J Taylor Posted July 11, 2002 Share Posted July 11, 2002 I took my 77 to the drag strip last night and the 1st passes were back to back 9.76 and 9.77(approx 15.2 in the 1/4). I was really impressed with the times considering the car is stock except for a header and full exhaust. I got home and was reading about the different heads and stuff and it turns out my car has the stock n42 block with a p79 head which gives it a 7.8:1 compression ratio??!!??!! I have a e31 head sitting here and access to a e88 for cheap. Which would be the better head? Would the compression be too high with the e31? Is there another head that would be better suited to the motor? I want to be able to run on pump gas without a problem. Bare with me....I'm used to the turbo stuff and still new to the na route. Thanks alot, JT Quote Link to comment Share on other sites More sharing options...
J Taylor Posted July 11, 2002 Author Share Posted July 11, 2002 ALso, will the fuel injection be able to compensate ok for the higher compression? Thanks, JT Quote Link to comment Share on other sites More sharing options...
Guest LIghtningZ Posted July 11, 2002 Share Posted July 11, 2002 Hey, jay i just went thru a big thing with my heads (75--280Z) your kind of unclear about what kind of block and head you have can you specify i think we can help i know that DAW will definetly try to help you and so will i try to look thru my posts on this forum and also bangs posts !! p.s. the F.I. should hold up just fine!!! Quote Link to comment Share on other sites More sharing options...
J Taylor Posted July 11, 2002 Author Share Posted July 11, 2002 Ok. What I have is the n42 block (dished pistons) and the p79 head. From what I have found online this makes ~7.8:1 CR. After reading a bit more I think what I am going to do is find a zx short block with flat top pistons and get my friend's e88 head. I found a square port header from another friend for cheap (anyone need a round port 6-2-1 header?). I think I can pull this whole motor off for $100-200. Only thing is, will I be able to run this setup on pump gas? I am open to suggestions so if there is another setup that would work better shoot it at me. Thanks, JT Quote Link to comment Share on other sites More sharing options...
Mike C Posted July 11, 2002 Share Posted July 11, 2002 The FI should be able to compensate, especially with tuning. The E88 head will have to be modifed to be compatible, needs to be clearanced for injectors and some extra holes added. Just compare it to your FI head when you get it off. Quote Link to comment Share on other sites More sharing options...
J Taylor Posted July 11, 2002 Author Share Posted July 11, 2002 Alrighty. I forgot I also have a n47 head on a parts car behind my shop so that one is a possibility as well. Maybe this head with the flat top short block? JT Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted July 11, 2002 Share Posted July 11, 2002 Don't use the E88. Mill the p79 head and shim up the cam towers and use a thicker lash pad to compensate. A P90 head milled would be good too. I am going to be putting a milled just a little P79 on my flat top engine in my 260, hopefully pretty soon. I have the head done, I just need to replace the valce stem seals and get a cam ground. We had a guy down at Ira's that milled a P79 and out it on a flat top bottom end with a cam and header and SU's that rocked. He ended up running my side draft webbers and I think he ran some 8.40's in the 1/8th mile. Now that was a getting down car. Quote Link to comment Share on other sites More sharing options...
J Taylor Posted July 11, 2002 Author Share Posted July 11, 2002 Funny you should mention that. I just got off the phone with Ira a few mins before I got online and he told me the same thing about the same car. Can you give me some specifics on how much to mill, etc? I am looking for around 10:1 CR. I was really hoping to stay away from machine work and keep this as low budget as possible since I just dropped a small fortune for parts for my other z but I guess I can take some more time and spend some more money if need be. I would appreciate some specifics if possible. Thanks alot, JT Quote Link to comment Share on other sites More sharing options...
Guest V8wannabe Posted July 12, 2002 Share Posted July 12, 2002 Download the nifty little Lengine.exe program. It will allow you to play with various parts combinations. Lengine good luck!! Quote Link to comment Share on other sites More sharing options...
Guest V8wannabe Posted July 12, 2002 Share Posted July 12, 2002 You'll find it under the Technical Articles link Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted July 12, 2002 Share Posted July 12, 2002 My .02 cents.... E31 + flat top pistons = too high CR for pump gas and stock FI. Not sure about the actual comp ratio but I do know that an E31 will give higher compression than an N42, and when I put an N42, NOT SHAVED at all, on an L28 with flattops I had mad pinging problems with the stock FI. I know this is due in part to the N42's chamber design, but the 10.4:1 CR didn't help. It also depends on what cam you go with. I stuck with the stock cam which also added to my problem. Personally, after doing a ton of research online I believe the P79 and P90's are the best flowing and best heads for performance buildups, but you need to shave and shim to get the kind of CR you're looking for. By the way... not sure what kind of tuning you can do with a stock FI exactly... in the end I had to go with an aftermarket adjustable fuel pressure regulator to boost my fuel pressure, before my car would run without detonation. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 12, 2002 Share Posted July 12, 2002 I'm pretty sure the flattop piston/N42 combo has been done sucessfully more than a few times. Seems to me that was the hot ticket a couple years ago for NA performance using cheap stock parts. CR should be around 9.8:1 with this setup, though the N42 chamber design isn't ideal as previously mentioned. Norm on Zcar would be the one to ask I suppose, he's played with most of those block and head combinations. I'm toying with putting a flattop piston block under my N42 head, so please post with any info gained! Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted July 12, 2002 Share Posted July 12, 2002 If memory serves, that head was milled about 110 thousandths, which was to much for street use. I would stay in the 80 thousandths range. I believe that is what I ran on mine and had no problems with 89 octane. He also ran a BIG crower cam. It did not hit its powerband until about 3500 rpms, but when it hit it, it thumped. I have the cam at home right now, and am going to be seinding it in to crower to see if they can fix it. I know they can replace it. I may have them cut it down a little. You need to run a milder cam with the fuel injection. There is a Schneider 274 duration 480 lift cam that is pretty sweet, and I think fuel injection will tolerate it fine. MSA can hook you up on that, and if you shim the cam towers up and tell them how much, they should be able to set up on a lash pad too. Tom ended up putting a 3 inch exhaust on that car with a 3 in blowmaster muffler. Man it was loud, and it hit like no bodies business. You should have seen it when he took it down to the drags in Tuskeegee. Pop the hood, and it is like rats on cheese. They could not beleive that car had a six in it. We always got accused of having V-8's when we ran cams anyway. You tell people you have a 6 and they were like Yeah right. I always said, I will be happy to open the hood. Let me know if you get hung up anywhere. At the rate I am going, it will be September before I get this rag running. Good luck. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted July 12, 2002 Share Posted July 12, 2002 Again, the N42 IS a good head, and not too long ago everyone thought it was a great head to use for performance buildups. Don't get me wrong you can definately make this head and flattop piston combination work. Norms shaving method of shaving down the head to alter combustion chamber size/shape is just one way of cutting down or eliminating detonation problems. Again, simply switching to a mild street cam with between .450 and .480 lift and around 270-280 duration would also go a long way towards keeping this combination from detonating. Again, you will also really want some way to really get in and adjust your fuel mixture and curve if you want to maximize the power potential from so much better airflow. 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.