So if i was running 1mm oversize pistions on a stock hear gasket with heads that have had 1mm taken off them what would it C/R be? Is it worth redoing th heads?
Taking a good guess and saying you have now got a combustion chamber 5cc less than standard you will have a 9.6:1 cr approx. Now the max allowable limit to be machined off the heads and block combined is 0.2mm, you have machined 1mm of the heads alone, has the block been machined? You are going to need to be spot on with the tune, but otherwise you will not see any issues.
He has increased the swept volume 10cc and reduced clearanced volume 5cc due to a 1mm over bore and 1mm deck. That is a 2.5% increase in bore sized and a 10% reduction in chamber volume. Chamber volume has the largest effect on compression ratio more than any other single component, this is why it is very important to know how much is the max limit, in the vg30 it is very little as it is in most 4 valve turbo engines. This is a total gain of 12.5% compression pressure. Note all figures rounded for easy math.
Your a champ. Yeah the mistakes we make. I guess i can live with 9.6 Although its nothing a set of cams couldnt fix Now if only i could find myself a set of leader gears.
interesting. Looks like my engine had around 9:1 then 40 thou oversize pistons heads decked 20 thou at least and block had some off too. was wondering why it was responsive with good tyre shredding torque. (considering the big highflows)
With the 1.6mm cometic im running with very little lag. I think i was making 6 or so psi at 2500. I cant remember. Should be interesting with even higher compression. and leader gears, if i can get some.
keep your eyes on the 300zxclub forum ,they pop up every now and then . thats where I got mine ...private sale only cost me $700au delivered
