Porsche Replacement CDI

[Martin]

Hi,

When replacing a twin spark porsche`s 2 CDI`s with 2 Motec "porsche replacement" CDI`s, how will the RPM limiting be done?

I have done one such a car and both Motec CDI`s RPM limit is set to 6500 Rpm (done at motec prior to shipment). The problem is that the car revs through the RPM Limit, so effectively its not fully functional. I think that the problem is that the randomiser effect will have the 2 CDI`s cut separate cylinders so in effect some cylinders still get spark even though limiting is active. Is there is a way to solve this problem?


Thanks

Martin

[DarrenR]

Hi Martin,

The maximum RPM for this CDI is 20000rpm! It can be lowered but this is not a rev limit. It is to protect the CDI so if it receives two triggers too close together it will miss that spark and spark the next time. So if you had them modified so it started missing at 6500 rpm it would drop every second spark until it revved to 13000 where it would drop more. Being a twin spark setup, the two units could cover for each other like you're suggesting and it would seem like there was no cut at all.

From what i can find out, the actual rev limiter used by Porsche is either a separate box or a centrifugal switch in the rotor button!
The other way to do it would be by cutting the trigger going to the CDI units as this would synchronise the cut.