Think of it this way?....
If you were the heart patient, whose advice would you trust: the Pacemaker Manufacturer OR the Surgeon that installs and calibrates it?

 

Think of it this way. What makes the most sense? How can a header, on a computerized car, "pull fuel"? Answer is, it cant.
I'll give everyone a buzz word, or term; ADAPTIVE STRATEGY. Thats what all CLOSED LOOP fuel systems are based on.
You make a mechanical change,the PCM adapts. It aint magic. Its simple strategies that were developed by the control system engineers to ensure that their systems would be able to correct themselves for different conditions, including someone tampering with them mechanically.
So, you improve the engines ability to move air, and the control system adapts. In closed loop it tweaks the amount of fuel it supplies, based on the 02 feedback. At cruise, in closed loop, its not a big change. But, stomp on it, and the computer goes to fixed table, which is nothing more than a multiplier, a fixed calculation, not based on feedback, to fuel the engine. At that point the engine is flowing more air than it did without the headers, but the fuel is still the same.
There are two ways to lean an engine. Take away fuel, or add more air to a FIXED amount of fuel.
Under these conditions, the computer cannot help but run the engine a little leanER. Remember, its still not LEAN, as that is an A/F ratio numerically ABOVE 14.7:1 (for a gasoline engine). It is simply leanER than it is from GM.
And to reiterate, this is not something I've seen once or twice. It something I've seen dozens of times. so much I can tell someone with these mods what the A/F will be before we run it on the dyno, and be within a couple TENTHS of a point, as long as the rest of the system is ok, primarily the maf not being contaminated, which skews the fueling terribly.

 

For the most part your posts are informative and certainly moving towards the continuing education of the CF community; however, you've made a few references to leanER as opposed to "lean", i.e. anything less than Stoich (14.7).

I've never, ever seen witnessed a competent tuner dial in WOT AFR's above 13.0; typically 12.5 to 12.8 is the magic number. You can (and will) damage engine components w/ sustained hard running at AFR's above 14.0. If this is not your position, please clarify. No accusations from my side, just want to make sure everyone here understands your opinions on proper tuning methodologies. Thanks in advance.

 

My reference to the difference, is to clarify. The reason being, lots of internet savy people continue to use the word lean to describe air fuel mixtures under 14.7 to 1.
This is simply incorrect. It is a common, and well known fact, that air fuel ratios much leanER than about 13 to 1 are dangerous. But, by definition, they are not LEAN. The basic difference being the amount of hydrocarbons left over after the burn.
That being said, the A/F ratio that best makes power differs from engine to engine. The safety zone also differs. I'll tune an engine thats normally aspirated, with forged pistons, leanER than I would a NA motor with the stock crappy hypereutectics.
An engine will continue to make power as you lean on it, until the point of incomplete combustion. The side effect is elevated combustion temperatures. Its the effect on the piston crowns that is the determining factor of whether the engine will live a long happy life, or a life like a wick on a stick of dynamite. Short, and hot.
And to further clarify, yes, I do keep all my tunes on the lower side of 13:1. But again, this by no means is lean. Lean by definition, in a gasoline engine, is anything numerically above stoich, or 14.7:1.
And incidentally, I believe I am one of the only tuners that doesnt only use a wideband, but a 5 gas analyzer. You see, part of my background is as an emissions specialist. So having a thorough understanding of the combustion process and being able to monitor things like hydrocarbons and NOX lets me be more accurate tuning idle on big cam cars (left over HCs and 02), and monitoring NOX to determine combustion temperatures at WOT. I am a stickler for accuracy.

 

I'm taking notes.

 

Here is a question for you guys.....What all this fluid sitting in my H-pipe?? I took it off today to finish painting it w/ high temp paint and there was black fluid in it?!?!? And it looks like there is fluid/fuel in the shape of little pellets sticking to the side of the pipe...
[IMG][/IMG]
[IMG][/IMG]

 

Don't know about the fluid, but the pellets look like weld spatter to me.
Ed

 

^^^ Def a fluid cause I wiped it away

 

You will get a lot of water as the product of combustion. The water mixes with the fresh carbon in the pipes and makes a dirty black liquid like coffee. As the exhaust heats up and vaporizes the water, the carbon will exit with the water vapor and deposit itself on the rear-end, or it will deposit and harden on the inner surface of the pipe.

Oh, I agree with all the comments on the learning ability of the PCM, and how it controls the AF ratio.
To clarify one point: it is my understanding that the computer will enrichen/lean out the AF as required at part throttle.
But then when going WOT, the computer will do two things:
a. Go to the preset WOT table and set the AF ratio.
b. Also look at the recent part-throttle adjustments, and
richen the WOT ratio IF THE PART-THROTTLE RATIO WAS BEING
ENRICHED.
C. However, it part throttle was being leaned, the computer will
NEVER lean the WOT, it will only take it to the factory preset AF
ratio table.
This, I suppose, is for safety, in case there was a faulty reason
the part-throttle was being leaned.

Thus, possible to get a richER AF at WOT, if the engine had been leaning at part throttle to reach stoi?

Is this correct?

DG

 

You are correct in your assumption that you do not want positive LTFT's (adding fuel) while tuning for WOT AFR. Ideally you want as close to zero as possible before WOT locks in the AFR. In the real world anywhere from -4 to 0 is good. The current tune I created locks in between -1 and 0.

 

When the vehicle in question goes to open loop at WOT, it doesnt lean the engine at all. It adds fuel via the PE which is a mutliplier.
With nothing more than a set of headers, on a stock engine, with everything else working the way it should, the LT trims arent affected drastically. A few points maybe.
But, at WOT, the headers allow it to FLOW MORE AIR, VERSUS A FIXED AMOUNT OF FUEL.
And for that matter, most if not all the cars I've seen, tuned, wont lock in the LT trims when they go into open loop at WOT. IF the LTs are only off a few points, as soon as you punch it both the LTs and the STs snap right back to 128.
And again, I have never, not one single time, seen a set of headers, on an otherwise stock engine, cause the AF mixture to be richER than it would have been from the factory.
Sorry if it seems I'm beating a dead horse.