Kevin Baker

I have an "extra" short block. It is from an early n/a. I know that there is a coating on the cylinders, but is it possible to overbore say to 3.0 liters, and is there a source for pistons? I have thought about the later 968 pistons, but would they work with a standard n/a head? Not too sure about when I'd do this, or why. Just kind of exploring at this point.

StoogeMoe

I'm no engine expert, yet, but I'd say you can't do it. The 3.0 liter engine used 104mm pistons and a longer stroke crank. The original 2.5 used 100mm pistons. They changed the cylinder spacing to accomodate the 104 pistons, therefore you couldn't use that longer stroke crank in a 2.5. Plus, there's no way I can see you getting 4mm out of those bores.

The cylinders aren't coated, but they are processed with special techniques to have the aluminum removed so the silicon stands out and make the cylinder harder. The pistons are iron coated to handle this extra hardness.

I could use a short block. Want to sell it? Too bad you're pretty far away.
____________________________________
1986 944 NA - Guards Red - 81k miles
1984 911 Carrera Coupe - Guards Red (gone, but not forgotten)
"If you're not living on the edge, you're not living"

pearldrum944

I thought there would be more of a difference in piston size than 4mm, cool.

Tom Carson

much of what you are curious about is probably answered here:
https://rennlist.com/forums/944-turbo-and-turbo-s-forum/181181-new-sleeves-mid-are-finaly-here.html

doubtful 4 valve pistons would make sense unless you are considering getting machine shop work done to them

pearldrum944

Very cool, I need to read the turbo forum more....

Kevin Baker

Ah, that's a bit more work, modification, and money than I was thinking. I guess a better question would be. Is there a way to hone down the "ridge" and fit new pistons and rings?

Tom Carson

good info in this thread:

https://rennlist.com/forums/944-turbo-and-turbo-s-forum/177236-stock-piston-ring-material-or-ring-material-for-use-with-alusil-blocks-x-post.html

do you actually have a 'ridge' that needs to be honed??

M758

The bore spaceing did not change. You can sleeve the currnet block to get 104 mm bores. The 3.0L cranks can be obtained and used in 2.5 block. That is how 951's get 2.8L motors

It will take a fair bit of machine work, but shops have done it and even build 3.2L motors.