depends on accurate settings of your injectors, and MAF.

IMPORTANT:
As you start to free up more air flow though, this equation becomes more innaccurate and the car a/f will begin to deviate towards the lean side.
With a stock tune, my car will now dyno with ~13.7:1 a/f ratio.

I don't advise anybody to start programming their car towards the lean side unless you have some accurate form of feedback to determine whether or not you are too lean. When playing with the PE tables, and the MAF transfer function, it is very easy to take these cars into the red.

Good Luck,
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

I don't think you could go too far wrong (even if you didn't have a scanner) by taking a completely stock car, as an example, and using either a MAFT or LS1 Edit to lean out the PE table 5 or 6%. You'd definitely be moving in the right direction, and closer to an ideal performance a/f ratio.