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In Reply to: AFM upgrade? posted by Ben on January 11, 2002 at 20:23:46:
Here's where the problem is: The AFM on the E28 M5 engine (and most all other fuel-injected BMW engines made in the 70s and 80s) all used a flapper-type AFM, which has a spring-loaded door inside the AFM. The more air that goes by, the farther the door gets pushed open. This is a huge bottle-neck in the intake tract. If you upgrade to a more modern Hot Film Meter (HFM) or Hot Wire Meter (HWM), you basically put an almost restrictionless 3" pipe in place of the restrictive AFM. The HFM or HWM (commonly referred to as Mass-Air Flow [MAF], actually is an air-mass meter [AMM]) uses either a thin wire or metallic film to gauge the mass of air rushing past. No door, just a very thin piece of metal.
The problem comes when trying to retro-fit. The old meter puts out anentirely different signal versus the new meter, so there has to be a signal converter, or else the engine computer doesn't have a clue how to interpret the AMM's signal.
So that's where Split Second's system comes into play. It uses 4 calibrations to "convert" the output of the new AMM to the old AFM. It doesn't match the curves exactly, but it gets pretty close. If you have it adjusted too lean (not enough fuel), you can burn valves, pistons, and basically blow the motor. If you run too rich, you get a loss of power. Proper tuning MUST be done on a dyno and on the street with an accurate exhaust gas analyzer. Since many people have blown up or damaged engines from improper tuning, many others think that you should avoid the upgrade.
But with proper tuning, you can unleash a load of torque in all ranges and HP on the top end. Even the low-torque E30 M3 engine benefits most in the 2000-4000RPM range where you normally don't get a lot of torque.
It's also worth noting that the E34 M5 only has 0.1L more displacement, slightly bigger cams (nothing major), 10.5:1 compression vs our 9.8:1, a few intake and exhaust changes, and an Air MAss Meter as standard equipment. It makes 59HP MORE than the E28 M5 in 100% stock trim. I feel that most of this gain comes from the AMM vs the old AFM.
JamesM
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