Head Changes/Compression

[ecp48]

javascript:smilie(':stupid:')

I have noted a number of comments on the site about not raising the compression beyond 9.0:1 due to fuel considerations.

In the past, with American V8s, the rule of thumb was, that you could raise the CR by one point if using an aluminum head. Why doesn't that work with a Z head (L-6)?

Further, does anyone have a rule of thumb for how much the compression goes up on a N42 or 79 head per thirty thousands (.030) cut/milled off head surface?

I read on another site, that an eighty thousands cut on a P99 would raise it to appx. 10.0:1, but this is the 81-83 head with the larger combustion chamber/raised deck (8.3:1 to begin with).

Also, when using a high lift/longer duration cam on the L6, I am told you can go with a higher compression.

My last experience with Zs was a 1975 280Z Coupe, only Mod was a header. (A big throat was beyond my budget at the time. Starving Student with a Formula V habit. Amazing how far the GI bill would stretch!) (2nd in Class, beat by a 240Z in the 1980 Bay Bottom Crawl.)

Anyone have any thoughts on the compression issue?

[beandip]

:classic: I recently bought a 54 flat top engine with a 79 head milled 30k and was told that it was at 9 to 1 . The mechanic I bought the engine from , this was his personal engine, said that it was about 9.2 to 1 . With out measureing the volume of the head and cylinder at tdc , you cannot be sure. But from what I have found out asking this same question figure about 9 to 1 with 30 off the p-79 is what you will have.:classic: hope this helps

[ecp48]

Thanks,

It gives me a statting point. I think I'm going to have to invest in a burette.

Ed Palmer