Scott_M67 Posted March 6, 2009 Share Posted March 6, 2009 Greetings everyone. I've tried posting this question on another Z car forum but got very little specific feedback (I'm sure its been covered multiple times but I can't find archived posts with specifics). My son just bought his first car, a '77 280X that we are rebuilding. We just gutted it down to the bare body last weekend which was fun and a great experience for him. My question is in regards to the engine performance mods. We currently have a N42 and a N47 head since that is what came with this project. (the N42 appears to have been rebuilt), the bottom end is still stock with the dished pistons which I understand yields a 8.3:1 compression ratio with these heads. I'd like to bump up the compression to around 9.8 and use the new cam that came along with the car. It is a reground External oiled cam on a Nissan core by Delta camshafts with .460" of lift and 260 degrees 212@ .050" so perhaps I should be looking to stay around the 9:1 compression target. I need to CC whichever head is best to use to verify actual compression ratio and figure out which head gasket to use. Its been suggested that an umilled N42 and flat tops with a Nissan head gasket puts this in the 9.8:1 ratio. I've read multiple ways to increase compression on the various Z forums but haven't found a real concrete answer. Do I install new ITM flat top pistons (with or without the two valve relief cuts) and just use one of the above heads OR do I need to find a P79 or P90 head to use flat tops. I did find datsungarage.com in which he mills a N42 head .080" and uses the dished pistons, is that a better way to go?? I'm sure this has been done multiple times before but I'm having a hard time finding all the info in any one spot. Which way provides the best bang for the buck? TIA Quote Link to comment Share on other sites More sharing options...
Challenger Posted March 6, 2009 Share Posted March 6, 2009 "280z" Get the book "How to modify your L series" and read the sticky on "l6 head specs, etc" in the L6 section. Id consider looking into the p90 flat top combo. Zhome.com has a writeup on it I beleive. Did you say you have both a n42 and n47 head or n42/n47 engine? Youll have to be sure you use the cam in the proper head. (externally oiled) As for not finding threads in the archives, keep trying... its there and its not hiding... Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted March 6, 2009 Share Posted March 6, 2009 Try to find the LEngine.exe calculator, if you Google it you can find a copy. It's nice to see all the options in one place. Flat tops with an N42 is around 9.8, Flat tops and a P90 will be 8.5, which is the same size as a F54 flat top and P79 head [the stock N/A motor when they switched to the F54 block] Pre-F54 N/A block pistons and turbo pistons have the same -10CC dish, P79s and P90s both have a 53.6 CC chamber Quote Link to comment Share on other sites More sharing options...
Scott_M67 Posted March 6, 2009 Author Share Posted March 6, 2009 Thanks guys, I found the Lengine calculator which is a quick easy reference. It appears that with flat top pistons, they may actually stick up past the deck by .03mm. If I just have the pistons flycut .50mm combined with a standard head gasket and a 44.6cc head I end up with a nice streetable compression of 9.30, and an acceptible quench which should work nicely with that little cam, this all assumes that the ITMs have enough material to trim. What do you guys think? Quote Link to comment Share on other sites More sharing options...
cockerstar Posted March 7, 2009 Share Posted March 7, 2009 Stock pistons pop up about that much iirc Quote Link to comment Share on other sites More sharing options...
Daeron Posted March 11, 2009 Share Posted March 11, 2009 Lengine.exe is nothing compared to this handy guy: http://www.ozdat.com/ozdatonline/enginedesign/ However!!! These calculators are estimation tools, and no internal part should be put together without being specifically measured. The calculators are tools to help you throw together junkyard engine pieces as thought projects. The next step is getting the hard parts, measuring, assembling, checking clearances, etc. Spend 50-75 bucks on a few books and read up on the subject. The investment of time will yield enormous dividends. Check the stickies in the L-series subforum for the specific titles; there are three or four (two or three engine specific, one or two more datsun/Z performance in general) books with similar enough titles that I run them all together in my mind. The publishers are even kind enough to make these four awesome tomes look very very similar, even though they are wholly independent works. Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted March 11, 2009 Share Posted March 11, 2009 Well if you are on a budget, new pistons = $ and pulling apart the block. Is the bottom end and/or was the engine in decent running condition when you purchased the car? Back in the day, I used the n42 head with a hotter cam, and I found it much more economical to mill the head, buy new lash pads, and simply bolt the head back on using a felpro turbo headgasket. Even with my stock dish pistons, the performance increase was noticeable. In my case, the stock bottom end was in excellent condition, and did not warrant pulling it apart. I drove it like that for many years before taking the plunge and building a monster N/A. Good luck with your project! Quote Link to comment Share on other sites More sharing options...
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