MAF Transfer Function Theory...

[hioc1098]

Help me to understand the MAF transfer function difference between a 90mm LMAF and a Flow Tube. I’m not necessarily new to the game. I was one of the first group of users for the SCT Pro Racer Package (98GT with a Mach I engine transplant). When I was using that, it was fairly simple to change Ford-style MAFs and injectors. All I needed to do was plug in the transfer function of the MAF I was using (typically a 90mm LMAF), plug in the injector value file for whatever injector, and fine tune the curve.

I have zero experience with blow through style MAFs like the Flowtube. However, I’m getting ready to use one with my turbo kit on my 94. It’s my understanding that the MAF will come calibrated to the 42lb injectors I’ll be running. Theoretically, I can just plug them in and run the car, because the MAF’s “calibrated” to the injectors. Obviously, I won’t do that, because the timing will need to be messed with (amongst other things).

Now, here’s the question. If I use my programmer of choice (either Tweecer or SCT), and I input the transfer function provided with the MAF, would it not be starting from the wrong transfer function? In other words, by inputting the 42lb “calibrated” transfer function that’s intended to trick the computer into working with the 42lb injectors, I’ll be working with values that are skewed. In my peanut brain, I’m thinking I’d either need to get the transfer function for a MAF (flowtube) that’s calibrated for 19lb and fine tune the curve like I normally would, or load the injector values for 19lb injectors – definitely not right. Otherwise, it’ll be really off. Am I making any sense? What approach do you take with a transfer function that’s designed to “fool” the computer into working with a different injector size?

[Dale McPeters]

Since you have the SCT Pro Racers package I would visit the
hidden forums that they have and ask Jerry W. this question......

[hioc1098]

Originally Posted by Dale McPeters

Since you have the SCT Pro Racers package I would visit the
hidden forums that they have and ask Jerry W. this question......

I could probably do that, but there are two issues. First, I sold the PRP with the car, so I no longer have it. I haven't decided if I'm going to go back to SCT and pay another $800 for the PRP for my car, or look to the Tweecer. I still have access to the forums, but that leads to the second issue.

For the last couple of years, Jerry really hasn't posted much in the forums. I know he's very busy, but I really haven't seen too many posts by him as of late.

FWIW, I'm not sure if your reply was a "tongue in cheek" reply. I don't want to start a which is better thread. I don't have an issue with either and they both have challenges. I honestly have read a lot of the Tweecer threads and used to read a lot of the SCT threads. In my humble opinion, it seems the Tweecer has a better base of folks who "appear" to try to help those who post questions. The SCT stuff, on the other hand, definitely has better documentation. They both serve a purpose, though.

Also, because threads cannot show tone. Please understand there's no sarcasm intended with any posts I make and there are never any personal attacks by me. I'm just a fairly laid back guy who likes to understand the theory of things. Just thought I'd throw that out before anything I write is misconstrued.

[Italian LX]

Originally Posted by hioc1098

Now, here’s the question. If I use my programmer of choice (either Tweecer or SCT), and I input the transfer function provided with the MAF, would it not be starting from the wrong transfer function? In other words, by inputting the 42lb “calibrated” transfer function that’s intended to trick the computer into working with the 42lb injectors, I’ll be working with values that are skewed. In my peanut brain, I’m thinking I’d either need to get the transfer function for a MAF (flowtube) that’s calibrated for 19lb and fine tune the curve like I normally would, or load the injector values for 19lb injectors – definitely not right. Otherwise, it’ll be really off. Am I making any sense? What approach do you take with a transfer function that’s designed to “fool” the computer into working with a different injector size?

If you have the transfer curve, then all you would need to do is enter it into your tuner and make sure your injector slopes are set to what size injectors you are using.

What size injectors are you using?

[hioc1098]

Originally Posted by Italian LX

If you have the transfer curve, then all you would need to do is enter it into your tuner and make sure your injector slopes are set to what size injectors you are using.

What size injectors are you using?

What effect would that have on load, though?

[Dale McPeters]

Originally Posted by hioc1098

What effect would that have on load, though?

Load will be skewed. You will have to correct this in the tune.
It will depend on the year model of the EEC for how this will
be accomplished. You can also tune it the way that SCT does
and just build a curve etc. as you stated above.
Just remember that on some year models there is always more
than one way to skin a cat.....

Also my post was not meant to be a "tongue in cheek" reply as
I thought you still had the SCT Pro Racers package. If you still
had it that is what I would use but since you do not then at this
point and time the TwEECer is probably the next best option.

[hioc1098]

Originally Posted by Dale McPeters

Load will be skewed. You will have to correct this in the tune.
It will depend on the year model of the EEC for how this will
be accomplished. You can also tune it the way that SCT does
and just build a curve etc. as you stated above.
Just remember that on some year models there is always more
than one way to skin a cat.....

Also my post was not meant to be a "tongue in cheek" reply as
I thought you still had the SCT Pro Racers package. If you still
had it that is what I would use but since you do not then at this
point and time the TwEECer is probably the next best option.

Thanks. I wanted to try to avoid building the transfer function from scratch, because that can be time consuming and I wouldn't necessarily want to do it with the turbo throwing boost at it. I've heard of folks using the SCT meters in a blow through configuration, but I'm a bit worried about pegging them without an extender. I've got about a month before my kit will be done, so I have a little time to find the right solution.

I only asked about the tongue-in-cheek, because there are some who have issues with one software or another. I'm more of a "use whatever I have to" person. The good thing about using the SCT first is if I go to a Tweecer, the learning curve will be a little less than if I was brand new. The only thing about SCT that I don't like is the $800 price tag and it doesn't datalog much on the 94/95 cars. The issue I have with Tweecer is the apparant lack of updated releases and lack of documentation - but the forums are really making up for a lot of it. Either will probably get the job done, though. I just need to do it.

Thanks a lot.

[hioc1098]

Originally Posted by Italian LX

What size injectors are you using?

I missed this one. I'm using 42lb injectors. It's a 94 GT with a T70 turbo and a .68 a/r.

[Dale McPeters]

Originally Posted by hioc1098

I missed this one. I'm using 42lb injectors. It's a 94 GT with a T70 turbo and a .68 a/r.

Since it is a '94 model the TwEECer-RT will work just fine.
If you are using the AOD-E tranny you will have to adjust the
shift points etc. etc. If this is the case then I would suggest
that you get in touch with Barney on the eectuning.org site as
I think that he is running one in his car....
I do not mess with the tranny functions in the '94-'95 cars so
I would be of no help in this area. If it is not a 3-5 or 6 speed manual
or a C-4/6, 2 speed power glide auto then I do not mess with it
at all........old school you know.......

[hioc1098]

Originally Posted by Dale McPeters

Since it is a '94 model the TwEECer-RT will work just fine.
If you are using the AOD-E tranny you will have to adjust the
shift points etc. etc. If this is the case then I would suggest
that you get in touch with Barney on the eectuning.org site as
I think that he is running one in his car....
I do not mess with the tranny functions in the '94-'95 cars so
I would be of no help in this area. If it is not a 3-5 or 6 speed manual
or a C-4/6, 2 speed power glide auto then I do not mess with it
at all........old school you know.......

Thanks. I'm running a 5-spd, so things are quite a bit less complex. I've been looking around and it appears my only shot at getting a Tweecer is to find one used. Everyone else appears to be sold out. My decision between SCT and Tweecer may have already been made for me. Thanks for the help.