Compression with 2.2S pistons
 

What compression ratio can I bank on with the 2.2S pistons with the longer 2.4L crank and 2.4L T heads? is it above 10.0/1? (I hope not as its too late for twin plugging.)
Thanks in advance,
Nabil
p.s. stock 2.4L rods as well.

Installing a 2.2 piston on a 2.4 crank 70.4 mm will give you a static compression increase of .5 points of compression.
Of course you must measure you components to get a true compression calculation but if the 2.2 S piston is claimed to have 9.8:1 on a 66 mm crank that same piston will have a compression ratio of 10.3:1 on a 70.4mm crank.
You can lower this compression by simply adding to the cylinder base gaskets which will increase the deck height measurement.
Because the hemi chamber configuration of two valve 911 engines already has a propensity toward detonation even at 10:1 fuel quality I.E.. octane and distributor curve become hyper important.
When it comes to compression we tent to error or lean toward if you will, a safer level of compression.

I'm using a '70 E distributor....How does this particular curve weigh in on the equation? As the whole thing is together I may be running around with a glove box full of octane booster. How annoying.
Thanks,
Nabil

Henry,

Any thought on the affect of using the less desirable 2.0L "T" heads with the deeper combustion chamber?

Thanks!

The stock 2.0 T heads are totally incompatible with 2.2 pistons. The Valve angles are wrong and the chamber diameter is too small. The extra depth and small diameter has the same volume so there is no change in compression.
The deeper chamber exacerbates the detonation issue.
All together a very poor option.
Can they (2.0 liter heads) be machined to fit? Of course, why bother.

Thanks for the info. I guess that supports the general undesirability of these earlier heads!