J4R Bottom With J4Rs Top?

[Richie-Van-GTi 71 2 Cars]

Ive done a few searches and get conflicting info. Is the j4r lower compression than the rs? Is this due to head or bottom end? I know pistons are different but cranks the same.

I ask as I have a heavily skimmed rs head which I am considering building onto a good R bottom end as a spare engine then putting a normal height head onto my RS bottom end as my main engine.

The skimmed head had had .5 together so just beyond max skim of .4 however the valves have been cut .5 further in to recreate the celearance at TDC and springs shimmed up. I Also have a +.2 gasket to use so thinking with the R bottom end may be very similar CR to RS engine if the two are different?

[Miles 331 1 Cars]

All the iron blocks are the same, it's in the finishing where they get to a engine type, 8v and 16v this applies to

[welshpug 1,657]

max skim is .2 not .4!

 

difference is in the pistons.

Edited September 10, 2015 by welshpug

[Richie-Van-GTi 71 2 Cars]

Well its .1 beyond the max skim, i thought it was .4 but I know definatley .1 over.

Any idea on measurements for CR to do a rough estimate on how similar the 2 builds would be?

[petert 586]

A friend of mine, whom is a race car builder by trade, measured up a standard, original RS recently and got only 10.4:1. So whilst the pistons may be different I don't think the CR is necessarily so.

 

Here's some of his work:

 

http://www.aussiefrogs.com/forum/restoration-projects/116014-cam-pats-205-race-car.html