Adding Headers and expected Fuel trims

[Beer99C5]

I thought I had a pretty good VE and tune going being all stock, My last log was the first with headers on it, and it looks like my trims are -8 Avg.

Naturally I gotta redo the VE Tune having added the headers, but that is what I should expect to see with adding headers? I believe I read headers lean out the tune because it makes the engine breath easier, so it would make sense that the PCM would want to add fuel to it. This being said my VE numbers should increase my next round of tuning more air = more fuel?

The other thing is the Racetronics pump has added about 2-3 PSI more pressure, that being said I would expect the car to be richer with the higher Fuel Pressure. So in fact my trims would likely be further out than -8?

Just doing a sanity check.

I plan on updating the IFR table to the new pressures and and then VE again. :Eyecrazy:

Am I on track or just all FUpped?

[redhardsupra]

i've usually seen about ~7-10% increase in midrange for headers. topend doesnt' change much at all which is kinda interesting. the most annoying part about tuning for headers is that it makes the knock prone peak torque area even more knock prone. so basically dont forget about your timing, as you WILL knock.

i've seen lots of people who put in headers, flow 10% more (which even on a untuned car with stock rich PE numbers will make it very lean), and then they wonder why the car didnt get any faster, as they knock and half their runs are ruined because of deminished timing.

[Redline Motorsports]

i've usually seen about ~7-10% increase in midrange for headers. topend doesnt' change much at all which is kinda interesting. the most annoying part about tuning for headers is that it makes the knock prone peak torque area even more knock prone. so basically dont forget about your timing, as you WILL knock.

i've seen lots of people who put in headers, flow 10% more (which even on a untuned car with stock rich PE numbers will make it very lean), and then they wonder why the car didnt get any faster, as they knock and half their runs are ruined because of deminished timing.

RHS,

I have been saying this for a while! We have installed tons of KOOKS headers on these cars and have seen the KR go up after headers which required some timing to get pulled. In addition I have also noticed that trims do go 6-12 % negative at low speed as well.

Howard

[Beer99C5]

Thanks guys, that makes me fell good :D Seems I was close on my Stock tune, and what I am seeing with my headers is to be expected. What PID do I log to see where I need to change my timing table? Naturely I have Spark and KR as PID's, what else do I need ?

Beer

[redhardsupra]

there is no way to figure out your timing on the street, or at least i haven't figured it out yet, and i've been trying for 2+ yrs now.

steady state dyno, partial throttle at arbitrary RPM's, and regulate AFR and spark (TOGETHER--they affect each other!) until you get the most hp. i've tried it using more empirical methods like time to traverse speed intervals measuring using both tuning software and gtech competition, but the small changes that timing makes is usually smaller than the regular levels of 'noise' you get by doing it on the street, with potholes, invisible inclines, wind, etc, so you'll never chase down your tail. dyno eliminates all these things, and gives you repeatability and precision, that's why it's the only way to Get it Right(TM).

[tblu92]

I thought I had a pretty good VE and tune going being all stock, My last log was the first with headers on it, and it looks like my trims are -8 Avg.

Naturally I gotta redo the VE Tune having added the headers, but that is what I should expect to see with adding headers? I believe I read headers lean out the tune because it makes the engine breath easier, so it would make sense that the PCM would want to add fuel to it. This being said my VE numbers should increase my next round of tuning more air = more fuel?

The other thing is the Racetronics pump has added about 2-3 PSI more pressure, that being said I would expect the car to be richer with the higher Fuel Pressure. So in fact my trims would likely be further out than -8?

Just doing a sanity check.


I plan on updating the IFR table to the new pressures and and then VE again. :Eyecrazy:

Am I on track or just all FUpped?

It doesn't make sence to me either---But typically LT headers always richen up the fuel rather than lean it down.Don't know why--Mine were almost exactly as yours-- -8 to -10 % accross the board

[redhardsupra]

in closed loop PCM detects a lean condition so just dumps extra fuel. because it's making these decisions based off a narrowband, it does not know just how much fuel to add, so it opts for the safer option and dumps a lot. this is what you might be seeing--overreaction.

this is why we tune. if PCM was able to detect and properly adjust for airflow changes, no tuning would be needed. tuning is just making it run very close to perfect, so the computer doesn't overreact.

[SSpdDmon]

in closed loop PCM detects a lean condition so just dumps extra fuel. because it's making these decisions based off a narrowband, it does not know just how much fuel to add, so it opts for the safer option and dumps a lot. this is what you might be seeing--overreaction.

this is why we tune. if PCM was able to detect and properly adjust for airflow changes, no tuning would be needed. tuning is just making it run very close to perfect, so the computer doesn't overreact.
This kind of contradicts the whole message in this thread. Everyone seems to be talking about negative fuel trims down low....so, wouldn't that mean the PCM is detecting a rich condition and pulling fuel?

Personally, I think there are two issues at hand:
1) The NBO2's suck with certain headers because the heating element is not strong enough to maintain the right operating temperature for the sensor to get an accurate reading. Being further down stream in the exhaust, it's naturally relying on that heating element more than it had to in stock form.

2) There's the natrual improvement in exhaust flow, which should create a lean condition. That lean condition would be seen by the O2's with substantial exhaust flow (which helps eliminate the lack of heat issue). Ideally, the car should run leaner and require positive fuel trims. On a stock car, a cold air intake, long tubes and catback generally require 6%~8% more fuel for commanded to match actual. So, that's 6~8% more fuel to bring you back down to the high 11's that come commanded from the factory.

That's why, IMO, they run rich up top and pull fuel down low. I wonder what a WBO2 would say when hooked up to one of these cars while they're in closed loop???

[redhardsupra]

This kind of contradicts the whole message in this thread. Everyone seems to be talking about negative fuel trims down low....so, wouldn't that mean the PCM is detecting a rich condition and pulling fuel?

That's why, IMO, they run rich up top and pull fuel down low. I wonder what a WBO2 would say when hooked up to one of these cars while they're in closed loop???

heh, the point here is that relying on sensors introduces a new layer of problems. it used to be that if something stopped working, that meant the part broke. nowadays, everything might be just peachy, but a sensor fails and suddenly car goes crazy. (ever tried to drive with a broken MAP sensor? :) )

what i've seen a lot, and it's a direct result of forums, is the belief that wideband is the solution to all life's problems. it's not. it's just a replacement sensor with more resolution. it is still subject to all the problems other sensors have. it might break, it might be miscalibrated, it might be trying to work outside of it's operational range, etc...
people look at the wb readout and follow it like the word of god. and more often than not it leads them down the wrong path. if you're trying to tune idle on a big cam, wb will say lean, so you put more fuel in, and it gets worse. do not follow sensors blindly. if the wideband goes on, it does not give you the right to turn your brain off.

computer has no common sense. humans do. when a computer reads that fake lean, it will dump more fuel. if that method was always perfect, we'd never need a human to adjust anything. that's not the case. if you keep adjusting stuff and there's no change, you're probably not changing the right thing, or the change gets ignored 'downstream' of the decision process. if you make changes one way, and you get a result opposite to expected, you probably want to rethink the process and check your assumptions.

so i guess the point of this entirely too long post is that if we're still falling for stupid sensor readings, what do you expect the stupid computer to do when fed funky data? dont be a stupid computer, dont follow data without understanding the process and questioning the correctness of the data.

[joecar]

Hmmm.... this brings us back to: "how do I know if this wideband is producing correct output...?"

[Beer99C5]

I was :)
Now I am back too :nixweiss:

:bawl:

It enough to drive someone to :beer:

I am going to load the stock 2002 OS (I am a 99) put in injectors values for my 42's @ 60 PSI, and start over with the VE, then MAF tuning.

[RevGTO]

This kind of contradicts the whole message in this thread. Everyone seems to be talking about negative fuel trims down low....so, wouldn't that mean the PCM is detecting a rich condition and pulling fuel?I don't think this question was addressed in the subsequent posts. Am I missing something here? Beer's seeing negative trims, not the positive trims that would indicate fuel dumping because of the apparent lean condition caused by the headers.

[Redline Motorsports]

Not for nothing but we installed over 30 sets of KOOK's LT's last year alone and everyone produced negative fuel trims over stock on mild cars. Even my new Z did the same thing.

[RevGTO]

This certainly runs contrary to my expectations, at least. What do you think causes this? I suppose VE tuning is the only way to compensate for it.

[ringram]

It doesnt matter what the wideband says as long as on mr dyno you are getting peak torque.
You can figure out if thats 15:1, 12:1 or 13:1 who cares. Let the Dyno tell you what to do.

Bottom line you need to sanity check everything on a dyno. Ive been once and I wouldnt consider doing anything else now. I had huge gains over my 18month experiment in street tuning spark etc.

Get thee to a dyno!

[oztracktuning]

THe problem with dyno's is that the AFRs will be different on the street regardless of whether the wideband is accurate or not. My best race tune is far from my best dyno tune.

With the headers - i would be checking for leaks or other issues. It really should have leaned it out.Turn off your trims tune it in open loop. But really the trims shouldnt be effecting PE mode unless the rest of the fuelling is out.

[Redline Motorsports]

Very true and this is why we dyno tune and back it up a the drag strip. We took my new Z from the dyno which I set the AFR up at a value that provided a max dyno number and made two pass's before we richened it up and the car made three more pass's with 3 more MPH. A proper tune needs to allow for this condition.