Increaseing Compression

[Ultrasonic2]

Can i just take my head off and mill it down abit ( i will get this done professionally ) to increase compression, to say 12:1....My question is .....

Will the stock ECU still beable to run the car with it's new compression

Is there enough clearance between the top of the cylinders and the top of the head ( or will anything else hit )

Any other reasons why it wont work ?

[G-Forces]

Are you talking about a G20?

I'll assume you are since it's in the G20 forum.

Not a good idea to do this to increase compression. The ECU will not handle increased compression past 10:1 I think. 12:1 will definatly need a reprogrammed ECU. milling the head will throw off your cam timing. You'll need to get cam gears and reindex your cams. If you're going to take off the head just get the proper pistons for your application.

[Ultrasonic2]

i must admit 12:1 is a little optomistic....... does anyone know why the ECU wont let it run with more than 10:1 .compression ..... i would have thought...it wouldn't really matter besides changing the ignition timing ( good point about the cam timing though ).......

as for changing the pistons the car isn't really worth spending that kind of money on it .

[T4 Primera]

Be careful about valve to piston clearances as well.

[P10DET]

Originally posted by Ultrasonic2
i must admit 12:1 is a little optomistic....... does anyone know why the ECU wont let it run with more than 10:1 .compression ..... i would have thought...it wouldn't really matter besides changing the ignition timing ( good point about the cam timing though ).......

as for changing the pistons the car isn't really worth spending that kind of money on it .

Pipe dream.

Just dialing back the base timing is monkey tuning. In fact, you would have to pull so much timing out to deal with the most difficult parts of the map that you would probably create problems elsewhere that are impossible to overcome.

The map for a 11:1 CR engine is very similar to a turbo map. The ignition timing is manipulated throughout the map. It's so critical that my enigne and another like it would detonate slightly during the summer, and that is with the remapped ECU.

As Sandy said, you will likely run into valve clearance problems as well. I don't think it's physically possible to remove enough material to raise the CR that much without interference.

My 11:1 engine used both flat-topped pistons and reshaped combustion chambers that lowered the chamber volume from 46cc to 43cc. You could get more CR only by using domed pistons, but the chamber would need to be shaped rather differently.