ford40

does any one out their know if there is any advantage fitting 302 heads to a 351 block, would it increase compression or restrict breathing ?

GT-P 738

Yes it will increase the compression ratio and if setup correctly give good peformance gains.

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northey

There's a few good posts on here about that - just check them out
cheers

pinkbits

thats the setup ive got at moment with 4v exhaust valve
with the pistons ive got its a bit above 11 to 1 and it only had pinging when it started as the tank had crap fuel in it , now i run high octane and no troubles , never dynoed so cant give you figures

soverign

the cc heads will increase static compression,cylinder pressure,and dynamic or effective compression...this is probably the most important aspect of this swap that you have to watch,as far as compression is concerned...
dynamic compression is dictated,most importantly by the intake valve closing position in relation to the position of the piston going up the bore on the compression stroke...
if you have an early intake closing valve,with say an oc head,you might not have a problem with over compressing the mixture...but now increase the STATIC compression,coupled with the early closing valve,and you can quite easily over compress the mixture,inducing detonation...especially in the lower rpm band...this senareo coupled with a heavy car,high diff gears and poor booster signal,is a great recipe for detonation and mobs more heat...

if the car has a higher convertor and lower diff gears,the problem is not as bad,as these will help the car pull through the rpm quicker,and not let the engine linger longer at lower rpm where the airspeed through the ports is slower...

get the combo right,and you get the advantage of the faster mixture burn that the cc head has,makes more fuel efficient power...you can use less timing,less negative torque...

the oc head has a larger chamber,and the flame front has a further distance to burn,hence the need for more ignition timing...more negative torque...

as far as the restrictive breathing is concerned,yes at lower valve lifts,but once the valve gets past .450" lift this effect drops off...that is why backcut valves work well on cc heads...
the beauty of the cc head,as far as the chamber is concerned,is that you have material there,so you can open it up slightly,and get the desired shape for the valve angles,to help flow at low and high valve lifts...