screamin_mimi Posted August 3, 2011 Report Share Posted August 3, 2011 Does anyone know what the comparison in compression would be --- If I have bored cylinders 10 over with a prodesign cool head using 18cc domes.... and getting a compression of 160. What would be the comparison of this to Milling a stock head?? .010 / .020 / .030 over???? Thanks!!! Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted August 3, 2011 Report Share Posted August 3, 2011 160 with 18's whats your elevation ? 4000 above or something ? at sea level, .030" off a stock head would put you around 150-160, if your that high up, you will have you machine too much off the stock head, and youll have to get the chamber's and squish bands reshaped. Quote Link to comment Share on other sites More sharing options...
screamin_mimi Posted August 3, 2011 Author Report Share Posted August 3, 2011 In Michigan ... at about 800 ft asl Quote Link to comment Share on other sites More sharing options...
coryv4 Posted August 3, 2011 Report Share Posted August 3, 2011 In Michigan ... at about 800 ft asl that cant be right get another compression tester i am running 23cc domes and i have 145psi and i am also in michigan at 700ft Quote Link to comment Share on other sites More sharing options...
mopar1rules Posted August 3, 2011 Report Share Posted August 3, 2011 Cranking compression values also depend on how high the exhaust port is. Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted August 3, 2011 Report Share Posted August 3, 2011 Cranking compression values also depend on how high the exhaust port is. exactly......say if you had a port job that raised your exhaust port height and put your stock head back on you would notice a lower compression number than before you changed the port heigth. do you have it ported? Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted August 4, 2011 Report Share Posted August 4, 2011 yeh youl notice a slight decrease in static compression when ported ( depends on porting too), but it makes up for it in flow in the upper rpm. (dynamic compression) cory with your 421, due the the bigger size motor, the dome cc is increased as with the engine, so to get the same cranking compression as a 350 you need bigger domes, in my 421 i was running 20cc domes and pushing 170+psi now with 24cc's it down to around 135-140psi. on the stock stroke/bore 20's were pushing 155-160psi cranking compression. try another gauge S/mini. Quote Link to comment Share on other sites More sharing options...
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