Advice Sought... 2.2 E Pistons vs. 2.4 S pistons with E cams?

[M491]

Hello. I am looking for the advice of the experts, please. I am having a stock 1972 911T 2.4 MFI engine professionally rebuilt. The MFI I'll be using is straight off of a perfectly running 2.2 E engine. The cams are new E cams. The quandry is, which pistons and cylinders should I use? I want the engine to be the strongest and fun, but street-usable as possible. I have two good sets. One set is 2.4 S pistons and cylinders, and the others are 2.2 E pistons and cylinders. I know the E pistons will offer higher compression, but I think the 2.4 pistons were also really good, right? I just don't know which to choose! The heads are the standard small valve 2.2/2.4 MFI heads with stock ports. I would so much appreciate your kind advice on this topic! Thanks in advance!

[Richard]

My 2.4L '73S has stock 8.5:1 compression pistons. It runs great and is fairly strong. However, higher compression as long as you have the gas octane to run it, is free horsepower. As I recall the 2.2 E pistons had a compression ratio of around 9.1:1 on the short stroke 2.2 motor. When installed on a long stroke motor like your 2.4 the compression ratio is bumped about one half a point to around 9.6:1. The cylinder head design on the 911 motor seems to be somewhat forgiving on compression so my guess is that you shouldn't have any trouble running 2.2E pistons on your long stroke motor even with todays bad gas as long as you run premium. But since you are having this done professionally I'd talk with your mechanic about it. You will want him to stand behind the engine rebuild and he may have a preference on which way to go.
Rich

[orange911]

I had this same concern, but I had 2.2S pistons (used, within spec). I was concerned enough that I opted to sell my 2.2 P&C and bought a set of 2.7RS Euro P&C (used, within spec) with a lot of change left over.

Added compression is more stress over the life of the motor. I probably would not put enough miles on mine to matter. But if the 2.2S was so great with higher compression, why didn't the RS have it? My guess, too much power for the case.

I also did not want to take the chance of building this motor and having it beg for octane. Twin plugging is a great option and will eliminate all concerns, but it was too expensive for me. I am putting my leftover change into opening up the TB and stacks and getting a new space cam installed into an MFI that needs rebuilding anyway.