Problem is, above 5000 rpm it just runs out of poop. My e23 B9 Alpina ia WAY faster, and even my stock 535is easily beats the M3. THIS should NOT be, right? I mean I love it, but it makes my buddy NUTS!
The exhaust is new (after the cats, it joins a single 2 1/2" and out through a big Flowmaster) and the back pressure is below 1 psi at all rpm as measured between the headers and the cats. The 2 1/2" flows the same volume on paper as the 2 smaller pipes from the cats.
All the sensors (TDC, RPM, ECU Temp, AFM Temp, Throttle Pos'n) have been replaced or checked, and a second AFM performs just like the first. The sensor resistances were checked right at the ECU plug, so the harness is OK, too. The wires and plugs are new, and the car idles smooth as a kitten. The O2 sensor has NOT been checked, but we tried runs with/without it with no difference. Since at full throttle, it is ignored by the Motronic ECU anyway, so that shouldn't cause a problem iven if it's bad.
The fuel pressure is right on, and stays at 43 psi even at 6000 rpm under load (we left the gauge hooked to the fuel rail with a long hose that we hooked under the wiper when we drove the car so we could read it while on the road).
My buddy even secured a "chip" to try to see if it would help. It is a "ERT" (European Racing Technologies) brand chip. I know nothing of this chip except that it increased the idle speed a tad, but didn't help the power at any rpm or throttle pos'n. I would have recommended a JC chip, but I don't think this is the problem.
The engine feels lean above 5000 rpm, but even tweaking the AFM by recalibrating it (messing with the spring tension) makes no difference (except it does affect the idle/midrange mixture and throttle response).
The compression is excellent, and I doubt the engine is worn or the cams bad (though we didn't check the valve lift with a dial indicator yet).
It just seems to me that at least in the lower gears this engine should SCREAM toward the redline rather than poop out at 5 Grand and struggle to redline. It is not "rough" at all, just kind of gutless, kind of like it's not flowing enough fuel.
Can anyone shed some light on how the engine SHOULD pull past 5000 rpm? I don't have a clue, but with that engine, and a 4.11 rear end I thought it should be a goer. I would hate to think the //M3 legend is all talk :-)
Also, any suggestions for troubleshooting would be most appreciated.
e23 B9 Alpina
(But NO e30 yet)