MAF mod
 

Hello everyone, I've been reading stuff on this forum for about 2 months now but just registered yesterday. I've seen a couple posts about putting a mustang MAF in an rx-7. This is one of the most common mods for porsche 944 turbo's. On that car this simple mod takes a couple hours and bumps hp from 215 to 300! I don't expect those results out of my gsl-se but we'll see.
I am an electronic tech by trade and to me this looks like it should be a fairly simple process. I'm getting together with an electronic engineer ( huge car nut ! )here at my work latter this week and we're going to see if we can figure it out. I'll let you know if we can do it since no one would respnd to those other posts. :bigthumb:

silly me, made it sound like you put a mustang MAF in a porsche! What I meant was converting from a barn door style to a hot wire. I really hope this will work.

I've been working on the same thing. Please post results here. There are several people who are interested.

I too would be intrested in this info.
Any results yould be greatly apreciated.

What kind of ballpark horsepower improvement would be expected on a 13B?

Have seen numerous posts on this subject as well, kind of getting the impression no one on the forum has ever tried the conversion. But looks like we may have a few interested candidates.

I've heard froma few sources that the AFM is the most restrictive point in the GSL-SE's intake tract. I'd bet that not only would it give ya a few HP on it's own, but it would allow any other improvements to express themselves a bit more. (Intake, exhaust, ect) I'd bet the motor would rev a tad freer as well, being able to breathe a bit better.

Just my .02, I could be wrong.

No speckamp, you're not wrong. Don't worry, I'll crack this one soon. I've been doing my homework for right now. The problem lies in how to fool the computer into thinking it's still reading of the rheostat in the vane airflow meter. Anyway, there are many other cars where this is a routine part of the upgrade process and I hope to make it that way for our cars. As far as what you can expect to see from this mod, it's almost hard to belive. Drivability will be improved, along with faster rev-up. Also it is correct that you will see more from this mod when you already have the basic mods. Also remember that you will have to switch air filter to a ford style to fit the new MAF, either that or make an adapter for you old intake. As far as HP, now don't laugh because I'm serious about this, I expect to see 20-25 rwhp on a stock engine. If you already have a full free flow exhaust and cone intake I expect more like 30-35 rwhp. That is with a new aftermarket MAF, not a junkyard one. Maf's are very sensitive and I don't like the idea of pulling one out of a car that already has 100K on it. Anyway, those HP estimates are defanitly on the conservitive side, but we'll see for sure when I get it done. I've still got a while untill that time comes. Let me know if anyone else trys this in the meantime.:D

How about aftermarket computers?
 

I the same vain. Does anyone know if there are aftermarket injections kits offered for the GSLSE? Seems like there are a lot for the 2nd Gen cars.

Something without all the smog device considerations. Do they have wiring harnesses for EFI that are more in line with racing?

And a programable computer?

Ok, I'm here to rain on the parade :(

You won't see a huge diff in the mod, true the AFM is a bottle neck, maybe 5HP. You have to rember the guys running the Carb conversions, they have removed the "bottle necks" and still when put up against a built EFI system, there is not much improvement.
When I put the modified 2nd gen AFM on my car. I found that it is going to be real hard top fool the ECU. I have thought of an idea that should in most respects work.

Mo Power Plan 777

Keep the stock AFM meter, it works, well for daily driving, overall, perf, will not change.
the mod is, to let more air in at Full Throttle, when its Wide open is when you need more air to get in, so if you had say in theory a blow off valve in reverse, so when the door is at full open, there is a way to trigger it to allow an incrimental amount of air to get into the intake via a second filter (smaller) thus it will still be creating enough suction to keep the door flapper open, and still allow more air in, the more it tries to suck the futher it will open the "blow off" valve to allow additional air into the system
It could be plumbed right into the intake and be triggered by a contact switch in the AFM and made to control and air valve? thus opening the "blow-off" valve

anyone? I really think this might work, no need to go thru all the ECU stuff which will be a real pain.

Sorry max 7, you're just not right about this one. Go look at the fourm pages of any other car where this is a common modification and you will see. Exaples = BMW 3 series, porsche 944, 84-88 couger/thunderbird. None of them EVER gain anything less than 20hp. Not ever. Also, I have driven cars before and after with this mod and you will be amazed at the difference in throttle response. You are right about the cpu though. That's where being an electronic tech comes in. See our cars use an active voltage output to read the resistance changes in the AFM. A cpu set up for a MAF is a passive system where the MAF does the conversion and the computer simply reads the change in voltage. I have to make up a converter for this to work corectly. It's not that hard, and I have the help of a few electrical engeineers to help. It will just take a little time.

sounds like a good plan. but you are all refering to the gsl-se's , i.e. fuel injected.... what about us earlier years with carbs..
would this still be a good upgrade to look into.. easier, or harder?? any thoughts..

Ok, here we go:
riffraff:
carbs don't have AFM's, so you guys don't need the mod ;)

The AFM is what tells the fuel computer how much air is entering the system so it can add the proper amount of fuel.

The carb does all this through some voodoo that escapes me.

Rotary-MG:
They make plenty of aftermarket fuel computers that would work with almost any rotary you can get. If I do my turbo-II swap I'm planning on a wolfems. If you goto their website (the australian one, not the northamerican one) you can download the manual and read up on the system. It's pretty simple to program and tune, and rather straightforward to setup. It also doesn't need a laptop like the haltech or a commander like the powerfc. (well, it comes with the "commander", and you can use a laptop)


Max7:
By removing the restriction of the FI, most well-tuned carbs I've seen are running in the 160's. That's 25HP over stock. I'm not saying that this is going to be the wonder pill for our motors, I certianly won't claim 20hp to the crank w/ this, but I'll bet if tuned well, it'll give a few ponys on it's own, a few more w/ an open exhaust and cone intake filter, and it'll probably improve fuel economy a touch by being a tad more accurate.

And the reverse bov idea worries me in one way.
the ECU thinks XX cfm of air is entering the system so it adds YY lb/m of fuel. If you add more to XX without adding more to YY you're going to run lean. Lean == bad, as I'm sure you know well. I'd be afraid to lean my motor out too much by adding extra air w/o the ECU knowing. Just my own concern.

---

There are plenty of ways to accomplish the goal of eliminating the AFM. The "easiest" is go out, buy a haltech e6k, wolfEMS wolf3d, powerFC, ect, and install it. These all use MAP sensors with air temp sensors. These determine the pressure at the manifold as well as the temp of the intake charge, thereby calculating volume. This is not only more accurate, but works better w/ turbocharged engines, and elimiates the restriction of an AFM / MAF. Of course, at the same rate, that's gonna cost ya like 1000, and then you have to tune it and all that bs.

I'm sure you could rig something up to simulate the signals of the OEM AFM by taking the signal from the MAF and create the signal the ECU wants to see, and I bet it'd be alot cheaper than a 1000 ECU, but it's probably beyond most of us here to build.

Now, if someone like rex alot wants to take some money from me and send me a little black box, my e-mail address works ;)

--matt

thanks for the clarification speckamp. that makes things a whole lot easier for me...

good luck

I'm not from Missouri, but someone needs to "show me" some dyno results. Feel free to post some links.

Seems as if this was “the” great mod to our 13B's we would have a bunch more info available on it, and/or the aftermarket guys would already have a conversion kit. Keep in mind the average –SE is already 16-17 years old, these cars have been around for quite some time.

the address for the MAF I will use is www.granatellimotorsports.com. You can go to www.powerhaus.com to read about a similar type of swap.

I wouldn't expect NEARLY as much of a difference as the porsche site claims, since increasing airflow when a turbo or supercharger is involved, is always going to net more hp gained than doing the same mod to a normally aspirated car. But it should be a noticeable difference.

I'm still really looking forward to hearing what happens with this.

this mod would be usless on a carby
 

this mod would be usless on a carby cause a AFM is a device that gives the computer info on how much air is comming in and regulates the amount of fuel accordingly.(am i right) and is very restictive so if we got it replaced we could use more creativity on making ariboxes like the carby guys. and have better flow.Carbys dont need one cause the carb does all the adjusting of the amount of feul

same thing iwas thinking when i read max 7s post.
You got way to solve this?

I agree with Speckamp, and am still interested.

But 20+ horse power on a normally aspirated 135hp (at the flywheel) seems hard to phantom. More power to ya’ll if you figure it!

exactly, even with the MAF, how are you going to get more fuel, when you send full open signal to the ECU?
If the stock ECU knows what max flow is for the AFM its still going to be the same as with a MAF. the MAF may be flowing more air, but it still thinks X air is coming from the AFM.
Correct me if I'm wrong, but doesnt the stock ECU adjust the fuel via the Oxygen sensor? except on Full throttle, when it uses a fuel map?
So either would work in crusing, since its constantly being adjusted. but under full Throt, it goes to a fuel map?

This is a fun convo, good to see all these brains working :)

ok, for fuel issues, possibly a Fuel Pressure riser, used on Turbo and Supercharger applications?
That way on stock fuel maps, more fuel with the increased air flow.

hmmm..... brain starting to hurt, hehe :)

Again you're correct speckamp. I don't expect as much for exactly the reasons you stated. I still expect decent gain, especcially when used in conjunction with other breathing mods. The reason is other NA cars also do this and see good gains. It's like you said POS, it seems hard to pathom that this would make that much differance. I think you answered your own earlier question, it's hard to phathom and maybe that is why no one has really bothered to try.

ok. I have to interject here with a stupid question, as I'm interested in the possibilities here...

Could someone describe the difference between AFM & MAF? I understand the concept of controling and measuring the amount of air to control fuel mixtures, but how do these device operate differently.

Along those lines, how does the ECU compensate in a forced induction system (i.e 13bt)? Not a stock setup mind you, but when ones goes for an aftermarket addition. There is more air in the system, and needs more fuel, but what controls this?

Sorry, halfa$$ed knowledge showing thru.. Thnx!

brain...awake...for..first..time..in..years :p
 

rx7gslse:
the AFM in the GSL-SE is a little door with a variable resistor on it, this is a terrable way to do what it's doing. Having the air push open a spring loaded door is kinda gay when it comes down to it ;) a MAF is basically a thin wire that has a current flowing through it. The computer measures how much current it takes to keep the wire a certian temp (100 degrees C I believe..), this relates directly to the amount of air passing by the wire. A MAP is a completely different beast. It measures the specific pressure of the air in the manifold (in either psi above ambient, or below for non-forced induction motors), that combined with a temp sensor can be used to derive how much air is entering the engine. This is obv. the best way to do it ATM, but it'd also be the hardest to adapt to the STOCK ecu. as I said before, for about a grand you can get an aftermarket ECU and not have to deal with this problem.

Usuallly aftermarket kits add a boost dependant fuel pressure regulator that turns up the pressure to the injectors as boost climbs, tho, if you have an aftermarket ECU, it can use a MAP sensor to detect boost, and adjust the fuel accodingly. (this is my last edit this post, I swear! :p)

hm, i'm not 100% sure what "max" on the AFM looks like electrically, I don't know if there's a way to tell the computer that there's "even more air than you thought you could get" coming in. But I bet most of your gains are going to be at less than WOT when you get the advantage of less air resistance and the higher precision of the MAF.

And a fuel pressure riser might just do the trick...

It'd be a good mod to combine with some sort of re-programmed ECU to take advantage of the higher flow of the MAF.

This is an intresting debate... want to dig out haynes manual and try and read wiring diagram :p

--matt

Sorry to start this thread and wake up all those sleepy brain cells.
Let me see if I can answer a few of these.
To rx7gslse- The afm our car uses has "barn door" in the path of the air. It's not unlike a throttle body. It's spring loaded and as more air presses on it it opens more. The door is connected to an adjustable resistor called a rheostat. the more open the door is, the less resistance. This is what the computer reads. A Ford style Mass Airflow Sensor is a 2 wire setup. The hot wire reads air temp, the cold wire reads air speed. Kind of complicated to write out exactly how the sensor reads and converts this info, but it does, and it's output is square wave signal that the computer reads. Turbo units with aftermarket computers use a Manifold Absolute Pressure sensor which is something else entirely.

To max7 and speckamp. You're right in you're assumtions about having to raise the amount of fuel as well as about what the cpu does with that info. There in lies the trick, and the key to unlocking the HP that I'm talking about with this mod. Like I said, I'm still working on it and haven't finished all the details yet. Yet.

Rex a lot,
What kind of volumetric increase would be achieved by your modification? I understand getting rid of the slow barn door for an increase in throttle responsiveness, but how much more air volume will this system allow? You can only suck or blow so much air through a given space, so how will this get you the horsepower gains you’ve mentioned. You can bolt up a huge carb on an engine, but there is a limit to how much fuel and air the engine can process, before you start having diminishing returns on your investment. Will the downstream systems be able to handle the added efficiency of your system?