Guest pintoz Posted January 6, 2004 Share Posted January 6, 2004 While waiting for my T3/TO4E to come in, I now have to make a decision. I've spent a couple of hours now trying to search for a suggestion as to which head to use. I have a p90a hydraulic head on my 83 zxt or a p79 from my 81 zx n/a. I would prefer to use the p79 because it is a solid lifter head, but is it better to have a 'turbo' head on a turbo motor? Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 6, 2004 Share Posted January 6, 2004 isnt the p79 a round port head? if so P90a P90a may have the HLAs, but it still has the preferred swirl combustion chamber. A p90a head in good shape is worth running worth the turbo ap, even if you run one in the meanwhile before you find a solid p90. Quote Link to comment Share on other sites More sharing options...
Guest Boyd Posted January 6, 2004 Share Posted January 6, 2004 I just installed a P90 with mechanical lifters. This seems to be the consensus of the best head to use. Reynolds Quote Link to comment Share on other sites More sharing options...
David K Posted January 6, 2004 Share Posted January 6, 2004 My p90a build is coming along slowly, but progressing none the less. Ive rebuilt my hydraulic lifters, replaced the springs inside with new ones, and now im getting started on the head. I would go p90a, because the valve guides are stainless steel and last a lot longer, if not forever. If you are concerned, check out this thread to see what you are getting into with hyrdaulic lifters. http://hybridz.org/phpBB2/viewtopic.php?t=26904&highlight=hydraulic+lifters The p90a is truely a great head, and the last inline L series head that Nissan marketed. I have one in perfect condition. People say you cannot run a performance cam on these heads due to the hydraulic lifters, but i am certain that it is possible, after researching and spending time with the head and its components. Good luck. Quote Link to comment Share on other sites More sharing options...
Guest szlash280z Posted January 6, 2004 Share Posted January 6, 2004 hey ghost, the P90A has springs inside the lifters? I never took mine apart so I don't know. do they have a lot of tension to them? where did you get new ones? Quote Link to comment Share on other sites More sharing options...
David K Posted January 6, 2004 Share Posted January 6, 2004 hey ghost, the P90A has springs inside the lifters? I never took mine apart so I don't know. do they have a lot of tension to them? where did you get new ones? I just went over to a hardware store and got the next up strength spring. The stock springs are about 1/4 long, so you need to keep it about that length, no shorter. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted January 6, 2004 Share Posted January 6, 2004 isnt the p79 a round port head?if so P90a P90a may have the HLAs' date=' but it still has the preferred swirl combustion chamber. A p90a head in good shape is worth running worth the turbo ap, even if you run one in the meanwhile before you find a solid p90.[/quote'] Uh, P79 has the same combustion chamber, just liners in the exhaust ports. I would find a p90, I would not use the hydraulic, don't care what anyone says, the solid head will make more power, and you can run a performance cam in it. The P79 would probably be alright, although for more power, you need portwork anyway. Sell both heads and buy a p90, you can still find them. Quote Link to comment Share on other sites More sharing options...
David K Posted January 6, 2004 Share Posted January 6, 2004 I would find a p90' date=' I would not use the hydraulic, don't care what anyone says, the solid head will make more power, and you can run a performance cam in it.[/quote'] Now we are going to debate which head makes more power again? In no way are you going to notice which head yeilds more power. Unless you are spinning the engine up to 9,000 rpms, the hydraulic lifters will work just great. Look at all the modern 4 cylinder turbo engines making high horsepower for what they are, ie Mitsubishi turbos engines. They use hydraulic lifters, no problems there. End result, not much, or any of a difference, and never have to adjust a lifter again. Also, why would one go with a p79 head on a turbo engine over a p90(a) head. The round ports are TINY compared to the p90(a) head square ports. Just keep in mind, the p79 head IS designed for n/a applications. Quote Link to comment Share on other sites More sharing options...
Guest Boyd Posted January 6, 2004 Share Posted January 6, 2004 I am with Lockjaw. I talked with several Z gurus and have to say the majority said to use the P90 with mechanical lifters. A Z friend here in town said he ran very identical Z's, different P90's in each. The one with the mechanical lifters made more power and trapped quicker and faster. Quote Link to comment Share on other sites More sharing options...
Guest pintoz Posted January 6, 2004 Share Posted January 6, 2004 Thanks all for the replies. David, thanks for the link. You have convinced me to stay with the p90a. I do like the fact that it is much quieter than my p79. Quote Link to comment Share on other sites More sharing options...
awd92gsx Posted January 6, 2004 Share Posted January 6, 2004 If you can make a Mitsubishi Eclipse GSX run 10's with hydraulic lifters...why wouldn't you be able to do the same with a datsun? Quote Link to comment Share on other sites More sharing options...
David K Posted January 7, 2004 Share Posted January 7, 2004 I am with Lockjaw. I talked with several Z gurus and have to say the majority said to use the P90 with mechanical lifters. A Z friend here in town said he ran very identical Z's, different P90's in each. The one with the mechanical lifters made more power and trapped quicker and faster. Thats just purity at its best. So many things people say cant be done, and here on hybridz thry have been proven wrong, over and over, time after time. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted January 7, 2004 Share Posted January 7, 2004 If you can make a Mitsubishi Eclipse GSX run 10's with hydraulic lifters...why wouldn't you be able to do the same with a datsun? Have you seen how premetive the P90A lifters are? That's why. I ran P79, and I made power, and I'm sticking to it. Quote Link to comment Share on other sites More sharing options...
Guest Boyd Posted January 7, 2004 Share Posted January 7, 2004 So...what you are saying is that I shouldn't have bought your P90, huh? Quote Link to comment Share on other sites More sharing options...
yo2001 Posted January 7, 2004 Share Posted January 7, 2004 yap, j/k I just think it really doesn't make that much difference until you start making serious HP. like 300-400RHP. IMO That P90 should flow, I did some work on it. 8) Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 7, 2004 Share Posted January 7, 2004 I would still use the p90a vs. the p79. Always thought it was round port? guess not, oh well. I dont see anything wrong with a p90a for mild applications, its not like you couldnt do the p90 later. I prefer p90 for sure though, something about hot oil valve adjustments make you feel like a man Quote Link to comment Share on other sites More sharing options...
yo2001 Posted January 7, 2004 Share Posted January 7, 2004 P79 is round port. P90/P90A are square. P90A prolly do fine with stock cam considering the power peaks at 5500rpm or so. Shifting around 6000rpm. I've heard P90A doesn't like much over that. Quote Link to comment Share on other sites More sharing options...
David K Posted January 7, 2004 Share Posted January 7, 2004 I've heard P90A doesn't like much over that. Bigger oil passages to eliminate bleeding and stiffer/slightly longer springs in the adjusters to keep the lash pad on the cam lobe, and that problem goes away. Too simple, not rocket science. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted January 7, 2004 Share Posted January 7, 2004 well, bigger passegage will drop the pressure. PLus too much pressure/flow of oil on the head will starve the bottom end. I guess you can go with Turbo auto oil pump and shimmed about two washers and it might take care that though. Like I said, with modorate turbo set up, There isn't much point turning the motor more than 6k. Quote Link to comment Share on other sites More sharing options...
Guest szlash280z Posted January 7, 2004 Share Posted January 7, 2004 I have the P90A, I like it better than the old type except when I first start it. I am having some kind of oil problem that makes my lifters not pressurize fast enough so they tap very very loud for up to a minute or longer. There are a few things I am going to try to fix it though (better oil filter, fix my oil cooler lines). I was told to junk my P90A by the local Z shop and get a P90regular too, but I couldn't locate one. I would say go with what you have man. if you have a P90A already, stick with it. It's very quiet. the only think you can hear on my engine is the fan and the injectors. I like mine. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.