CR of 2,4S pistons with a 2,2 crank

MaRu · 09-15-2015, 02:34 AM

A friend of mine is rebuilding his 2,2T and I am helping him with buying the parts needed. The original 2,2T pistons aren´t availble anymore. But the 2,2E are. -but not before next year which is an issue for him.Cylinders are no problem.
Does anybody know where 2,4S pistons will end in Compression with the 2,2 crank and the T heads?

Many thanks, Malte

Flat6pac · 09-15-2015, 03:13 AM

8.5 then 4 mm short on crank compressing..not much compression left
Bruce

Heinz911 · 09-15-2015, 04:13 AM

I would keep te original iron cylinders and have them honed to an overzise and buy custom pistons from JE or Woesner to match them.

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by MaRu

Does anybody know where 2,4S pistons will end in Compression with the 2,2 crank and the T heads?

Many thanks, Malte

84mm bore
70.4 stroke
69 cc chamber
22.3 cc piston dome
Equals 8.5:1 static compression ratio, stock 2.4 S
Change the stroke to 66mm and the CR drops to 8.03:1.
That ration is low but doable for a touring type 2.2 engine. The engine would feel pretty anemic.
Ken @ 911 Vintage Parts (760-731-4911) may have a reasonably priced, set of 911 2.2 E pistons to fit your requirements.
info@911vintageparts.com

MaRu · 09-15-2015, 12:02 PM

Thank you very much! Do you think that 2,2s pistons will work? I am a little worried about the dynamic compression with the T cams. But on the other hand the worst fuel we have is 95 octane...

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by MaRu

Thank you very much! Do you think that 2,2s pistons will work? I am a little worried about the dynamic compression with the T cams. But on the other hand the worst fuel we have is 95 octane...

If you use an extra base gasket .25mm your compression will be reduced to around 9.5:1 leaving you safer on the detonation front.

MaRu · 09-15-2015, 10:08 PM

Perfect, -thank you very much (again)!

Heinz911 · 09-15-2015, 11:52 PM

I also have S pistons with T cams. It runs great also on 95 octane, but had to adjust the timing curve because the standard 35 degree advance is a bit to much. I now have a 30 degree advance as this was original spec for S engine.