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N42 head help?!?


chb280z

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I took my N42 head to the machine shop to be pressure tested and bead blasted and I went in today to check on it and they said that it did not leak but there was a few small hairline cracks between the intake and exhaust valves. what do you think i should do? any help appreciated.

Thanks,

Chris

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Any good machine shop will be able to repair that. simply tear down the head grind out the crack i, if its not really deep, and weld it up. Could be pretty spendy though. What kind of setup are you planning to run. Could be cheaper to buy a built-up head from a known builder.

 

edit:I've seen this done on steel/cast iron heads but i don't see why not on an aluminum head

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I wanted to go the turbo route but the guys at the shop said "no way" the heat may drop the seat and you know what happens from there, but said it would be fine at stock CR for a while so i am kinda stuck here because i kinda want to finish the build and sell it so i can get a L28ET long block and start again. :confused:

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If your upgrading turbos there's a hole new list of things you'll need, depending on how much boost you want to run. As far as what head is best, you'll have to do some searching but as long as you have a turbo cam to go in that head you'll be fine. I dont think you will get the money that you put into that other head so I would hold off on that head for now.

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I wanted to go the turbo route but the guys at the shop said "no way" the heat may drop the seat and you know what happens from there, but said it would be fine at stock CR for a while so i am kinda stuck here because i kinda want to finish the build and sell it so i can get a L28ET long block and start again. :confused:

 

I guess I'm a little confused - I don't think there is anything different about the valve seats in the P-series heads, so by that logic, you shouldn't run any Datsun head with a turbo.

 

If they are filling and milling the cracks between the valves then you will most likely get new seats anyway, so just make sure they are installed with a really tight interference fit if you are worried about that.

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I was going to use the N42 because it was free and had the square ports. And had seen it done w/ decent results. But i think i will have them try to fix the head reassemble the long block and sell it.

 

TimZ: As for the seats they just said that they are worried of the crack getting worse and then dropping the seat.

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I was going to use the N42 because it was free and had the square ports. And had seen it done w/ decent results. But i think i will have them try to fix the head reassemble the long block and sell it.

 

TimZ: As for the seats they just said that they are worried of the crack getting worse and then dropping the seat.

 

okay - that makes sense. I wouldn't consider using it without fixing the cracks.

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You say "stock" block - meaning dished pistons. If so, then yes, that will "work". For a turbo application, you don't want a very high static compression ratio at all. The turbo itself will build up the dynamic compression ratio as boost builds. Ditch the N42 - someone out here on this forum will probably pick it up if the price is right. The P90 came out I believe in late '81, and is a far superior head (and the factory head) for the turbo application. Not a heck of a lot of difference b/t a N42 and F54 block from a layman's perspective, so that combo should work fine.

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OK so now i just need a P90 head. Anyone got one to sell? Oh and BTW didn't they (nissan) in late '81 put the P90 on all zx's N/A and Turbo and is there any difference? And how far should i let the machine shop go i mean it looks good now everything is nice and clean valves look good springs are good should i just have them put it back together and will I be able to recoup my money invested. meaning how much can I get for the cleaned and pressure tested head?

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Another idea kinda off topic but what about the N42 head and block w/ all stock internals but w/ L24 rods (9.85:1 CR)and a turbo running around 5-8psi. anyone done this w/ any success? Just an idea!?!

Also how are P79's for a Turbo because those are a dime a dozen?

 

 

It won`t work without custom pistons as the L24 rods are 3mm Longer than L28 units. Ending up with pistons coming 3mm out of the top of the bore.

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please read the stickies... I am all for trying to help people nail down answers to their specific versions of the same tiny issues that come up with every engine build, but only if the user makes it apparent that they have read the requisite posts that have already explained literally EVERY question you have asked.

 

If you can't take the time to research the engine you are building, then why should any of us take the time to answer the inane questions for the umpteenth time? We ALL know its alot easier to ask questions specific to our situation... but it is unfair to the forum members whose knowledge hoard could actually help you to expect them to teach you all the way from kindergarten. There are dozens of people on this forum posting daily who have achieved 400 horsepower with an L28ET, but none of them want to waste their time holding your hand.

 

I'm not trying to be a jerk, just letting you know that if you do some reading, you will learn more than what you are asking, and be much better off for it.

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For 1981 280ZXs Nissan began using 2 different heads. The P90 for the Turbo applications and the P79 for the non-turbos. For 83' model year Turbos, they started using the P90a with hydraulic lifters. Originally I thought all the P90a heads were all hydraulic, but I keep hearing that there are quite a few P90a heads that are not hydraulic.

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  • 2 weeks later...

Ok so i was wondering. W/ my N42 i asked this guy the Z Doctor in ronoke VA about using the head even w/ the small cracks between the valves and he said it should be ok to run w/ a turbo because w/ it beeing so old and having gone through so many heat cycles it shouldn't get any worse! How does everyone else feel about this? Also he said that the P79 flows the same as the P90 but I must leave the liners in to keep the air flowing good? So after talking to him this seems to contradict everything i thought to be true! HELP!?!!?!:confused:

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