RPM limits of GM computer/ignition module?

[Ludis Langens]

Christopher Bennight wrote:
> 
>    My big worry is that somehow the limit is inherent in the pcm - e.g.
> to much overhead, etc.

The hardware in the PCM should be able to keep up at an RPM way higher
than a street engine will achieve.  Firing the injectors and ignition is
handled by hardware.  The software simply updates the hardware timers to
match new sensor conditions 80 or so times a second.  You could pull
onto a freeway in Kansas, get up to speed, throw a brick on the
throttle, pull the CPU out, and play space invaders until you reach your exit.

On the software side though, there can be a maximum RPM in the ECM's
calculations.  In older ECMs, the limit is 6375 RPM (255 x 25 RPM). 
Anything higher will be calculated as 6375.  Reports are that this
creates a soft rev limiter.  The software for a few applications uses
different scaling to go a bit higher.  For example, the 3.4 DOHC bumps
the limit to 7150 RPM.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


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