how much to skim to raise cr to around 11:1?
Turbo Mini Forums

hi all, im looking to modify my mpi cooper. will be doing a few bits and pieces to the engine. have a spare head, which i will recondition, and port and polish.

i know that the cooper works conversion ran around 10:1 cr. am hoping to raise my head (with standard size valves ) to around 11:1.

how much do i need to get skimmed off? also, at what point will 1.5 ratio rockers make the valves hit the pistion tops?

cheers

I believe Veragrd once said that every 12 thou resulted in 1cc. This was in relation to a 12G202 if I remember correctly. It's a good starting point though. You could use this as a guideline and take a bit too much off the head. Then grind out the chambers a little to get them where you want

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

Hi,
How are you going to correct the ignition timing when you raise the compression?
Cheers,
Gavin :)

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how high can the compression be raised on standard timing?cheers

Depends on your fuel octane rating. You would also need to know what CR it's running at now. Off hand, 11:1 sounds like alot for the ignition map of a standard MPI

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse