WAHUSKER

iTrader: (4)

To set the playing field, I have never played with my MAF tables. I've set the VE & PE & IFR & yada yada yada. But never the MAF because I've always been able to get the car "close enough".

But now that I have a blower on the car, at roughly 5250 rpm the air flow reaches the max number entered in the MAF table cells. Looking at the tune, from 11kHz up the number is flat (439 g/sec). So the obvious first thing to do seems to be change those cells to extend my curve up so the MAF will read the increased air the motor is getting.

However, reading thru the sea of RedHardSupras & jimmyblues & Horists information, maybe that ISN'T the right thing to do. But it seems to be more or less OK reading the air & compensating up to that point. And the motor getting more air that it thinks it's getting at max power is surely a bad thing.

So is this a good place to start, and then calibrate the MAF from there?

jimmyblue

iTrader: (11)

If you have the Camaro style MAF the older tables don't
do it justice; they flatline it well short of the 512 g/sec,
12kHz limits. If your table goes out that far then I'd go
and populate it with the Holden MAF table and see how
that plays. Some OSs might not go past 11500 but have
to try and see if you suddenly get sane numbers up top.
That would give you maybe 17% more airflow range
before you start to lose fidelity.

RedHardSupra

iTrader: (1)

the problem with MAF and FI is that the max value in the PCM in the MAF table is 512 gram/second = 67.726 062 188 pound/minute, which can be easily outdone with any form of FI. so it is physically impossible (short of altering data types on the pcm, or using frequency dividers) to modify the system in such a way that the MAF would accept more airflow than the 67lb/min. That's the real reason why MAF and FI don't mix.
a basic STS system at 5psi will hit that much before 5000rpm.
So if you got a FI system, you either go SD or do some serious hardware hacks.

2002_Z28_Six_Speed

iTrader: (19)

Basically you are talking about doubling the word size of that variable through the PCM code then making it actually work.

WAHUSKER

iTrader: (4)

Holden MAF table? I'll go search. So it sounds like I can increase the table, but the limit is 512 g/sec (which is funny cuz that's about where I ened up with the make believe numbers I entered). BUT my blower, even tho it's just a P-1SC, will exceed that level well before my 6500 rpm redline.

So I guess I either need to go SD, or buy a bigger MAF? Not trying to irritate all you tuner junkies (since I need your help) but SD seems like it would be a major PITA trying to compensate for weather changes, or when I trailer down to Nevada to run a race, etc etc. So would something like an 85mm SLP MAF help me? After I rescale my tables?

2002_Z28_Six_Speed

iTrader: (19)

It would flow more but the 512 number comes from a limitation in the computer. 512 is the largest number in binary you can have without having to rewrite the code.

Maybe you could get away with having it maxed out. Leave the MAF plugged in on the street and don't run it at the track. It is going to suck to have to fine tune it at every event but I can't think of a way to help.

Does anyone know if a custom OS would fix this?
Aftermarket FMU to piggyback on the OEM computer?

WAHUSKER

iTrader: (4)

Ah, the 512 is the PCM limit, I missed that part. OK, NOW I understand. Sorry, I'm s..l..o..w

WAHUSKER

iTrader: (4)

Thought I'd post an update. I revised the MAF table so the curve continued up to 512 (OK so HPT maxes out at 511.99), tightened up the s/c belt, and gained ~20rwhp & 93 ft-lbs of tq. Granted this was also after a Racetronix pump install, and a 3.40 gear swap (from 4.11s), but I think the new table numbers make it better. I did that on the last run after I was having trouble pulling the a/f numbers in line....the PCM now understands.

muncie21

iTrader: (14)

Congratulations on getting it tuned in so quickly. I guess have a dyno handy probably speeds things up a bit.

WAHUSKER

iTrader: (4)

Now that I deleted my cats (one was 75% collapsed) my MAF is maxed out again. Although I gained another 15hp & 40lbs of tq!

So I picked up an 85mm SLP MAF from a friend.....but from what jimmy & others say in other posts, it won't help. Is that true? It's seems contrary to logic. How could it not flow AND read more air than my stock 78, especially with the tables tweaked like I have them? What am I missing here?!

jimmyblue

iTrader: (11)

The SLP has been "tricked" to look like a stock MAF
but the quality of that is suspicious (one cheap
resistor makes totally different pieces, look the same?).
It seemed "close enough" other than some fairly big
negative LTFTs back when I had one on there, but
the top end, who knows? But it is a bigger piece of
pipe.

Thing is, no matter what, 512g/sec is all you get to
tell the PCM about. If you go past that then you
have to crutch it (like by raising the PE to not-real,
but effectively-right enrichment at the higher RPM
(where presumably you would never be, without
a high MAP, so choose not to sweat the part-throttle
effects of lying about enrichment).

The SLP with resistor -will- indicate more air than the
Delphi base unit alone, at the 12kHz limit. But no more
than the stock Oreo MAF that is built to hit both PCM
limits simultaneously.

If you had the time and the air source you could put
the stock MAF and the SLP in a tandem tube, rig the
power and two frequency counters, set the blower so
the stocker reads 12000Hz and diddle the resistor on
the SLP until you get the same 12000Hz output. That
would put you to the same big-end cal point; taking a
few intermediate frequency points would let you hand-
fit the rest of the curve in Excel or something.

Then again, you want air, get the same sort of result
with a rat-tail file, cut and try until the SLP puts out
the same 12000Hz (a little dressing drifted my piece
to the point that a 3300ohm resistor was needed, to
get back to where the piece originally was with the
2700 it came with). Still want to get the midband
trued up and the curve is not any kind of straight
to begin with.

WAHUSKER

iTrader: (4)

Thanks Jimmy. Once more, you beat me over the head with the obvious (that I continously seem to forget) 12kHz = 512g/sec is max the PCM understands. So what we really need is a way to change that limit. I'm surprised HP Tuner (or someone) hasn't fixed this. Considering the mondo turbo cars that hang out on this board, I'm sure the need is there.

This must be the real reason why they run in SD mode.....I just don't want to because of all the fiddling you have to do whenever the conditions change. I want to tune it in & forget it.

muncie21

iTrader: (14)

The 'limit' is a limitation of the PCM or OS. 512 is the largest number that can be represented in binary for that register/table.

WAHUSKER

iTrader: (4)

So the data word is 9 bits? That is silly!

But I've been pondering.....the MAF reads airflow by measuring speed across the thermistor, correct? Meaning it's interpolating temperature into airflow. More compressed air = higher temps. IF that is what it's doing, then a larger MAF should slow the air down by increasing volume, or decreasing compression. So an 85mm MAF should help my PCM read the FI airflow more correctly.

Or am I way off base here? (really, I searched & couldn't find this discussion)

jimmyblue

iTrader: (11)

The MAF's local restriction will only change the relation
of cross sectional area and velocity. But the mass air
measurement here is just the cooling effect of air on
a resistor, and the electronics are trimmed to get the
right answer from each, whether you use one or the
other.

The MAF is just one little segment of a much longer
pipe, and it doesn't have a whole lot of weight in the
big flow picture I think. At least, once the screen is
gone.

The MAF doesn't sense the air temperature per se; it
"sees" the cooling power against a hot resistor and
works to keep that resistor at its setpoint temperature
(using a high-tempco material, maintaining a fixed
resistance in the bridge). More heat taken out meant
more air molecules doing the taking; their speed is
not important to this instrument, just the number
that rub up against the hot piece and take some
home.

It's just too bad about the bit limitation, and it does
not seem like a sane one, but I guess nobody at GM
/ Delphi ever figured that 500HP+ cars were their
problem.

muncie21

iTrader: (14)

I'm not sure how the number is represented in the PCM, floating point or integer, but if it's FP it has to be larger than 9 bits. Also, we don't know if the MAF word (16 bits??) uses some of the bits for other related functions.

WAHUSKER

iTrader: (4)

Thanks for the info Jimmy. It still seems to me that increasing the volume should slow the velocity down, and thus decrease the cooling affect. Although it could be like running too much oil pressure, where it moves so fast it doesn't have the proper cooling affect (& lubricating for oil), so it could actually make things worse. I guess I will just have to install the thing & see if it changes anything. Maybe I'll learn something.

And it would be normal from my experience with CANBus data for this to be a 16 bit word & use other bits for error flags or msg id #s or stauts bits. Sure would be a nice bit of the code to hack for all of us high HP guys. But I am slowly starting to grasp why all the tuners steer you away from after market MAFs.

SMOKINV8

iTrader: (6)

If you feel like doing some digging through the archive's, some time ago Harlan had his car set up with twin-MAF's like what jimmyblue mentioned. I think he used two stock MAF's, but I could be wrong.

Russ K

iTrader: (1)

It would be a lot easier to update to a 2bar sd os from HP Tuners and loose that restrictive 78 mm maf sensor. I have a 2001 Z06 cam/header car that is mafless.
Going mafless was a huge tuning improvement! I installed an IAT sensor & pigtail from a 2000 Corvette since the IAT is part of my stock 85 mm maf.

Russ Kemp

WAHUSKER

iTrader: (4)

Yeah yeah, SD tuning.....sadly that seems to be about the only answer. Problem is, if I tune it here, then drive to Nevada for an Open Road Race, or to Topeka for a Pro Street Race (both of which I've been comtemplating this year) then I have to re-tune for that air. Which really doesn't excite me much. Not to mention the air is cool here now & the elev is around 200', and come summer it will be hot & around 1500'. Call me stubborn, but I want to find a way....the MAF makes life too simple to just ****-can it.