Gavin Posted December 16, 2005 Share Posted December 16, 2005 Just curious about using the early L28 block (N42) with a N47 head, if it would raise or lower my compression. I have both at my disposal.. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted December 16, 2005 Share Posted December 16, 2005 Hey gavin, we need more info. in order to answer your question. for example... are you going to use flat top pistons or dished pistons are you going to bore the block, if so how much also the N-47 head came standard with the N-42 block with dished pistons and a compression ratio of 8.29:1 from 75-80. if you're woundering if an F54 block would give you different compession with an N 47 head the answer is no. All of the L-28 blocks have the same bore and stroke. different heads, pistons, and head gaskets will affect the CR the block doesn't matter (unless it's an L24 (e31, P30) or L26 (P30)). I hope this answered some of your questions Rock on Z people Quote Link to comment Share on other sites More sharing options...
Gavin Posted December 16, 2005 Author Share Posted December 16, 2005 Yes it does. I thaught I had read that the earlier motor had different pistons to match the different head but guess not. By block I really meant pistons (I have both whole motors, and was hoping maybe I could just swap the bottom over). So, to rephrase my question, will the N47 head combined with the earlier pistons (otherwise stock) yield a higher CR than a stock 78 motor. But you tell me they are the same pistons, if I understood. Thanks! Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted December 16, 2005 Share Posted December 16, 2005 hey Gavin, The 75-80 L28's all came with "dished" pistons. You can put "flat top" pistons from an 81-83 non turbo into the block and raise the CR with the N-47 head to 9.82:1 In my personal oppinion a great CR for a Naturally aspirated L28. If your every thinking about going "turbo" that might be a the edge of a do'able CR. When you say you have "both blocks" what do you mean? the only two L28 blocks were the F-54 and the N-42 the N42 cam with dished pistons the F54 had a choice of dished or flat top depending on if it was turbo or NA. do you mean that you have an L26 or L24 block? Also what are the 2 different heads you have? N-47 N-42? N-47 P-79? Different heads can give huge differences in CR. I hope that cleared things up for you Rock on Z people Quote Link to comment Share on other sites More sharing options...
Gavin Posted December 16, 2005 Author Share Posted December 16, 2005 I have both complete motors, the N42 and the later one with the N47 head. So I have an N42 and an N47 head and two identical bottom ends. From what I have read I'm just going to sell the N42 head and build the block to mate with my N47 head later. What you said about using the N/A ZX pistons is exactly the kind of setup I had in mind when I started this thread and I think I will go for that. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted December 16, 2005 Share Posted December 16, 2005 Good times .... the N42 head and the N47 are almost the same (they have the same CC's), the only difference is in the exause ports. the N47 has rounded exaust ports with steel liners that heat up to burn up unburnt fuel in the exaust gasses. its suposedly a great flowing head. On the other hand the N42 head is legendary for it's performance. If you decided to sell the N42 you should get close to $200 bucks for it. Which ever head you go with make sure you rebuild the thing. those brass valve seats suck and a new 3 angle valve job wouldn't hurt. I'm running an N-42 head with flat top pistons and SU carbs with headers and electrick dizzy and my Z is awesome fun to drive. Good luck, and keep us posted on your build. Rock on Z people Quote Link to comment Share on other sites More sharing options...
Gavin Posted December 16, 2005 Author Share Posted December 16, 2005 Yeah I read that about the square port head. I alse read that for a mild race/street engine I should go with the N47 or even better the Maxima version. The money sounds good to me. Otherwise I'm thinking I'm going to clean up the head, do a valve job like you say, and unshroud the valves. Later on, after raising the CR, I'll go for the 260deg cam and after that I'd be happy with whats under my hood. Thats just what I'm thinking of doing as of right now, subject to change at any time - based on feedback from you guys of course! Thanks for the help. Oh and BTW right now I'm running the N47 motor stock with MegaSquirt, soon to upgrade to the ZX dizzy for spark tuning. I'll definitely post up my tuning once I get the wideband in, since I know we are lacking N/A basemaps I think a tuned stock setup would be a good contribution. Anybody want to trade a MN47 for a N42?? Quote Link to comment Share on other sites More sharing options...
z-ya Posted December 16, 2005 Share Posted December 16, 2005 I think you should make a decision based on what exhaust manifold/header you are using. If it isround port, stick with the N47 or MN47. The MN47 has a similar combustion chamber as the "P" heads, so if you can get one of those, that's what I would use. If you have a header with square ports, use the N42, which has the same combustion chamber as the N47. I built a street engine for my Wife's 280Z with flat tops and the MN47 head. It's got nice low end torque, and decent power up to 5000 RPM (stock exhaust manifold). Quote Link to comment Share on other sites More sharing options...
Gavin Posted December 16, 2005 Author Share Posted December 16, 2005 I have the stock N47 ex manifold right now so I'm still flexable in that area. So what compression would the MN47 combined with the flat tops give me? Also, how much does each .1mm of gasket thickness change the compression over stock, approximately (and what is the stock thickness?)? Looking at using the Nismo .6mm compressed gasket for some more squish.. If there is a guide to all of this that I missed in my search please feel free to point me towards it. Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted December 17, 2005 Share Posted December 17, 2005 Hey gavin, That MN47 head with flat tops will give you something in the ball park of 11.3:1. Thats pretty risky, but you are running megasquirt so you can really controll your air fule raito. the 1mm head gasket raises the CR about .3 or so if I remember correctly compaired to stock head gasket. now that I think about it that 11.3:1 CR might be with dished pistons so flat tops might be more like 13:1, a bomb waiting to happen. Rock on Z people Quote Link to comment Share on other sites More sharing options...
Gavin Posted December 18, 2005 Author Share Posted December 18, 2005 Oh my I didnt realize the compression gain I would get from the MN47. How much do these heads go for? Quote Link to comment Share on other sites More sharing options...
Gavin Posted December 18, 2005 Author Share Posted December 18, 2005 Oh sweet http://www.atlanticz.ca/zclub/techtips/calcs/engine%20builder/index.html Quote Link to comment Share on other sites More sharing options...
zeiss150 Posted December 18, 2005 Share Posted December 18, 2005 gavin, check this one out ... I like it better http://flzclub.com/downloads.htm Quote Link to comment Share on other sites More sharing options...
Yokohama Posted December 19, 2005 Share Posted December 19, 2005 The Maxima N47 can be a great head, if you grind the base of the exhaust liners into the base of the valve seat. The exhaust liners in the head can actually help the exhaust gas make the turn inside the port and out into the exhaust manifold.If you are interested, I have a spare N47 head, PM for details. Quote Link to comment Share on other sites More sharing options...
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