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CIS Ignition Tuning
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.
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Suggestion: Get the programmable MSD 6 box. Then you can fine tune the curve by the help of a computer with a seriel port.
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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. |
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?
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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. |
Steve no I am going to be using JE pistons.. Car is a daily driver which sees very little track use
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Quote:
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. |
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