John

Sent you a PM.

Got it, thanks.

BTW, I seem to remember from my 993 ownership days they have a compression up around 11:1, right?

That's right, but they also have knock sensors that will retard the timing in any cylinder that is about to detonate.

Our older engines are limited to about 9:5:1 for single plug and 10:5:1 for twin plug if you run pump gas (93 octane).

The 964's had a stated compression of 11.1:1 if I recall.
I've only measured one 964 motor and the true compression was around 10.4:1.
-Chris

Yes, went back and checked, 11.3:1 in GT Purely Porsche...and some are supercharging on top of that.

One knock sensor per bank?

I don't doubt that. The point I was trying to make is that true compression ratio of these Porsche motors is make less than the stated compression. You cannot use the factory compression numbers as guide to what is "safe".

Knock sensors: Yes, one per bank with a "bridge" arrangement between the bases of the cylinders to a shared notch sensor.
-Chris