help deciphering over rev report CGT:
09-18-2009, 04:39 PM
#2
range 1 refers to number of ignitions (spark plug firings) that occur in the rev limiter range - not harmful.
range 2 ignitions occur when the rev limiter can't stop the madness, i.e. 5-4 downshift intended, 5-2 occured instead and clutch was released. less than 1k sparks in that range wouldn't worry me, sounds like someone just mis-timed a downshift by a hair. a drag race situation, however, wherein someone were going for a WOT 2-3 upshift and got 1st instead... that would be a different deal, but would typically result in thousands of ignitions in the upper range. and a broken motor.
29.5mm is about 50% of clutch - new is ~30.5-31.0, repl rec'd @ 28.0.
range 2 ignitions occur when the rev limiter can't stop the madness, i.e. 5-4 downshift intended, 5-2 occured instead and clutch was released. less than 1k sparks in that range wouldn't worry me, sounds like someone just mis-timed a downshift by a hair. a drag race situation, however, wherein someone were going for a WOT 2-3 upshift and got 1st instead... that would be a different deal, but would typically result in thousands of ignitions in the upper range. and a broken motor.
29.5mm is about 50% of clutch - new is ~30.5-31.0, repl rec'd @ 28.0.
09-22-2009, 10:44 PM
#3
Rennlist Member
+1 on what 'That Guy' said. Ask a good Porsche dealership what they think and if they would do the Certified Porsche Warranty on that car assuming it checks out normal otherwise.
There isn't much recorded data in the computer to help analyze possible engine damage. I believe the system only has the cumulative ignition count and time (in hours) of last ignition recorded for each range.
It would be nice if the computer logged more data because the range 1 and 2 ignitions always raise questions.
The spark plug ignitions happen at a high rate but I haven't worked it out for the Carrera GT engine.
As an example consider the ignition rate for the 996 GT3 six cylinder engine. At crankshaft revolution limit (electronic limit) of 8200 rpm, there are 410 ignitions per second. So even going a tad over the rpm limit just once equates to many ignitions.
The Carrera GT engine has an even higher ignition rate so it wouldn't take much time slightly over the limit to get 825 ignitions cumulative. There is also an engineering factor of safety on the over revs so it may take a high over rev to break the engine.
There isn't much recorded data in the computer to help analyze possible engine damage. I believe the system only has the cumulative ignition count and time (in hours) of last ignition recorded for each range.
It would be nice if the computer logged more data because the range 1 and 2 ignitions always raise questions.
The spark plug ignitions happen at a high rate but I haven't worked it out for the Carrera GT engine.
As an example consider the ignition rate for the 996 GT3 six cylinder engine. At crankshaft revolution limit (electronic limit) of 8200 rpm, there are 410 ignitions per second. So even going a tad over the rpm limit just once equates to many ignitions.
The Carrera GT engine has an even higher ignition rate so it wouldn't take much time slightly over the limit to get 825 ignitions cumulative. There is also an engineering factor of safety on the over revs so it may take a high over rev to break the engine.
