Relocating the AFM to after the turbo
Joined: Feb 2001
Posts: 29,798
Likes: 128
From: London, Ontario, Canada
Personally, I wouldn't do it. The AFM is not designed to take any pressure, and the high temps coming out of the turbo might be damaging to it. As I recall, it also contains a temp sensor, so the temps of heated compressed air might confuse the reading or compensation somewhat.
Originally posted by dcfc3s
One thing I'm fixin' to experiment with is moving the AFM to the intercooler piping. It's much less of a restriction than before the turbo, and it's a really popular mod in Japan - there are countless FC's making 400-500 hp with the stock AFM in the IC piping - gotta be something to it
.
You can upgrade to the '89-91 airflow meter - all you need is the airflow meter and the plug. I put it on my '88 Turbo and had NO problems - it started and ran just fine, made great power, you name it, with no tuning to the AFM signal or anything.
I really wish there was a "good" AFM solution for the RX-7. AFM's have a big advantage in that they calculate the volume of air directly. With a MAP based system, it estimates air volume by manifold pressure, throttle position, and RPM, with a set volumetric efficiency for the motor. When you alter the motor's volumetric efficiency, the whole map goes outta wack. That's why the FD guys have much trouble when upgrading their cars and need a computer early in the game. Same goes for a Haltech - you have to redo the maps when you make changes to the VE of the car, although it isn't as radical, since you're usually starting with a free-flowing system, not a choked-up factory system.
Anyhow, some food for thought.
Dale
One thing I'm fixin' to experiment with is moving the AFM to the intercooler piping. It's much less of a restriction than before the turbo, and it's a really popular mod in Japan - there are countless FC's making 400-500 hp with the stock AFM in the IC piping - gotta be something to it
.You can upgrade to the '89-91 airflow meter - all you need is the airflow meter and the plug. I put it on my '88 Turbo and had NO problems - it started and ran just fine, made great power, you name it, with no tuning to the AFM signal or anything.
I really wish there was a "good" AFM solution for the RX-7. AFM's have a big advantage in that they calculate the volume of air directly. With a MAP based system, it estimates air volume by manifold pressure, throttle position, and RPM, with a set volumetric efficiency for the motor. When you alter the motor's volumetric efficiency, the whole map goes outta wack. That's why the FD guys have much trouble when upgrading their cars and need a computer early in the game. Same goes for a Haltech - you have to redo the maps when you make changes to the VE of the car, although it isn't as radical, since you're usually starting with a free-flowing system, not a choked-up factory system.
Anyhow, some food for thought.
Dale
My cars louder than yours
Joined: Oct 2001
Posts: 1,969
Likes: 0
From: Augusta, GA
How in the hell can you just change over to the S5 map sensor and still use the S4 ECU? I dont see how this is possible, the man himeself says that its two completly differnt systems, the S4 ECU isnt programed to, as he put it, "estimate air volume bye manifold pressure, throttle position, and RPM, with a set volumetric efficiency for the motor". Unless somehow the MAP sensor has its own lil chip and both the map sensor and the AFM from each series sends the same signal back to the ECU for the same reading, i cant see how it works. Anyone is welcome to correct me on this, as i do not know for sure, it just doesnt make since. If you swap to the S5 ECU, then i might can understand...
Thread Starter
Senior Member
Joined: Nov 2001
Posts: 255
Likes: 0
From: Boothbay Harbor, ME
I don't think the s5 is all that different from an s4 AFM, correct me if I'm wrong tho. BEcause me and my good friend work on both our rx7s all the time, his is s5 with an s4 parts car and mine is s4. Our AFMs have been swapped and interchanged many times and Im not even sure which is which anymore. All of them work fine on my 87 TII. All in all I don't belive s4 or s5 have the MAP style AFM.
The issue here is relocating the airflow meter to the intercooler piping, and whether or not you can use the '89-91 AFM on an '86-88 car.
I've put an '89-91 AFM on my car -with NO SuperAFC tuning, just putting it on the car, the car started, idled, drove, and made GREAT power. I truly couldn't tell a difference between the two. I don't think I really made any horsepower, but the more compact packaging was the big plus for me.
The E-manage can correctly compensate for any (if there are truly any) differences between the airflow meters - you say your car is an '87, and you're using an '89-91 airflow meter, and it does the rest.
The air temp sensor's input to the ECU is identical between the airflow meters - it has the same response curve.
The biggest reason, IMHO, to move the AFM is restriction. As evidenced by the turbo inlet duct mod, a BIG, direct shot, intake to a turbo is best. You want to have a large reservoir of filtered air for the turbo to draw from - remember, for a given RPM, the turbo is literally FORCING tons of air into the motor, and it really needs a big pool to draw from. Turbo Formula 1 cars back in the '80s had VERY large inlet ducts that funneled into the turbo for this reason.
Now, once the air is compressed, it takes up a lot less physical space - that's why a 2.5" intercooler pipe is considered big, but it's WAY tiny for a turbo inlet duct. By this reasoning, the AFM will pose a lot less of a restriction to the turbo in the intercooler piping.
The air temp sensor's readings in the AFM piping is a good point, but that's something that could either be tuned out, or even have the air temp sensor relocated to the inlet duct of the turbo. This would probably require cannibalizing an AFM or finding another temp sensor that gives the same output.
Dale
I've put an '89-91 AFM on my car -with NO SuperAFC tuning, just putting it on the car, the car started, idled, drove, and made GREAT power. I truly couldn't tell a difference between the two. I don't think I really made any horsepower, but the more compact packaging was the big plus for me.
The E-manage can correctly compensate for any (if there are truly any) differences between the airflow meters - you say your car is an '87, and you're using an '89-91 airflow meter, and it does the rest.
The air temp sensor's input to the ECU is identical between the airflow meters - it has the same response curve.
The biggest reason, IMHO, to move the AFM is restriction. As evidenced by the turbo inlet duct mod, a BIG, direct shot, intake to a turbo is best. You want to have a large reservoir of filtered air for the turbo to draw from - remember, for a given RPM, the turbo is literally FORCING tons of air into the motor, and it really needs a big pool to draw from. Turbo Formula 1 cars back in the '80s had VERY large inlet ducts that funneled into the turbo for this reason.
Now, once the air is compressed, it takes up a lot less physical space - that's why a 2.5" intercooler pipe is considered big, but it's WAY tiny for a turbo inlet duct. By this reasoning, the AFM will pose a lot less of a restriction to the turbo in the intercooler piping.
The air temp sensor's readings in the AFM piping is a good point, but that's something that could either be tuned out, or even have the air temp sensor relocated to the inlet duct of the turbo. This would probably require cannibalizing an AFM or finding another temp sensor that gives the same output.
Dale
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Originally posted by Scott 89t2
I wonder how much PSI it could take before the plastic blew up?
I wonder how much PSI it could take before the plastic blew up?
.Dale
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