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if you have dished pistons n-42 ok i am using a n-42 w/flattop pistons and my compresion is a lil high i had a 50 thousandths shaved p-79 before that had me aroung 9.5 to 1 and i should have kept it i swithched to have the square ports but the head shop flow benched both and said even w/the steel ex. port liners that the p-79 would flow way bettter ,hind sight is 20/20 if you have dished pistons a n-47 off a ealy maxima has the higher compresion of the n-42 with the better flowing ports and quench chambers design of the p-79 this info was confirmed by ron of nissan motorsports also a nother idea is brain littles to shave a 9=p-79 80thou and use n-47 valves and shim the towers to get 10-to 1 the expense of the shaving and tower shims out way the hunting for a max n-47 though ron said you would have to be in the 7-750 hp range before you would truley benifit from the square port head even though my compression is higher now i know my shaved p-79 flowed better i can feel it so if you can find a max n-47 i think that would be the E-TICKET

hope this helps
have fun or its all in vaine
 

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neither of these heads are going to perform any differently on a stock L28 (with dished pistons, right?) even with flattop pistons there will be little if any difference. use whichever head is in better shape, that should be the determining factor in your case.
 

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Discussion Starter · #4 ·
OK, it;s just that I have both heads. One has larger valves, right? One has more compression, right? Assuming similar ports, there is no advantage one way or another?
 
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