Porsche94483

somebody could help me; I have a 924s 2.5 cc M44/07 150 cs engine, and I want to change the pistons of a M44/01 2.5 163 cs, for more compression. The pistons have 1 written on them and the others have 1. Could I change them? Are the measurements compatible? thanks help

walfreyydo

I think the number on the piston is the bore tolerance group and your block should also have a number stamped on it (likely a 1). I think you can run the different pistons but they need to be from the same tolerance group. Maybe others may have more info.

https://924s944.com/2019/01/28/engin...-and-hp-oh-my/

curtisr

Have you considered shaving the cylinder head for starters?

walfreyydo

Wont shaving the head cause issues with timing, due to the shortening of the belt distance?

curtisr

Thanks to the tensioner, TB length won't be an issue. Vintage racing (VARAC) allows for the removal of 1/10th of an inch as a normal part of head maintenance. More than that and you've given the stock motor an unfair advantage.

Porsche94483

Shaving the stock won't recover much. To recover that size how much would I have to shave?

curtisr

Uncorroborated (by me):

For 10.8:1 = 0.53 mm or 21 thousands of an inch. For 11.1:1 = 0.77 mm or 30 thou.

Source: https://rennlist.com/forums/924-931-...ion-ratio.html Post #10