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saridout

some questions about cylinder heads and my block

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as some of yall know, i overheated my 76 280 recently, and my machine shop tells me that the head is shot. now i'm shopping around for a new one, and i'm a little confused. my head is an N42. i've been led to believe that an N47 will fit my year and model too. what is the significance of these codes? what heads will fit my car?

i'm also a little concerned about my block. the cylinders have some striation in them, and though my nail doesn't catch on them when i run my finger around a cylinder, it doesn't feel too smooth. i can't really afford to get them bored, but i don't want to get everything back together again to find out that the block needs service. should i be concerned about these striations, or are they typical?

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Are they straight up and down or are they kind of like a cross hatch pattern (I.E - like a big X all around the cylinder) If they are like a big X pattern that's pretty normal...helps the rings seat to some degree during break-in and also bore lubrication.

webdawg1

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That probably indicates some contamination, be it from carbon or other things have been captured by the rings and has been dragged against the cylinder wall. It sounds like you will need at least a hone, if not a rebore.

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Most likely a honing will do the job , unless they are deeply scored. Knobi is correct and if you can get by honing you can use the same pistons.

Basically the blocks are all the same . the 280s all have dished pistons but the different years the heads changed , but will still fit. The differences are the compression that is archived.

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Note that the N47 head has round exhaust ports with internal liners designed to heat up and burn any fuel that doesn't get burned in the combusion chamber. Some think these flow less than the square port heads, but there doesn't seem to be any conclusive evidence on this. Using a round port head with square exhaust manifold is thought to be fine, but not the other way around. Also note that there was a different version of the N47 used on Maximas with a L24 block that had a smaller combusion chamber and valves than the Z version of the N47 for the L28. I've heard of people using this head but believe that they require significant modifications to run pump gas due to the higher resulting compression ratio.

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i've found a guy locally who says he has a head off of a running '83 ZX, and i'm guessing it's a P90. if i went with a P90, what kind of mods am i going to be looking at? would my compression lessen dramatically? would i need to buy flat-top pistons?

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Could be a P79 or P90......With flat tops, either head would give you about 8.5 to 1. To increase compression,you'll need to get someone to shave and shim the head. .080 cut will give you 10 to 1, but the cam towers and valve springs must be shimmed .080 also.

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Note that if you put the P90 or P79 head on your dished piston motor the compression ratio will only be around 7.2:1

Edited by blue 72

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argh, why do people only take photos of the spark plug side of a head?... i'm trying to see if an E31 has rectangular exhaust ports. would i need to mod anything if i used an E31?

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E31, E88, N47, P90 = Square port

N47, P79 = Round port

Those are just the most common heads from the U.S.

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E31, E88, N47, P90 = Square port

N47, P79 = Round port

Those are just the most common heads from the U.S.

You mean:

E31, E88, N42, P90, P90a = Square port

N47, P79 = Round port

Also, if the head is original to the '83 and it is in deed a P90 variety it's going to be a P90a. What's the difference you ask? I'm glad you asked...the P90a has hydrolic lifters. From everything I have ever read you do not want the hydrolic lifters. Do a search on this topic and you should find plenty of reading material to keep you busy for a while. ;)

Also for what it's worth there were two different versions of the E88 head made, I believe that the better version was original to the '71 and '72 cars while the less desireable one came on the '73 cars. Again, do a search on this topic and you'll find more detailed info.

One good resource is Bryan Little's Z Garage site: http://datsunzgarage.com/

Edited by texasz

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after angsting over this for weeks, i've finally decided to just buy a well-rebuilt N42. no fuss, no muss, and i'll never have to worry about it again. thanks for all yall's input. i really appreciate it.

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