CIS Ignition Tuning

[Daviboy]

Ok heres the deal got my cams back re-ground to 964 specs, have my 9.8:1 pistons coming. Should start the rebuild soon. My question is whats the ultimate ignition timing specs for my 3.0L SC? I have decided to stay with the CIS as it is/was working fine and I want to keep the motor as close to original as possible. Do I need to have my distributor re-curved or will it be ok as stock. I will be fitting an MSD 6AL box as well.

[Sigurd]

Suggestion: Get the programmable MSD 6 box. Then you can fine tune the curve by the help of a computer with a seriel port.

[Steve@Rennsport]

Davy,

Your flexibility with ignition timing is really based on your compression ratio (its high for CIS) and what octane fuel you will use. I would recommend that you check your AFR's to make sure you are not too lean.

[Daviboy]

Steve I have 95 octane at the pump hence using the 9.8:1 which is what the stock motor (euro) had. Another question how should the cam timing be set retarded or advanced?

[Steve@Rennsport]

I'm assuming you are using factory Mahle pistons.

Given the use of 95RON fuel, I would not use more than 32-33 degrees total timing. With 98RON, you have more leeway.

Cam timing affects where the power is in the RPM range so this depends how you use the car. Normal 964 timing is 1.26 and thats where I would set it.

[Daviboy]

Steve no I am going to be using JE pistons.. Car is a daily driver which sees very little track use

[Steve@Rennsport]

Originally Posted by Daviboy

Steve no I am going to be using JE pistons.. Car is a daily driver which sees very little track use

I would not use more than 30 degrees total timing unless you use 98RON fuel.

Porsche's CR spec using Mahle or Kolbenschmidt pistons was always higher than measured values and thats what afforded the flexibility with fuel & timing. With custom JE's made right to factory published specs, that detonation margin is all gone, especially with lean-running CIS engines.