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Re: M3 Overrev
Gary Bossert wrote:
> I can't be sure of this (Jim C. do you know?) but a reliable source
> told me that if the car is over-reved the BMW dealer computer can tell
> once it is linked to the car's brain. Supposedly this info is stored
> in the brain. Sounds crazy to me but I wouldn't put it past them
> (BMW). IMO if you over-rev your engine it is your fault not BMWs and
> they shouldn't have to pay for it because you don't know how to drive
> or put in a chip with a ridiculous rev limit.
Some additional info related to the above comments. I race a '95 Ducati
955 Corsa. My sponsor (Pro Italia Motors, Glendale, CA) has a data
logger made by Fuel Injected Motorcycles in Australia. This unit
consists of two small black boxes which are mounted behind the fairing
for practice sessions and some races.
The data logger is connected to the ECU and to a lambda probe in the
front cylinder exhaust header. Suspension telemetry and wheel rotation
sensors can also be fitted. After a track session, a laptop computer is
connected to the data logger and downloads whatever data the unit has
been set up to record.
One of the more useful functions is a graph showing exhaust gas oxygen
percentage for all combinations of throttle opening and engine RPM.
This chart shows exactly where, and by how much, the engine is running
rich or lean. Next we pull out the chip, pop it into a hand held EPROM
burner, and reprogram the chip to correct it. The whole process takes
about 15 minutes, and is repeated two or three times to get it really
dialed in.
Among the many things recorded, even with the most basic setup, is the
complete range of engine RPM's for the entire session. This info is
plotted on a graph (x = time, y = RPM) and printed out. It's very easy
to spot where and by how much any overrevs occurred; I've been chewed
out more than once!
Of course the amount of data recorded is limited by the amount of memory
installed in the data logger. But it seems plausible that the ECUs in
newer cars could be set up to only record overrevs when they occur, as
opposed to continuous recording. This would get around the memory
problem. I don't know if this is the case with BMW, but the technology
is certainly readily available.
The only ways to overrev a rev limited engine are to change the chip
(which voids the warranty), downshift to a gear which is too low for
your road speed (driver error), or a missed shift. A missed shift is
usually driver error, but sometimes results from a transmission
problem. If there is a transmission problem with these cars, that could
be grounds for warranty repair. Of course it may be possible to get it
repaired under goodwill anyway, depending on circumstances.
Just a few thoughts from a motorcycle racing BMW enthusiast. Hope it's
useful to someone.
Gregory Prinsze