911 2.2 to 2.4 E or S pistons?
 

I was looking in the rebuil book deciding on my new engine configuration. I luckily have access to both a set of E and S 2.2 P/C's and was considering stroking with the 2.4/2.7 crank.

In Wayne's book he recommends using both of these setups but states that the E pistons /2.4 crank give a Comp. Ratio of 10.1 and the S pistons give a CR of 9.8. Can this be right?

I would prefer to use the S pistons as I already have them where I would have to buy the E ones. Also is there a rod difference?

Re: 911 2.2 to 2.4 E or S pistons?
 

What sort of gas do you have access to? What sort of cam will you be using? Will you be twin-plugging? This will have a big impact on whether you have enough CR or too much.

Quote:

I would prefer to use the S pistons as I already have them where I would have to buy the E ones. Also is there a rod difference?

You'll need to use the 2.4/2.7 rods with the 70.4 mm stroke 2.4/2.7 crank shaft.

I can get good pump gas (los angeles area) I don't really want to twin plug. That's why i was leaning to the lower CR. I was just surprised that the book stated that the S pistons would give a lower CR than the E pistions. I will customize the cam grind to the motor, again not sure here, probably an E or S grind.

Even after you search on this topic it still remains a little confusing as to whether 2.2S pistons with a 2.4 crank is o.k. on todays gas without plugging etc.

There are some very knowledgable people on here that hopefully will chime in????

i read here somehere that the CR in porsche engines was generally overstated - so the actual CR of 2.2s pistons in a 2.4 is below what it should calculate out to if the original 2.2 CR was as stated... 2.2E pistons will have a lower CR in either application.

Plenty of people have done this upgrade on 2.4's on this board and i have not seen a warning of it yet. I think you have to be careful if you a re building up a motor from different years that may have been machined etc that could bump up the compresson further.

I am replying on this hoping i am right....

I have 1000miles on this rebuild - 2.2s pistons 2.4crank 69E cams 2.2 T heads.

single plug using 96 RON to be safe - my mechanic had done this mod before - no problems reported by other owners.

awesome motor but i have no real comparison to offer re different cams etc.

hoping its going to last.....

nathan

Although there seems to be a bit of confusion over what the actual compression ratio is. Rest assured that the 2.2 E pistons will give a lower CR than the 2.2 S pistons when used with the 2.4 crank.

If you already have the 2.2S pistons then I would keep them. You can always lower the CR with shims under the cylinders if you need to.