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PostPosted: Mon Dec 12, 2016 7:08 am 
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Can I swap out just the cylinder head on my 1983 280zx with an N42 cylinder head without any modifications?


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PostPosted: Mon Dec 12, 2016 5:12 pm 
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Location: Long Island, N.Y.
Calling Frank T... calling Frank T. He's Z man that might be able to answer your swap question.

Howard J

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1985 300ZX- GLL Dark Pewter Metallic - Survivor


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PostPosted: Mon Dec 12, 2016 7:10 pm 
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Location: CT
Hi ennslee ~ YES, it's a very popular swap and almost everything just lines right up. Remember to replace the soft valve seats with hardened seats because you will be running unleaded fuel at hotter temperatures. The N42 had big valves (deeper breathing) and smaller combustion chambers because it was made for the dished-top pistons of the turbo engines. Stock, the N42 gave the turbo engines about 8.8:1 compression ratio.


But regardless of which head they had after that, all engines after 1981 had flattop pistons with larger combustion chambers. So by combining the small combustion chamber N42 with the flattop block of the 1983, you arrive at about 10.3:1 CR.

You don't specify which head you're removing from your ZX, so be aware there might be a difference btwn the N42 exhaust ports and your present manifold. You'd solve that with a set of exhaust headers.

If this is just a matter of conveniently replacing a bad P90 head with an at-hand N42, you will notice some performance increase. If you're doing this to seek a hotter engine, take this opportunity to install a bumpier cam, a set of headers and have the "new" cylinder head shaved straight. Just remember however much you shave off the bottom face of the "new" head, you must add the same measurement in shims beneath the cam towers to raise the camshaft back to the original height to keep the timing chain properly taut.

Also don't forget your car will be on a 94-octane diet from now on.

I highly recommend you read our member Bryan Little's "DATSUN Z GARAGE" website. You can find a direct link to it on our Home Page, in the left margin. I doubt there is anything Bryan hasn't done with a Z engine.

Please keep us posted with your progress and let us know how you like the result?

Z ya,
Frank T

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1970 240Z


Last edited by Frank T on Tue Dec 13, 2016 3:40 pm, edited 1 time in total.

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PostPosted: Tue Dec 13, 2016 3:03 am 
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Yes, the old head is a P90. The car runs fine, but I wanted to upgrade it in someway. Thanks for the info. I'll keep you posted.


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PostPosted: Tue Dec 13, 2016 12:48 pm 
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Good ~ the P90 and the N42 have the same shaped exhaust ports, so you could keep your stock exhaust manifold. You'd just need to replace the gaskets.

Not meaning to rain on your parade, but this swap will put about 2 more compression points of pressure on top of your pistons. If your rings are worn (80,000 miles or more) you might see some significant blow-by* and smoke out the exhaust. Your increased combustion pressures will also put a lot more force on your lower-end bearings, and if they're worn too, you might experience a loss of oil pressure, bearing rattles and bells, and eventually an engine mechanical failure of some kind.
Basically, this swap would make an old man try to run like a young athlete...for awhile. Your idea is a good one and will certainly increase your performance. But a ring and bearing job (even a cheap one) would be highly recommended along with the swap.

*Blow-by pushes air/fuel down past the rings and can really pressurize your crank case with air/fuel vapor. While most cars today have a positive crankcase ventilation system (PCV) to relieve some of that pressure, there have been instances where the fuel/vapor has been forced up the distributor shaft until it reached the distributor plate, where a simple spark from the points ignited it. That results in a blown-off distributor cap at best and a blown up crankcase at worst.

The N42 has an external oil spray bar. The 280ZX might have a hollow internal oiler camshaft (I don't recall). That won't matter as long as you swap the whole head and cam together. The oil galleries are the same and will work on whichever oil system you use.
Frank

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1970 240Z


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PostPosted: Fri Dec 30, 2016 9:16 am 
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Location: rhode island
The N42 was 75-76 280z's, and the blocks had dished pistons, then in 77-78 they put in flat top pistons and used the N47 head with larger combustion area. (79-80, nothing good) Then in 81 they came out with the turbo block, F54 stamped on the side. Only made until 83, and dish pistons for the turbo, and flat tops for the N/A. 81-82 turbos had the high flowing P90 head, and if shaved down (.80) and installed correctly is an awesome engine combo, but why ruin the head......(83 just had hydraulic lifters, P90a,) (N/A's had the P79 head) So going with the N42 is a great way to go. Cheap instant horsepower! You have a good combo, your F54 and the N42, those heads are very rare to find these days. Have the steel valve seats put in then have it milled to the minimal just to clean it up, and have it pressure checked first, and use high grade valve seals. Another good combo is the F54 and the E31 with 280 valves installed. BTW, the combination of Datsun engine parts makes for a very long list.


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PostPosted: Thu Feb 16, 2017 1:36 am 
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Location: CT
So, how did this work out, Ennslee?

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PostPosted: Fri Feb 17, 2017 12:25 pm 
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I was wondering that myself.


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PostPosted: Tue Aug 15, 2017 3:12 am 
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I finished this engine mod finally and on initial start up, the engine immediately went to 4000 rpm's. I have checked or replaced everything I can think of, such as, the mass air flow meter, idle control valve, and the throttle valve switch and no change. I did have the cylinder head rebuilt before I installed it. I also added headers, new fuel injectors, new spark plugs, new air filter, new O2 sensor and new exhaust. The car ran fine before the mod was done. Does anyone have any ideas of what the problem might be?


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PostPosted: Tue Aug 15, 2017 8:35 am 
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Location: CT
Well, at least your new engine is eager to go! :lol: (Sorry)

Always check the simple stuff first. Starting at your gas pedal, trace each bit of the throttle linkage to make sure it has full range of motion and is returning to "zero" when you lift off it. You did a lot of surgery to the upper end of the engine; you might have changed something you didn't intend to. I think I might disconnect the injection system from the throttle linkage (and work it by hand at the engine) just to eliminate some mechanical maladjustment of the linkage first?

After that, engine speed is only governed by air/fuel intake and timing. One of those is not how it should be and needs adjustment. Consider possible vacuum leaks anywhere in the intake system. A leaky gasket can feed air into the engine the same way an open throttle would.

What problems did you encounter during the swap?

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PostPosted: Mon Aug 21, 2017 11:48 pm 
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I did not find any problems with the throttle linkage. In fact it wasn't even attached to the peddle yet on initial start up. I did not encounter any problems during the swap. Everything went as planned. That's why it through me for a loop when I started it up for the first time. When you say there might be an air leak between the gaskets, that might be it because now that I think about it, I think I may have the wrong headers on it. I think I put round port headers on the square port cylinder head. That's bad news, if that's the case, because I will have to pull the engine again.


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PostPosted: Tue Aug 22, 2017 10:29 am 
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I referred to leaking gaskets anywhere on the intake system, which might let ungoverned air get sucked into the engine and make it race like that. The wrong combination exhaust/intake gasket *might* allow that to happen, but I'm struggling to picture how it might.

We already determined that the two heads you worked with (a P90 and the N42) had the same "square" exhaust ports, so unless you actually installed the wrong gasket (round gasket on a square port head), I shouldn't think that would be your problem. If your exhaust manifold or headers worked with the P90, they will fit the n42 as well.

If you failed to TIGHTEN the manifolds according to directions, that might have allowed an air leak (or leaks) around the intake port(s) which would suck in more air than you wanted; the only air entering the engine should come thru the induction system (fuel injection system).

It's also necessary of course to use a new gasket under the manifold, not try to re-use the old compressed one. The L- series engines use a combination Intake/Exhaust gasket which must be replaced after use. Re-using the old one will almost certainly cause leaks in both directions.

Manually try to close the throttle body while it's still disconnected from the pedal. Make sure it has full range of motion. Attach any return springs and make sure there's nothing mechanical (a loose bolt?) stopping the linkage from closing fully.

With the engine running (racing fast), close off the air intake completely (place your hand over it? is that safe?) and try to choke the engine. If it continues to run, it's getting air from someplace else and you must find that leak.

Physically check every rubber hose connected to the head. A single leaking (or disconnected) hose can allow enough of an air leak to cause exactly what you're describing.

If you have any carb starter fluid you can spray it around the COLD running engine gasket and hose areas. If it races even faster when you spray an area, that's where your leak is. Don't stop testing when you find one leak; there may be others. Have a buddy in the seat ready to kill the ignition upon your command.

Even if everything is wrong, you shouldn't have to pull the engine. Disconnect the exhaust headers and work with the head directly.

*(NOTE): When we discuss this work, I use a lot of very basic mechanical terms and procedures. You almost certainly already know about them, so I don't mean to insult your experience by mentioning them. Many other people (many visitors) read this website and some might be novices to mechanics and not understand what we're discussing. Since there is no way to know what level of experience our audience has, I think it's safer to use common terms and entry-level explanations. I fully recogniZe you are already wayyy ahead of the beginner's curve, and I mean no insult by using basic terms or explanations. Please forgive me if I tell you something you already know ~ I'm not only writing to you.

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PostPosted: Wed Aug 23, 2017 9:53 pm 
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Thanks so much for your help. I will check everything you mentioned.


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PostPosted: Sun Sep 03, 2017 10:49 am 
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Joined: Wed Jul 23, 2008 2:38 pm
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Location: rhode island
Not your header, the worse that can do is leak exhaust. Your Air Flow meter probably needs to be recalibrated inside the black cover, as long as all else is well as far as no intake leaks. Other thing is the Idle control to look at. Unplug the TPS and see if that makes a change, they have an adjustment as well. Just off the top of my head if this helps, but check and recheck everything.


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