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Please help, I am totally confused. With a completely stock 2002 Z, will the addition of a cold air intake, WITHOUT tune, cause a lean or a rich condition? Will the condition (lean or rich) be the same throughout the entire power band? I put an MTI true ram air CAI on my Z and althought I don't see a SOTP increase below 50 MPH, I do see a difference above 50. Also, I am not throwing any codes. Thanks for clearing this up for me.
John
 

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Adding a cold air intake .. ANY cold air intake, should not throw codes or cause a lean condition. Lean conditions/codes happen when unmetered air "leaks" into the sysytem after the Mass Air Flow sensor - and before the T/B. The unmetered air can cause a lean condition, plus unmetered air is not filtered so it is important to get the system air-tight.

There will be, with most systems, a 10-12 RWHP increase - especially initially, as the stock PCM runs a little rich - and the extra metered air will/should lean the A/F out SLIGHTLY after install. Many (me included) believe that affect is short lived as the MAF "learns" from the increased airflow and changes the A/F back to the factory setting. At that point the cooler, denser air is what is increasing power, not the A/F ratio. The only way to maintain an improvement in the stock (read rich) factory AF ratio is through tuning.

There are also some systems that create a slightly positive pressure at the T/B at speed (Vararam for example) which has a positive affect on cylinder fill rates. This positive atmosphere (also called "Ram" air) is a subject of much debate, some of it even informative - use the search function if that discussion interests you ....

Just my .02....

Les




John Youngblood said:
Please help, I am totally confused. With a completely stock 2002 Z, will the addition of a cold air intake, WITHOUT tune, cause a lean or a rich condition? Will the condition (lean or rich) be the same throughout the entire power band? I put an MTI true ram air CAI on my Z and althought I don't see a SOTP increase below 50 MPH, I do see a difference above 50. Also, I am not throwing any codes. Thanks for clearing this up for me.
John
 

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Discussion Starter #3
Thanks Les, your explanation is very informative. Anybody else want to chime in? I can't get enough info.
 

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I put a Vortech cold air system on. The car didn't benefit at the track until I did a dyno tune. I've also done headers, themostat, etc. If your not going to tune it I would leave the stock intake system alone. The good after market cold air and header systems increase flow if done successfully. If they are too sucessful, your computer will enrich the mixture to keep from burning a valve. This will, in effect, make your car slower than stock and depress your fuel economy (I assume you don't care about the latter or we would be on the Honda Civic forum). This is why a good dyno tune, and I mean real life not guess work, is the best way to truly realize a gain from your modification. Good luck.
 

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In most cases you will not get a lean condition. The computer will make adjustments for the increase in air by adding more fuel but at the same time your LTFTs are going to go on the positive side. What this does is make your car run rich at WOT or openloop.
This is why it is important to get the LTFTs as close to 0 as possible in closed loop.
The LTFTs keep track of the fuel being used in closed loop and refer to them when you go in to open loop or WOT.
So as you will not be running lean because the PCM is dumping fuel to make up for the increased air, the computer will also dump fuel at WOT if you don't reduce your LTFTs.
When you go into open loop the PCM refers to the PE table for the AFR. You might have the PE table scaled for a AFR of 12.8 but if the LTFTs says add fuel it could drop as low as 10.

The PCM will always relearn the conditions and keep the car at it's preset stoich value in closed loop but the AFR in open loop is reached by the scaling of the PE table plus the fuel added from the recorded LTFTs.

To answer your question, you will be at 14.7 or so in closed loop and most likely rich when you step on it.
 

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Tom is dead right. Low restriction filters, ported MAFs or throttle bodies will do the same thing and you arguably end up worse-off in the long run if you don't make other adjustments.

[OVERSIPLIFIED EXPLANATION = ON]

The MAF doesn't know how much air is flowing through it, only how fast the air is flowing. GM "calibrated" the intake system when they designed the PCM program so that the PCM "knows" how much air is flowing through the MAF at a given rate of flow (at a given temperature and barometric pressure) for the stock intake system's design. The PCM roughly sets the mix based on this calculation. So if more air can flow through the intake than GM programmed the PCM to expect, the mix leans out and you get more power. But... when the car warms up and goes "closed loop", The PCM starts to use the O2 sensors to see how good an estimate it's getting from the MAF. If the mix is too lean or too rich, the Fuel Trims are adjusted up or down. These adjusted values get added to the Injector timing, either increasing or decreasing how much fuel is delivered vs. what the PCM's base program was designed to deliver. The Trims adjust until the O2 sensor's output returns to the target AFR.

So you can't actually "lean out" the mix by reducing intake restrictions. The system corrects for the error this introduces and drives the system back to its target AFR. It takes a while for the Trims to adjust so you will see some initial benefit, but it will mostly go away over time.

But as Tom said, at WOT the PCM uses the MAF plus LTFT settings open-loop. If you've done something that's added more air, once the PCM has adjusted for it and the LTFTs have gone up, at WOT the engine might actually run richer than it was running before and you *lose* power.

That being said, you are reducing the pumping losses by reducing the restrictions along the intake plenum. This effectively pulls more air in each cylinder on each intake stroke. The PCM "knows" (or more correctly "has adjusted") for that extra air by adding extra fuel, but it's still extra air and fuel and that does make more power. But it's not a very big difference, the gains are minimal.

[OVERSIPLIFIED EXPLANATION = OFF]

The LS6 does like a fairly rich mix, though. It will safely make more power if leaned out a bit. There are MAFs that are recalibrated to compensate for more airflow, but this is a sub-optimal way to correct for a lower intake restriction. The right way is to get some tuning software and tune the car for its specific characteristics.
 

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The PCM's job is not to adjust to have a "perfect" tune or AFR, it's main job is to comply to EPA and function within a operating "window" range

That can be seen by just looking at LTFTs and you'd rarely see them close to a perfect zero
As long as the too lean or too rich DTCs do not trip the PCM is not going to make any special changes to bring short or long term fuel trims back to zero

MAF is a smog device as is the PCM and O2 sensors.

Cyberspace marketing hyped performance gains of "porting" MAF, TB and even larger airbridges or even the hype of FAST intake when the cylinder volume and the smallest diameter ( like runners) restricts flow other then how long a CAM grind is holding open the intake ports.

Most of those mods can cause a negative and cause the PCM to be lied to as to airmass and it's too late after the front O2 sensors reports the exhaust makeup after the fact.
Add headers that force the 02 sensors further downstream where exhaust is cooler and more lying as to true AFR is.
Ever notice a "claim" of performance gains of "porting" a throttle body which buffs out the input side but the butterfly is still the same size which means there is really no gain of air volume when the MAF is slanted to calculate "airmass"

The 0411 PCM used for C5s only have a 16 Mhz processor, look at the E38, E67 (C6) or new E92 for C7 and processors are much faster to do realtime changes the C5 is too slow to compute so any lying caused by mods are not addressed by PCM for values out of bounds to what the calibration is.
So in most cases 3rd party airfilter systems are not increasing flow at all and could even flow less then a clean stock filter.
Problems occur where 3rd party airpaths cause turbulence or worse induce unmetered airflow after the MAF.

Even the stock 2001-2004 MAF which is 85 mm ( 850 CFM) can handle 50 lb/min airmass which is more then enough to handle 500 HP even at density of sealevel.

In the end its very rare where the AFR is maintained at 14.7:1 for non WOT and even worse with today's E10 and E15 gas used in older designed C5s that have no way to see or adjust for how lean Ethanol causes.
Too lean should be judged as if and how much engine knock there is
and too rich as if engine runs sluggish or excess misfires.
 
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