eds240z Posted March 24, 2010 Share Posted March 24, 2010 I basically didnt do my homework!! I just rebuilt my engine(f54 block p79 head) and it worked great! I'm currently running it with triples, headers & ignition. I recently came across a P90 head thinking i would create more hp, but ended up slower then my last setup. I had the head rebuilt, matched ported & polished the intake & exhaust. I was thinking it was a installation error so i did a leak down test & compression test. I found no leaks but I only had 120 psi across the board!! I have a F54 block with stock flat top pistons. I'm pretty sure i'm running the wrong setup. what head should i use to get the most power? sorry , i forgot to mention i'm running a stage 3 cam from motorsports. I was looking around and i saw E88 & E31. Is this correct? Quote Link to comment Share on other sites More sharing options...
DAW Posted March 24, 2010 Share Posted March 24, 2010 The P90 is a turbo head. By replacing your P79 with a P90 (more cc in combustion chamber) you lowered your compression ratio and reduced the power of your engine. At this point, consider turbocharging the setup you now have. You will have increased static c.r. as compared to the OEM turbo (P90) spec engine, but if you intercool and limit boost, and run Knock sensor, it will be a nice combination. (and it has a nice squish factor re the flat tops and chambered P90) DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted March 24, 2010 Share Posted March 24, 2010 I basically didnt do my homework!! I just rebuilt my engine(f54 block p79 head) and it worked great! I'm currently running it with triples, headers & ignition. I recently came across a P90 head thinking i would create more hp, but ended up slower then my last setup. I had the head rebuilt, matched ported & polished the intake & exhaust. I was thinking it was a installation error so i did a leak down test & compression test. I found no leaks but I only had 120 psi across the board!! I have a F54 block with stock flat top pistons. I'm pretty sure i'm running the wrong setup. what head should i use to get the most power? sorry , i forgot to mention i'm running a stage 3 cam from motorsports. I was looking around and i saw E88 & E31. Is this correct? Quote Link to comment Share on other sites More sharing options...
DAW Posted March 24, 2010 Share Posted March 24, 2010 Or, since you have some $$ invested in your triples/header/etc., you could use an N42 head or a late E88 head and have 10:1 c.r. which will definitely wake up the power...but these heads have a tendency to lead to detonation even with a reasonable amount of spark timing advance (and you'll want to run a bigger cam too). The closed chambered heads like the P79 and P90 run with flat top pistons tend to circumvent these detonation tendencies. But all things considered, either run pop-up pistons/P90/triples; or flat-tops/P90/turbo. The turbo is cheaper, sell your triples and just find a stock 280ZXT and take the whole turbo manifold/turbo/injectors/intake/ECU/distributor and intercool it on your P79 shortblock, and you'll be happy with the result. DAW Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted March 24, 2010 Share Posted March 24, 2010 The P90 is a turbo head. By replacing your P79 with a P90 (more cc in combustion chamber) you lowered your compression ratio and reduced the power of your engine. At this point, consider turbocharging the setup you now have. You will have increased static c.r. as compared to the OEM turbo (P90) spec engine, but if you intercool and limit boost, and run Knock sensor, it will be a nice combination. (and it has a nice squish factor re the flat tops and chambered P90) DAW UMMM, the P-79 and the P-90 have identical combustion chambers Quote Link to comment Share on other sites More sharing options...
z-ya Posted March 31, 2010 Share Posted March 31, 2010 The P90 is a turbo head. By replacing your P79 with a P90 (more cc in combustion chamber) you lowered your compression ratio and reduced the power of your engine. At this point, consider turbocharging the setup you now have. You will have increased static c.r. as compared to the OEM turbo (P90) spec engine, but if you intercool and limit boost, and run Knock sensor, it will be a nice combination. (and it has a nice squish factor re the flat tops and chambered P90) DAW The only difference between the P90 and P79 is the exhaust port shape. Do you have a round port header? If so, it might explain why you are seeing less power. The P90 has square exhaust ports. Combustion chambers are the same BTW. Pete Quote Link to comment Share on other sites More sharing options...
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