My Question is, if you increase the compression ratio of an engine (IE change pistons or skimm block etc) how will that affect the mixture if everything else remains as standard?

+EG: if you had an engine running on webers or standard EFi if you increase Compression ratio how will that affect the mixture?

Hi Mate

I would think you will need a richer mixture. The higher the compression ratio, the more it is likely to pink so you will need a richer mixture or a higher octane fuel and probably you will need to change the timing too.

Cheers

Mark

Possibly. It depends a lot on the engine and set-up. Theoretically no, as the new charge is drawn in at the same AFR, and all the old charge is expelled.
I doubt you'd notice it if the AFR did change.

Edit:are you asking if the AFR would need to be changed, or if with the same fueling the AFR will change?

[Edited on 18/4/10 by brianthemagical]

Yes, my question is would it require re-jetting or re-mapping... and if so would it required to be leaned off or enrichened?

You'd be able to get away without a re-map, depending on what the CR's are. Ignition timing would possibly be OK, but there's a chance it may det, depening on the engine. You'll probably find gains from a re-map though, and why go to the trouble of changing the CR without a re-map.

Basically I have rebuilt a toyota 3s-gte engine. I have used the same exact parts (IE no upgrades) but its running incredibly rich under heavy load & boost IE 10:1 AFR, I had skimmed the block and the head plus pocketed the pistons to suit CR. I obviously have done something wrong but cannot figure what

What kind of managment/fueling does it use?
What kind of AFR's was before the rebuild?

Standard Management using an airflow meter not map. I used to have 11.7:1 now its way below 10:1 under boost... way to rich.