I'm looking what CR should be for 400 - 450bhp. Standard 4x4 pistons .25 or bore valve cut outs. Bd10 exhaust and bd14 inlet

 

Are you asking what CR people recommend or what CR your engine is right now?

 

What it should be

 

What head you have?

 

2wd head

 

Around 7.8 if not skimmed to much

 

I am not sure if there is an exact science to work it out but 7.4 to 7.8 seems to be what most big power engines have. Are you building the engine yourself or having it done by a Cosworth specialist?

 

i think that is well to low ,at least standard now seems to be the way forward

 

Maybe things have changed but most big power Cosworth YB turbo engines have low comp. High comp used to be more for N/a engines. What reason is there for having the higher comp ratio?

 

You need to speak to Mark Shead

 

i think low comp was a long time ago,high comp less lag better off boost driving etc just a nicer car all round as james says mark shead has been running higher comp for a while and from what people say his engines seem to be the best now

 

I would go 9/1 with good ecu.

 

Maybe 10 years ago but mines at 8.6 : 1 & is the modern way.