Guest 280tuz Posted December 7, 2005 Share Posted December 7, 2005 Hi everyone, just joined this group because I have a 1975 280Z that n42 head has cracked. I used to have a 280ZXT which was totaled in a head on collison. I managed to get the p-90 head and turbo off it. The 1975 has dished pistons. From what I have seen in the internet a p-90 head would bring compression down to 7.4 without the turbo. I am unlikely to put the turbo on this old used motor because of possibly too much stress on the old block and the fact that I would have to re-do the whole exhaust system. I just want to get the old car running well on regular 87 octane gas. I wonder if the compression being at 7.4 would allow me to use cheap gas as well as keeping the same gas milage. I love the car and not interested in racing, just dont want it to be so gutless that I cant keep up with traffic. I also have a n-47 head but unsure of it's condition yet. Also, if the 1975 has dished pistons, does that mean I'ts ok to run a turbo, or what other mods would have to be done to the block. Maybe next summer I will upgrade it with a turbo. Any help I would appreciate. Thanks. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 7, 2005 Share Posted December 7, 2005 You should be able to run 87 on the P90 with flat tops at 8.3:1 or whatever it ends up being. You will lose some bottom end for the lack of compression, and you'd probably lose some mileage too. Quote Link to comment Share on other sites More sharing options...
Guest 280tuz Posted December 8, 2005 Share Posted December 8, 2005 So 7.4 is about what it would be with the existing dished pistons using a p-90 head w/out turbo, sounds like that may not work too good. What do you think about the N-47 head? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 8, 2005 Share Posted December 8, 2005 N47 would be essentially the same as the N42 you have now, but with the exhaust liners that reduce emissions. That is definitely the way to go IMO if you aren't going to change pistons or do something else to get that compression up for the P90. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted December 8, 2005 Share Posted December 8, 2005 Hey J ... I don't know how much you want to get into your engine but I think your best bet for a fun N/A car would be to rebuild your short block with flat top pistons and throw the P90 head on there and from what I've read the P90 head was the best flowing of all the heads. That would give you a CR of 8.52:1 (acording to the L engine calculator). with that compression you would be able to run 87 octain with no problem and still have a "zippy" little car. While you're at it through on a 60mm throttle body(from a 240sx) on instead of the 50mm TB that is on the car now and that should make your car a lot of fun to drive untill you turbo it. If you don't want to rip into the short block then just through the N47 head on there. it'll work great im sure. rock on Z people Quote Link to comment Share on other sites More sharing options...
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