James_R 3 Posted April 9, 2006 I've searched but can't find the answer, how much needed to be removed from a std Mi head to get the CR up to 10.8:1? I'm just about to get my hed back from being flowed and would rather it got skimmed there before it gets hot tanked to clear all the swarf out, rather than having to tank it twice. Thank you for any help James Share this post Link to post Share on other sites
petert 588 Posted April 9, 2006 You don't. Skim the block and liners 0.38mm. Share this post Link to post Share on other sites
cybernck 402 1 Cars Posted April 10, 2006 and what about increasing it from 9.7:1 to 10.4:1, peter? or is it better to just fit "high" compression pistons? Share this post Link to post Share on other sites
petert 588 Posted April 10, 2006 Pistons are good if you can find them, but they're still sitting 0.38mm down the bore. It's cheaper to skim the block and liners if you're happy with a cast piston and you get a better result. They run much better with zero deck height. Mind you piston to valve clearances become an issue. Without looking at my notes, you can have up to 0.110" lift at TDC if you're happy with 0.070" piston/valve clearance on the intake. That allows for another 0.010" at 6 deg. ATDC. Exhaust isn't an issue as you'd use the standard cam with that sort of spec. anyway. To take a 9.7:1 XU9J4Z to 10.8:1 skim 1.30mm. Share this post Link to post Share on other sites
James_R 3 Posted April 10, 2006 That's a fair amount to take off then, didn't realise it was that bad, I'm planning to fit the catcam inlet cam in the near future, would this cause valve clearance issues with the head skimmed this much? is 10.8:1 the best recommended CR for a fairly standard Mi then? thank you for you help Share this post Link to post Share on other sites
petert 588 Posted April 10, 2006 Pick a cam with less than 0.110" @ TDC, unless you want to machine the pockets. 10.8:1 is about the best you can do with the standard flat top piston. Share this post Link to post Share on other sites
Ahl 4 Posted April 10, 2006 Peter, are you remembering that we don't get the 9.7:1 XU9J4Z in the UK, only the higher compression 160hp engine. Does this make a difference to your advice? Share this post Link to post Share on other sites
petert 588 Posted April 10, 2006 As I said, skim 0.38mm from an XU9J4, or 1.3mm from an XU9J4Z, to achieve 10.8:1. All the other info is then the same, as the piston is now flush with the top of the liner at TDC. Share this post Link to post Share on other sites
Ahl 4 Posted April 10, 2006 Ah I understand now. Sorry, I didn't read the thread properly. Share this post Link to post Share on other sites
