Increasing Compression on a 3.2.

[David W]

I would like to increase the compression of my US 3.2. The engine is apart and I have a nice set of US P/C (Malhe). I was thinking of cutting the heads and chain housings by 1mm. Ollies’s charges about $200 for this. I plan to use the stock DME and don’t want to use JE’s. Does any one know what the CR increase will be (done this)? I would like to get close to Euro (10:3) specs?

Thanks, David

[RickM]

Wouldn't you be required to use higher octane gas to prevent detonation...and have the DME matched to the compression change?

[David W]

I have several friends using euro P/C (10.3) here in Alabama (93 octane avail.) with no problems. I think it is important to retain the factory piston top as it makes a difference in flame front propagation and "hot spots". There is a lot of thought put in to piston shape. The factory dome acts as a "squish chamber" to push the gases toward the spark plug.

[ChrisBennet]

As much as cheap horsepower appeals to me, I probably wouldn't do it. The factory stated compression #'s are higher than the measured ones so a Euro "10.3:1" really measures out to something like 9.8:1. 9.8:1 is about the limit on pump gas (single plug).
If I wanted to raise the compression cheaply, I would lengthen the rods.
First I would measure the current deck height and if the deck height was 1mm or less I'd scrap the idea. If I had more than 1mm I'd consider reducing the deck height.
Second I would measure everything and calculate the true compression and how much deck height I could remove before compression got to 9.8:1.
Third I would simulate removing .25mm by removing the base gaskets (.25mm thick) and assembling the motor with some solder or putty on top of the pistons (I use Silly Putty) to determine the actual clearances. That's just what I would do.
Disclaimer: I consider myself a "student" in these matters. Hopefully a "teacher" will weigh in.
-Chris