Jason81NA,82RBtt Posted January 10, 2003 Share Posted January 10, 2003 I'm think of replacing the F54/N47 comb with a P90 head. I want to get the head shaved. I noticed that some of the website say to shave it .080 and others say .100. Which is correct? I also assuming this is metic measurement, right? I can't seem to find out what headgasket to use. And Even if I use the Felpro(1mm) gasket I'm only getting 9.84:1 comp ratio. So I figured I'd test it using the 0.6mm headgasket. I then get a 10.27:1, that's more like it! But I figure that is is somewhat equal to taking off .120mm+ off the head as far as the timing chain is concerned. Am I doing something wrong or are the websites stating a higher figure for the comp ratio.I'm wanting a 10.2:1 to a 10.6:1 or I might as well keep the F54/N47 combo. Thanks for any help JasonRB260ZX P.S. I thinking the p90's peanut shaped chamber will allow me to run more nitrous safely. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted January 10, 2003 Share Posted January 10, 2003 .080 and .100 are in inches. Search the archives and you'll find a few semi-intelligent discussions of the P-heads vs. the N-heads. I wouldn't go to the trouble of shaving and shimming a P90. Then again it might be a good experiment, IF you go to the trouble of ensuring you don't change cam timing or compression ratio. While you're at it, you may as well do an N42 swap as well to help us quantify the performance diff between round/linered exh. ports and the supposedly better-flowing square ones. Quote Link to comment Share on other sites More sharing options...
Guest Zcarsmakemyheadhurt Posted January 10, 2003 Share Posted January 10, 2003 Turbo car J??? Quote Link to comment Share on other sites More sharing options...
yo2001 Posted January 10, 2003 Share Posted January 10, 2003 I doubt it's going to be a turbo car. 10:1 compression. .080" with flattop would be around 10:1-10.5:1, .100, you'll be closer to 11:1. I've seen a P90 set up with .120" shaved off with big crower cam. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted January 15, 2003 Share Posted January 15, 2003 im with Dan get a N42 but then again i am still sitting on a stock pile from the early 90s Quote Link to comment Share on other sites More sharing options...
Synlubes Posted January 15, 2003 Share Posted January 15, 2003 Head info Go to the P-90 page. More head info Quote Link to comment Share on other sites More sharing options...
Guest 2adz Posted January 15, 2003 Share Posted January 15, 2003 I have the shaved P90 setup on my 280. I had it shaved .080 and then replaced the valves with ones from a 1976 280Z head which are .080 longer than the P90 valves and then shimmed the cam towers up .080. The head is sitting on top of an F54 block. I am very happy with the head and the setup, the car is very strong. Quote Link to comment Share on other sites More sharing options...
Bob_H Posted January 16, 2003 Share Posted January 16, 2003 Jason, I had an interesting discussion with John of Zspeedauto,(posts here as such), about some of the Maxima heads. I can't verify the info, but it is worth checking out. First, we are all familiar with the N-47 "Maxima" head on the 2.4L motor. Apparently there was a N-47 on the 2.8L Maxima that has square exhaust ports,(no liners), and the supposedly more desireable combustion chamber. He wasn't 100% sure that it is on every 2.8, but he saw it on more than one Maxima. It is intriguing to say the least and most certainly worth the look. I myself am very interested in what exactly is the deal with a 2.8L Maxima head....as I wasn't even aware Maxima's had a 2.8L, but I don't know squat about Maxima's anyways. Don't know the combustion chamber size or any other info, but I think it is worth the look. If you are running NA, and only a 2.8L, your money is much better spent modifying the N-42 or 47 to work vice all the setup and timing issues with a shaved P-90. Remember, you must then re-check the overall cam timing to ensure it is occuring when you want it to. The timing chain slack will be an issue at .080 or .100 inches. It may only be a few degrees, but that might negate any positive effect of the chamber over an equal compression ratio N-42..... Food for thought. I'd love to find out more about the 2.8L maximas if anyone has info. -Bob Quote Link to comment Share on other sites More sharing options...
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