Wallyman

iTrader: (1)

(also posted at CZ28.com)

Background:
Running a 94 B-Body Roadmaster LT1 (in a Mazda RX7). As part of the build, I put together a custom CAI to fit around the various obstacles I have, and had to add electrical tape to the MAF to get it to fit 3.5" intake couplers (which I thought was odd at the time...). Drove fine, until the tape got hot, slid and covered about 1/4" around the inside of the MAF, restricting airflow enough to make a noticeable SOTP difference. As part of fixing that, I stumbled across the fact that the B-body MAF is 3.25", but everything else is 3.5". Having felt the noticeable increase in HP from a tape-restricted 3.25 to unrestricted 3.25, I want to go the next step to the 3.5" off the F-body.

So... (Here's where you all start yelling at me) I picked up a ported/descreened f-body MAF on the cheap (yeah, I know, don't do a ported MAF, it messes with fuel tables, etc). My justification, however, is that since I was already going from 3.25" to 3.5" (from roughly 8.3 in2 to 9.6 in2, or about 15% increase in area) I figured a recalibration is in order anyhow.. so might as well do a ported/descreened since the programming involved is likely the same. That's my justification, anyhow, and I'm sticking to it!

So, after initial swap, the car idles fine, but sounds a bit.. lumpier. I can't get moving without it trying to stall, and it's very rough up to mid-rpm range then smooths out. Eventually (10+minutes) it will sort itself out enough to be relatively driveable (and the idle becomes noticeably smoother as well), but I still feel a tip-in stumble and everytime I drive the car the learning process has to start over. So it needs to be reprogrammed (was honestly hoping it was going to learn on it's own.. oh well).

So, how does a guy go about recalibrating? I am using the standard 94 B-body PCM, programming via TunerCATS and logging via EFIlive V4. I've tried doing searches but am not finding the answer... any help appreciated!

Wallyman

p.s. yes, I know I *should* use an unmolested F-body MAF, but regardless I am fairly certain that molested or not, any F-body MAF will require a programming change.. so if you are of the camp that says ported = bad/PITA/more work for no reason, that's cool.. but please go full circle and help me run an unmodified one! That means I need a stock F-body PCM program to snag values out of (and I need to know what values to snag).

ss.slp.ls1

iTrader: (36)

If you are using a '94 B-body PCM then I would use a stock B-body MAF. Use a plubing coupler that will connect 3.5" to a 3.25". Simple as that, no recalibration needed.

Wallyman

iTrader: (1)

That defeats the point. There's a reason the F-body had the bigger MAF...

I understand the suggestion, but I'm fairly sure the 3.25" is restrictive (otherwise you'd have one on your F car from the factory). I will be changing heads (at minimum) to the f-body aluminums, with a cam.. so I am going to be where a stock F car would be or higher. If it's not restrictive, why did the 285hp cars get a 3.5" instead of the 3.25" that the 260hp B-bodies got?

I know someone can explain how to do it.. or point me to a map file to raid the values out of. I know it has to have been done, there's too many ported MAFS out there for it not to have been sorted out.

Wallyman

ss.slp.ls1

iTrader: (36)

What makes you so sure? Fact is that the stock MAF is good up to 500rwhp or so. So I would imagine that your stock 3.25" B-body MAF is NOT a restriction. Save yourself the tuning headache and run the stock MAF and concentrate on things that will provide real results.

Wallyman

iTrader: (1)

Couple of responses.

First, Here's my subjective 'proof'.. FWIW.

The car ran fine, would spin tires in 2nd all day long. The tape restriction (about 1/4" ovelapped) made a noticable and consant loss in power, to where it would no longer spin the tires in 2nd.

So, if restricting a 3.25" to a 3" makes that big of a difference... why can't I make the assumption that moving from 3.25 to 3.5 would be a good idea when the F cars had the 3.5" stock? (No, that argument doesn't go so far as to say "well then 6" must be great".. I am basing it on the fact the F got a 3.5" stock)

Second response:

"The stock MAF is good to 500hp".. which MAF, the 3"/3.25" on the B-body or the 3.5" on the F-body? If you say the 3.5"=~500hp, ok, then why don't we say the 3"/3.25" is maybe good to 400.. sooooo.. why isn't the F-body equipped with a 3.25"? Stock was 285/305hp. Sure, the B has different heads and cam, but my end goal is to be like an F car so I think the 3.5" should be part of my setup.

Third comment:

Been searching and searching to find the CFM on the 3.25 (called a 3" in some cases - see here: http://www.turbobuick.com/forums/795049-post8.html) but finding nothing. I have found the 3.5" descreened flowed 719cfm (http://dtcc.cz28.com/flow/index.htm) but I got nothing on the B body one or the stock 3.5" F one. So I have no way to compare what the stock one I have flows.

I can appreciate the arguement "if it ain't broke, don't f-it up" but having seen the decrease in power on the 3.25, I'm feeling like there is gains to be had going 3.25 to 3.5.. plus there must be a reason the "performance" cars got the 3.5".

Final comment:
Ignore the ported/descreened portion of the issue.. I honestly don't care if it's stock or ported. I want a 3.5" because I believe there is merit to the size over the one I have. So if I buy a bone stock 3.5", I have the same problem.. I would have a larger MAF that is flowing differently than the PCM thinks.

So, my plea is to help me to retune the car to use a 3.5" MAF. If someone points me to the stock 3.5" MAF info I need, I'll probably dump this ported one and get a stocker and be happy as a clam.

Wallyman

ss.slp.ls1

iTrader: (36)

I didn't want to read that long response, since you have your own logic, here's mine...

So you had some mocked up tape thing that allowed you to couple your 3.5" piping to your 3.25" B-body MAF and it worked well. Tape came loose, and restricted your MAF, i.e. the incoming air cross section was smaller than the computer is tuned for...duh, of course you are going to notice a difference.

Now you want to swap to a 3" F-body MAF, and you will have to recalibrate your PCM for this new larger MAF, i.e. the incoming air cross section is larger than what the PCM is tuned for. Now once you recalibrate the PCM will it perform ok, YES, but will it be any better than the way it was before, I bet NO.

IMO you are wasting your time. Like I said, look for other areas of improvement.

buffman

iTrader: (9)

the B-body MAF is 3" not 3.25, just FYI

You have to change all of the MAF calibration tables in the tune for the new MAF. I could give you the base or close to base F-MAF tables, however with a ported unit, there's not telling even if those will be right.

Wallyman

iTrader: (1)

I'll take the base/close tables if you have them, that would be fine.

Wallyman

Wallyman

iTrader: (1)

So, you are saying that with a properly calibrated PCM to MAF, I'd see the same performance up to ~500hp with a 3" and the 3.5" MAF, right?

Wallyman

xx_ED_xx

iTrader: (17)

I understand what you are getting at. Unfortunately only tuning experience I have is speed density. I de screened then ported my maf on my f body. I really couldn't tell if there was a difference. But at one point i was parting out the car and some one wanted to buy it. well since i knew it would still run with out it i sold it. Sure enough the car ran better with out it. Probably something to do with the base tune in pcm. Put a straight pipe in its place and see how it runs. Of course if you have a the ses light hooked up you will get a code for maf.

ss.slp.ls1

iTrader: (36)

That's what I'm saying.

Wallyman

iTrader: (1)

Fair enough..

So why did the F car and Vette get a 3.5"? Has to be some reason GM tooled up a larger, different part... right?

Wallyman

(buffman - I'd still like the code you have for a stock-ish 3.5", please!)

ss.slp.ls1

iTrader: (36)

No idea. Fact it that you have to be moving A LOT of air before your stock MAF becomes a restriction and there are many other areas that would be a choking point first, like stock heads.

Wallyman

iTrader: (1)

Wish I was in the needless aftermarket MAF business.

Well, if I can't get my hands on some stock 3.5" MAF calibrations, I'll end up either manually trying to calibrate (I eventually found some directions here: http://www.camaroz28.com/forums/show...=MAF+reprogram) or I'll just run that 3" I have.

No doubt, the stock iron heads and stock B body cam are an issue right now.. hope to remedy that soon enough. Need to solve a driveline vibration issue first, tho.

So, anyone willing to give me a stock F body map from a 6 speed car, 94 preferred? Or even a screenshot of the table values?

Wallyman

96capricemgr

iTrader: (1)

You are making LOTS of poor assumptions and making absolutely no effort to understand anything.

The b-body was tuned for 87 octane and was grandpa quiet intake and exhaust. There are your reasons for the lower power rating.

Stock for stock the iron heads actually flow MORE than the aluminum because they were designed a little later using lessons learned.

In bolton form the b-body engine makes about the same power as the f-body and Vette. It actually looks more like the f-body cam was designed to hurt very lowend thasn it was to make more topend because like I said the b-body in bolton form makes about the same power.

Far as your evaluation of the MAF thing, anything that screws up steady even flow through the MAF messes up it's ability to read that probably cost you power, not the restriction you think it caused. Put a stubby cone filter on the MAF with a inverted cone in the end and it wont read right because the inverted cone causes the flow to be unevenly distributed as it passes through the MAF.

I strongly suggest you do some reading on exactly HOW the MAF functions and then you might understand why porting and tape haning in front of it are bad things.

Your, "I know I am doing this wrong but tell me how to do it anyway", is unlikely to inspire many competent folks to help you.

Wallyman

iTrader: (1)

Actually I am trying to understand but the typical "just put it back to stock, period" answer, while perhaps correct, doesn't teach me anything.. it tells to me to not ask questions and to just go away. Can't do that, I want to understand.
So the B cam (being different) is essentially moving the powerband lower, correct?
I have been reading quite a bit, and understand the basic function and method. Air flow is calulated by measuring air's ability to cool a heated wire via a know diameter of space with the screen acting as an air-equalizer so that any air measured is a true known percentage of the total air.... simplified but that's how it goes, yes? Descreening raises holy hell with even flow, and porting raises hell with the known diameter of air involved. Correct?
I feel that's a little harsh.. I came in thinking that a 3.5" was a viable upgrade and would require a MAF recal.. and if I am already forced to do a MAF recal to use a 3.5" I might as well do a ported unit too. I genuinely thought I was doing it right (upsizing from 3 to 3.5.. ported is irrelevant in this case) based on an apparent wrong assumption regarding the tape restriction. Had I not mentioned porting at all, would I have gotten the same sort of responses? Dunno... but for them being a bad idea, there sure aer a lot of the damn things around.

The fundimental question I was asking is "I want to go 3" to 3.5" MAF and I need help to recalibrate the PCM to use it". Your response (which is the best so far and the most helpful) is "the stock B body MAF is fine, you won't see any gains because the B motor is essentially an F motor once bolt ons are applied". So, based on that, I'm going to sell this ported MAF to some other fool and move on with my life (I really DO have other things I'd rather work on!) I saw the tape as a restriction, not as a turbulance-inducer.. and based on what you are saying, that's where it all went south. Had I seen it as a turbulence inducer, I never would have gone done this path, and my pie hole would have remained shut, my wallet a little fatter and my life a little less wasted on pointless pursuits.

Soooooo, Anyone want to buy a slightly used 3.5" ported MAF?

Wallyman

ss.slp.ls1

iTrader: (36)

Sounds like you are now on the right path. Now it's time for heads, cam, bolt-ons.