nrider42

I have searched this topic and found some conflicting and stale/dead information so I was hoping for a refresh that was applicable to my situation.

I have three different 944 DME's sitting in my garage and two motors to play with. All are from 8V NA motors.

1. Early 1985 ROW DME which came with my early 1985 euro car. The engine in this car has 10.6:1 pistons. I want to keep this car in one piece

2. Early 1985 USA DME which came with my early 1985 race car engine (now in a sad pile of parts).

3. 1988 924S DME which came with my 1988 924S race car engine. This engine has 10.2:1 pistons.

I ran the 1988 924S motor in my racecar last season in PCA SP2 and am working on it now in preparation for the upcoming season. Last season I ignorantly ran the engine with the early 1985 USA DME. There were reasons for this but not great ones. I had the car dynod at the end of the season and as I suspected it only made 129 HP and 133 ft-lbs. Stock header, stock intake, 93 octane. Leak down and compression are good (I don't have the numbers in front of me). I am planning on doing aftermarket headers, cleaning up the vacuum system and maybe a cold air intake (just for fun).

Now back to the DME, what are the differences in tune for the three different DME's? I am guessing by running the early DME with the late high compression pistons that I made a fat slow franken motor. Are the DME maps tuned for compression?

I now have a matching AFM for the 1988 924S DME and am planning on using that with the race motor along with an Autothority chip. Does that seem like a good match for the 10.2:1 motor? By adding the headers my intuition says I am going to lean it out. Will the DME mixture switch be able to accommodate this?

The competition is all doing custom tunes but my budget isn't going to allow that right now.

Any thoughts are welcome. These motors get more and more fascinating as I dig into the details. I would really like to find some good documentation for the DME programming. We are required to use the factory DME so no aftermarket toys are allowed.

Cheers,

Nate

wildcat077

I know for a fact that if you use a "late" DME on an early car , you also need to match it with a late AFM , not sure about the chip though ... some just
allow you higher RPM's but without a cam your powerband will stay the same and you'll be loosing HP over 6000 rpm.

For what it's worth , not many top runners are "stock" in SP2 , i figured that one out over the years ...

V2Rocket

US DME with the lower compression might have more aggressive spark timing than the Euro DME (speculation).

might even be that you were running over-advanced and wasting power.

be neat to hook up a euro DME to a scanner thing and get its ignition targets to compare.

J1NX3D

Do you need the DME or just the chip for that? My stock '86 RoW chip is sitting in a box at home (the box my 944MAX chip came in).

V2Rocket

im sure there's a timing light setup or something along those lines that could be used while on a dyno.

nrider42

Well, I will be on the dyno again in the spring. I guess I will swap them around and see what happens. I do not have the capability to read the chips but I do have a timing light. That might be interesting information. What does the timing look like across the entire throttle range?