Valve Cam Timing

I own a 1978 911 SC. Can anyone out there tell me what the correct measurement is for timing the cam for valve overlap. I have read that the cam can be advanced for better high end performance, or retarded for better low end performance. Which is best?

[This message has been edited by stormcrow (edited 08-30-1999).]

Advancing the cam timing, or lowering the setting, is a bad idea. It will move your power way up the RPM's, making the car pretty undrivable at lower speeds - not good for a car driven on the street, ever! On my 65 911, at a setting of 4.08, the power of my engine didn't show up until 6100 RPM!! That gave me about 900 RPM to drive within. That meant every time I went into corners during racing and the RPM's fell below 6000, I was a sitting duck until I slowly climbed up to the 6 grand RPM range. I reset the timing to 4.66 and the power now shows up at 2900 RPM. Much, much better. It now pulls all the way from 3000 to 7000 very strongly, and is easier to drive if I drive it around town.
The spec setting range for my car was 4.2-4.6, and I initially lowered it since I had the values reversed - lower it to raise the power band location, and raise the value to lower the power band location is the correct way!
I suggest you get a factory spec book for your car, and then decide if you like where the power shows up. If you do, then don't fiddle with the timing. You may not like the result, and it's a pain in the butt to reset it - the engine has to come out. And, don't go too far out of the factory range. The range provides a good ballpark, and you will notice a difference. When I went all the way down to 4.08, it was too far. 4.66 is a bit high for my engine and its setup, but that is the highest value I could get near the range, to get the cams to be the same on both sides.
I hope this helps. You may be able to learn from my initial mix-up! Be sure to get the values correct in your head, and accurately set both cams at the same setting!