Originally Posted by ktmmitch
Bloody hell Lyndon,it's a good job I'm on holiday this week so I have time to answer all those questions!!!
In response,here is the best I can explain .........
1.Cosworth understood that our brief was to try and keep the cylinder head standard,so that we can hopefully supply a customer 450 kit,which will consist of a short-stroke crank,and new piston,therefore making the kit as simple(and cheap) as possible.To this end,we realise we have compromised the gas flow,as they had to design such a high intruder into the combustion chamber,in order to get the compression back to standard,due to the fact we are only now sweeping 450cc instead of 654cc into the same head.This wont become apparent until we build and run the motor,but we will have to cross that bridge when we come to it.
2.Initially we will try the std cam & 690 rally cam,but have offers of cam design help from outside if we need it.
3.We annealed the piston after welding and will stress-relieve it after machining,it did distort slightly,as the gudgeon pin was very tight going in,so we reamed it back to 20mm diameter.It is something we will have to live with for the prototype engine.
4.Cosworth engineers did suggest the reduction in valve & port size to get more efficiency,but again, we want to keep the head standard, for simplicity.
5.The new production 450ccCosworth piston will be slightly heavier than the OEM version.The other 2 versions(stock comp & hi-comp 690cc) will be OEM weight.
Like you say,we are on a journey,not quite sure of the result,but we are definitely going to give it our best shot at making a "clubman" Dakar-spec 450 Rally bike, that is affordable and uber-reliable.We realised that from Day 1 it would never have 450RR power,but that is what we are prepared to swap for reliability and expense.
It will be great to get it on the road and trail ride it soon,come down and try it out.