Tune after headers, help me understand.
06-17-2015, 01:40 AM
#21
Burning Brakes
Since my last reply I added headers to my own car and updated the tune. As I said before the VE table needed updating for sure so I did that. I agree with the guy above that the MAF SHOULDN'T need to be remapped, but I checked mine and had more error than the last time I mapped it so I did make some adjustments. Can't say it was the headers that created the need to remap the MAF since the errors seem to vary by weather, gas, and by how I'm driving and what gear I'm in anyways. I also turned off the codes for the rear O2s. At this point I haven't changed anything else, but I think there are some adjustments I will be making to some of the idle tables as well as the several of the spark tables. I can also tell you that at least on my car, adding headers and clutch made my car run rougher (hesitation, dipping idle, etc.) than before and still isn't quite back to what it was, but I'll get there. I will be monitoring fuel trims as well and may be making some adjustments to the O2 sensor thresholds.
06-17-2015, 02:09 AM
#22
Burning Brakes
That's not correct. While there are a few ways to end up with the correct air/fuel ratio, not all methods are "correct".
The MAF cal is much more important than just measuring airflow.
Adding headers, you should always change the maf to do it by the book.
You can command a flat 12:5 AFR at wot and your MAF will reflect changes in airflow.
If you make your maf perfectly smooth like GM does it then you will be commanding all sorts of random PE numbers to make it work.
Not having a million dollar flow bench to calibrate mafs like GM does, in the field you must calibrate your maf on the motor.
When you do this your MAF absolutely reflect a change like headers.
Chuck CoW
The MAF cal is much more important than just measuring airflow.
Adding headers, you should always change the maf to do it by the book.
You can command a flat 12:5 AFR at wot and your MAF will reflect changes in airflow.
If you make your maf perfectly smooth like GM does it then you will be commanding all sorts of random PE numbers to make it work.
Not having a million dollar flow bench to calibrate mafs like GM does, in the field you must calibrate your maf on the motor.
When you do this your MAF absolutely reflect a change like headers.
Chuck CoW
Also, what you said is inconsistent with what I just experienced on my car. I just overlaid my new high frequency MAF curve with my old (before headers) and am pretty confident the headers didn't require the MAF to be changed. The main area I modified was around 6k hz, but that's because I have trouble tuning that area on the street because that's where I go into PE mode, which isn't the nicest transition so I get inconsistent errors. If I do "steady state" part throttle logging around 6k hz, as opposed to WOT, I get very different errors, so I kind of chase my tail in that region.... The only other change to the curve was at the very very top, but that's only because I was a little rich beforehand. I made no change to my PE table and still get a nice steady actual lambda at WOT, with like I said, essentially the same MAF curve.
I did put the following graph together which shows that the MAF frequency is higher for every RPM, meaning more air is coming in (more power!). I'm also going further up the MAF curve than before.
Not trying to argue by any means. Just like to learn.
Last edited by rio95; 06-17-2015 at 09:34 AM.
06-17-2015, 08:43 AM
#23
Race Director
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St. Jude Donor '15
That's not correct. While there are a few ways to end up with the correct air/fuel ratio, not all methods are "correct".
The MAF cal is much more important than just measuring airflow.
Adding headers, you should always change the maf to do it by the book.
You can command a flat 12:5 AFR at wot and your MAF will reflect changes in airflow.
If you make your maf perfectly smooth like GM does it then you will be commanding all sorts of random PE numbers to make it work.
Not having a million dollar flow bench to calibrate mafs like GM does, in the field you must calibrate your maf on the motor.
When you do this your MAF absolutely reflect a change like headers.
Chuck CoW
The MAF cal is much more important than just measuring airflow.
Adding headers, you should always change the maf to do it by the book.
You can command a flat 12:5 AFR at wot and your MAF will reflect changes in airflow.
If you make your maf perfectly smooth like GM does it then you will be commanding all sorts of random PE numbers to make it work.
Not having a million dollar flow bench to calibrate mafs like GM does, in the field you must calibrate your maf on the motor.
When you do this your MAF absolutely reflect a change like headers.
Chuck CoW
The problem is most people just change the MAF curve and don't know how to tweak injector data. That's fine, it works. But to say it's wrong is, well, wrong. When you get a spot in the MAF curve that is lean at one vacuum/RPM and the same spot is rich in different vacuum/RPM location.. what do you do? You can't fix it for both spots using only the MAF table.
Does it matter? Probably not. Fuel trims can soak up a ton of error and as long as you have PE fueling right it will work.
06-17-2015, 01:16 PM
#24
Former Vendor
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St. Jude Donor '07-'08-'09-'10-'12-'13-'14
I never do it like that.....
Like I said... many will disagree. If your injector data is right, the MAF curve will be smooth. Big IF. Even ID's isn't 100% perfect. That's why, at least IMO, so many people love SD mode. There are so many cells in the VE table you can pretty much make anything work (and work pretty well).
The problem is most people just change the MAF curve and don't know how to tweak injector data. That's fine, it works. But to say it's wrong is, well, wrong. When you get a spot in the MAF curve that is lean at one vacuum/RPM and the same spot is rich in different vacuum/RPM location.. what do you do? You can't fix it for both spots using only the MAF table.
Does it matter? Probably not. Fuel trims can soak up a ton of error and as long as you have PE fueling right it will work.
The problem is most people just change the MAF curve and don't know how to tweak injector data. That's fine, it works. But to say it's wrong is, well, wrong. When you get a spot in the MAF curve that is lean at one vacuum/RPM and the same spot is rich in different vacuum/RPM location.. what do you do? You can't fix it for both spots using only the MAF table.
Does it matter? Probably not. Fuel trims can soak up a ton of error and as long as you have PE fueling right it will work.
When you've done this a few thousand or (or dare I say a million...
) times, you should not have those problems.I'd have to see your tune, but something tells me you're missing a piece of the puzzle.
Send your file to me and I'll have a look at it.
Chuck CoW