Originally Posted by greglewis
To me, this is where it's getting very interesting for an armchair engineer/noob like me. It's been established that the bore will remain the same (no cylinder change). I think it also means no change to cylinder barrel length, and the piston top comes to the top of the cylinder at the top of the stroke - it sounds like the stroke is the only variable factor.
1) correct me if I'm wrong
2) explain the considerations between changing the connecting rod length and/or changing the length between the crank pin and the centerline of the crank.
Our initial donor engine is an 08 motor,so 654cc.This is 102mm bore x 80mm stroke.
Our initial attempt is to keep the std bore,and gudgeon(wrist) pin height,then move the crankpin 12,5mm nearer to centre of crank,giving the 25mm reduction in stroke needed to achieve 102 x 55= 450cc
But,because of the reduction of swept volume,we have to "lose"approximately 20cc from the head volume to maintain the same compression.That will be the difficult bit,as we will be running the rally cam,so there will have to be quite a pronounced dome on the piston to up the compression,but still miss the valves.
Onward & upwards..........