What determines the engine timing?

[Adelaide901]

I have a 2.2 litre 911 T engine with e cams.

My questions are:
(1) What determines the timing value for an engine? Is it the cam profile? (wow - do I sound like a newbie?)
(2) What would the proper timing be for my engine?

Thanks in advance

[911st]

Look up the factory spec.

How much timing a motor will take depends on a lot of variables that together must be tested to see what is effective.

Compression, position & head profile, cam profile and timing, operating temperature... all effect ignition timing.

There is also a ignition timing curve as the effective timing changes with load and rpm.

On an older cars there are weights, springs and vacuum canister/s in/on the distribuitor that control the timing curve.

[SP2]

It is the cam profile. That is my guess. The timing recommendations for the same engine are different with different cams.

For example, my stock SC engine has a timing of (I think) 1.1mm for stock cams, but 1.26 for my 964 cams.

[911st]

More aggressive cams lower the effective compression ratio.

A lower compression ratio slows the burn rate and requires more advance.

Higher rpms require more advance.

If you have the original Pistons and compression I would start with the T specs and distribuitor. You could fine tune it on a dyno from there.