CR of a '70 911T?
 

The tech specs say a '70 911T has a CR of 9.1:1, but after adding a 2.4 crank I measure it to be 8.27:1.

I just came across some random web page that listed the '71 T as 7.5:1, which would make more sense.

I quadruple checked all the measurements. The pistons are so flat that even with a deck height of 0 the CR only goes to 9.3.

Everything is stock except for the crank, so I'd expect the CR to be a bit higher than from the factory. Is the 9.1 value wrong?

Jeff

8.6 is what my Porsche 911 Red Book says. Es had 9.1, Ss 9.9.

Ok, that's closer. I still don't get how a longer crank lowered the CR :confused:

Could you check what the stock deck height was?

A 2.2T is 8.6/1

A 2.4T is 7.5/1

Theoretically, you should end up with 9.15/1 when you put that carnk in your engine. But Porsche has apparently over-stated their compression ratios. Pretty much every engine is at least a half point lower than advertised CR.

Thanks, that's really helpful.

Right now my deck height is .050", and the CR is 8.27. Reducing the deck height or cutting the heads will increase that.

Think the increase in CR is worth it?

Jeff