Ian928

Hi!

I recently posted a question about using old (80 euro 16V) heads on a 85 block. The answer was yes, this would be a very good set-up. Also, someone mentioned that using a S4 block with 16V heads would yield too low compression ratio.

My question is this: How low would the compresion ratio be? If it was around 8,5-9:1, I would think that was a perfect set up for turbos or supercharging? Am I right? A lower static compression ratio should make it possible to use higher boost before detonation occurs, thus putting more air into the cylinders and producing more power? I think the 944 turbo had 8:1 compression and 8V head. If I just created a double 944 angine with the same compression ratio adn boost, this surely should be dependable and powerful?

Any comments, anyone?

chris928

Typically lower compression ratios yield better results with supercharging, but there are a lot of factors here. Are you using an intercooler (sometimes called aftercooler with a supercharger)? This makes a big difference. Also, if you are putting heads on an engine, you can dial in the compression ratio somewhat at that time by use of different thickness gaskets and machining of the combustion chamber in the heads. Also piston selection changes things if you're getting into the bottom end.

You need to take a really good overall look at your approach to this. There are so many factors to consider.

If you're going to supercharge, you probably don't need to mix-&-match engine components as the 928 is very supercharger-ready as it is.