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Discussion Starter #1
im going to swap an F54 block into my 73 240.. im keeping my su's and i am going to get the block bored slightly, add a mild-medium cam, port matched header and intake etc..i will be racing the car once in a while but i want a mean street machine too.. the block i have has a P79 head on it.. should i work that head and keep it or buy a P90 for 150 or so and work that one? thanks for the advice
 

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P79 is pain because the sleeved exhuast port. I got one with the sleeves taking out. the exhuast port is huge! bigger than intake which isn't good. I did get good power out from it.
 

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so what should i do here keep it or dump it? how much more power is the P90 going to give me? 150 dollars worth? also if i was to mod the P79 to all **** like bryan littles webpage. would it produce more than the P90 modded?
 

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everything is same except better flow intake and square exhuast ports. P79 can be ported to get same amount of intake flow. Exhuast, round port are better because they give faster air flow but with the sleeve off it may be too big and slow the air flow in the lower rpm like my P79. It was streetable but power band didn't come in 'til 2000rpm. Benefit to square port is MSA 6 in 1 header fits without mods. P90 would be a better choice because it would be easier to get power. $150 may be worth it considering the cost it would cost to have the P79 ported to get some amount of power.
 

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there isn't a huge difference between the two heads in performance. You will definetly get more performance out of the P79 if you raise the compression as described on Blittle's site (that's assuming you don't raise the compression on th P90). If you are going to build the P90, I suggest doing it the conventional way, use the pistons to raise compression. The P90 is a little more rare and probably worth the few extra hundred dollars for domed pistons. I am currently running the P79/F54 combination with the head shaved in the manner described on his site. I am running the FI and some additional mods. I am NOT dissapointed.

You can check out my car here.

http://zdriver.com/rides/detailride.php?cat=1&relIdx=10&vehId=197
 

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one other option is to use one of the earlier heads, n42, n47, e88, e31, with the flat top pistons you already have in your F54 block. these will give you as good to better performance (compression ratio) without having to spend the extra bucks on shaving the head, new valves etc. if you want to stick to either a P79 or P90, use the P79 you have now and do the mod. P90 is not worth the extra $150 for what you are doing, IMO. spend the $150 on your cam or headers.
 

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Discussion Starter #8
im thinking i wont buy a new head just yet.. i also have a E88 from my 73 240 i can use.. i think that has square exhaust ports
 

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If you are going to use the SUs then definetly use the E88. You will have about the same compression, actually a little more with the E88, as if you shaved the P79 or P90. The only difference between E88 and shaved P79/P90 would be the compression chamber shape. It should work well with the E88 though.
 

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If you read my post again you will notice I said he would make more power with the P79 if it was shaved and the P90 was not. I guess I didn't state that clearly enough, I went on to suggest using higher compression pistons instead of shaving the P90. Because of the P90 is a little more rare than a P79 it's probably worth spending the extra money on the appropriate pistons to raise compression as opposed to shaving it. You were correct to say that the P90 should make more power with the same setup other wise. Sorry, for the mix up.
 
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