kz vs J compression decreaase

i torched the pistons in my bike tonight, too much abuse, too hot, and maby not enough(or too much) e-85, it still runs, but i obviously need change.

anyways i want to sell my harley (i know:blush:) to build a motor from scratch, and i was curious what the drop of compression would be if one stuck a J head on a pre 80 kz1000 engine.

ape does not show any bigblock piston sizes for low compression turbo use, and i was hoping an 10.25kz would equal an 8ish J motor compression.


any help would be gratefull

and has anyone here had their crank welded and their tranny backcut and howmuch did it run you

-2 points in a post the other day

APE Jay ought to put me on the payroll

The J model / '81-'82 GPZ1100 cylinder head has a larger combustion chamber than the early style head. When these heads are used on the early style motor, a compression ratio drop of about 2 full points can be expected.

www.aperaceparts.com/tech/techkz1000.html


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I know it is possible, but is it worth it... shave the Jmodel head to retain compression.

I asked a similar question yesterday as to why use the Jmodel head. Someone said it is cheaper... so therefore shaving the head to retain compression probably isn't a viable solution.

the only reason i want to know this is that there are no low compression pistons listed for the J engine, and i want my next engine to be a low compression big block motor, expecting a turbo to be added to the bike in a year or two.

Using a J model head with high compress (10s) will get you almost standard compression in the 8s. This provide a really lazy response with carbs, but perfect for forced induction.