whats better p90 or n42 head

[DAW]

P90s are going to be far scarcer than an N42 because most are in use as the OEM/head of choice for the L28ET, whereas the N42 is from a stock 280Z L28E and in much higher production volume.

 

One twist is that there are P90 heads on some Japanese market (JDM) L28 non-turbos that come in through the used engine importers. Some of these have been bought, N42/47 head grafted on for a 10+:1 engine, and freeing up the P90 head to build a turbo engine. DAW

[Lockjaw]

P90 is the best. No matter what anyone else says, a P90 is the best. Repeat that 100 times.

[TimZ]

Originally posted by Lockjaw:

P90 is the best. No matter what anyone else says, a P90 is the best. Repeat that 100 times.

Oh Jeez. Here we go ...

 

Do a search on this subject - I don't want to go into this again, unless some new info comes up...

[Lockjaw]

No sense searching, Bob H will weigh in after while and back me up.

[Bob_H]

You know better Craig! I will NOT back you up on this one !

Sean, I refer you, as everyone, to the search function. It works rather well, and can save you a lot of questions. But since you are new, I took the liberty of doing it for you,(lets see how often I am this nice). Here is a thread with 2+ pages about the two heads.

You should find it entertaining. We did!

Weber head thread

And Lockjaw and I are not mortal enemies. We just have a disagreement on the best head for the money.

Enjoy,

Bob

[Guest Anonymous]

just wondering the difference, are p 90 heads hard to find?

[Lockjaw]

Yes we do disagree but aren't you running a P90a?

 

 

Actually that thread had a lot of good info in it.

 

What we really need to do is take all the heads, put them on the same motor, and dyno them all. Of course, I think we should make the combustion chambers all the same CC, that way we could eliminate compression differences. If we did that, I am confident that the P series heads would thoroughly trounce the other ones.

 

But that is just one guy's opinion.

 

Originally posted by Bob H:

Bolting an N-42 to a flat top motor produces a CR near 10:1. That is the big reason why it will produce more power than a 8.6:1 motor, head nonwithstanding. Now, bump that P-79 up to the same CR, and it will produce more power. I was getting carried away when I responded. Guilty.

-Bob

Sorry Bob, had to do it. For those who don't know, the P79 is essentially a P90 with exhaust liners cast in the exhaust runners.

 

See sometimes we agree.

[Dan Baldwin]

Lockjaw, I luv ya man, but you couldn't be any more full of it. I *thought* we had agreed to disagree on this, but DAMN you're thick-headed.

 

You need to show us AT LEAST ONE of the following:

1) a 235rwhp N/A L6 running on pump gas

2) a 320 hp N/A L6 race motor

3) a sub-13 second N/A L6 car running on pump gas

with one of your "magical combustion chamber" P90 or P79 heads. The N42 is such a piece of crap that I know of three that have accomplished the above.

 

The N42 is THE bolt-on head to have for performance. After you shave the bejeezus out of a P79 or P90, they're almost certainly in the SAME ballpark (not in another league, I'd bet money).

 

OPINION doesn't count for SQUAT until it is backed up with some hard data.

 

Sean, the first thing you need to do for an N/A L28 application is have flat-top pistons ('80?-'83 280ZX non-turbo). In MY opinion, the best/easiest setup is the 280ZX flat-top piston bottom end with an N42 (or N47, or big-valved '71-'72 E88) cylinder head. Presto, 9.8:1 compression L28, no sweat. Lockjaw's precious P-series heads will get you 8.5:1. If you want to butcher .080" off of a P-series head, or trust your local machinist to do it, and then monkey around with cam tower shims and lash pads and STILL not be able to get the stock valvetrain geometry, and have to worry about excessive cam chain slack, you can do that, too. You might even get an extra 2-5 hp, but then again you might get LESS hp. NOBODY on this forum or elsewhere that I've looked has demonstrated the superiority of the P-series combustion chamber. I do hear a lot of talk about how much better it looks and about "quench area". That doesn't count for much at the engine dyno, chassis dyno, drag strip, and road course, though.

[yo2001]

Dan, there is a hard number from the factory. The late zx motor with P series head produced 10 crank HP more than earlier zx with N series head. And don't say it's because of the compression difference. Been there and done that with Bob. 0.2 compression difference doesn't give 10HP increase.

 

Anyway, there is a way to get the open chamber run as good, better, or close to close chamber head and that's giving the spark better flame front. I think MSD box helps that. I read 5% HP gain.

[Lockjaw]

Geez man, even Bob agree'd with me.

 

On the premise that I am allowed to run gas out of a pump from my local amoco station, I may take you up on your challenge.

 

What about headwork? What is allowed versus what is disallowed?

 

What about the engine? Does it have to be 2.8 liters, or can it be any sized L6 up to 3.1 L?

 

BTW, what does an 8.40 in the 1/8th work out to in the quarter mile? Using the 1.57 factor I have always heard produces a 13.2, and that was a stock engine with an unported head. P79 head.

 

Yeah I know the conversion is sort of bench racing and all that, but we did not have a quartermile track around us then.

 

There are a lot of variables. What about transmissions and rear end gearing. I have to know this stuff, because I don't want to be accused of cheating, and I will say I subscribe to the Smokey Yunick method of determining what is allowed, if it doesn't specifically say I can't do it, then it must be ok.

 

Any camshaft limitations? How long does the motor have to last? Does it have to be streetable? Use Carbs? Etc.

 

The only thing that sucks about this is it will distract me from playing with my turbo car, and nothing I do to the NA engine will make it as stout as more boost on the turbo.

 

I need a partner in crime, anybody game? Maybe I need to check with my pal Ira and see what he thinks. This could be fun.

 

And Dan, I love you too, we just disagree on this particular subject. Oh and my eye's are brown.

[SleeperZ]

Originally posted by yo2001:

Dan, there is a hard number from the factory. The late zx motor with P series head produced 10 crank HP more than earlier zx with N series head. And don't say it's because of the compression difference. Been there and done that with Bob. 0.2 compression difference doesn't give 10HP increase.

 

Anyway, there is a way to get the open chamber run as good, better, or close to close chamber head and that's giving the spark better flame front. I think MSD box helps that. I read 5% HP gain.

Seems to me there are MANY variables that can account for this difference, and unless you are running 10:1 compression, I can't believe head design, excepting port flow differences, could make any difference whatsoever. Just questioning though, as I've never run a high compression L6.

[Dan Baldwin]

Yo,

Like SleeperZ said, there are a lot of things that go into factory hp ratings. Many times they change from one year to the next with NO engine or exhaust changes. Also, a 0.2 difference in compression on a 140hp engine could mean as much as 3hp. I DO have an MSD box in my car, but the motor ran fine and made good power before the MSD.

 

Lockjaw,

I'm 5'11", 160 lb., dark hair, icy blue eyes.... whoa, wait a minute.

Ahem.

No way we could have two cars identical save for the cylinder head. There's just WAY too much going on that would have a bigger impact on performance than the N42 vs. P-series chamber. I believe the difference would be SO small, that the only valid test would be on an engine dyno. One engine, one ignition system, one cam, exhaust, etc. Two cylinder heads, cc'd to be the same within .2cc. And identical valve events and timing would also have to be ensured. I don't see that happening any time soon. Bulding a P79- or P90-head engine similar to known N42-headed engines will likely only prove that the performance is similar. But performance differences either way, unless really drastic, wouldn't prove one head superior to the other.

 

Again, I'm not out to say the N42 is inherently better, I CAN'T say that since I don't have enough evidence. I don't really believe it, either. It IS, however, a much more straightforward issue to plop an N42 on an F54 bottom end to get a 9.8:1 motor than it is with a P-series head. Which is why I recommend the N42.

 

What I cannot fathom is why you would continue to say that the P-series is the ONLY choice in the face of documented performance from N42-headed motors. WHY do you think the Ps are so much better? WHERE are the 235rwhp, 320flywheelhp, sub-13sec P-head cars?

 

Anyway, I'm not much of a street- or dragracer, but when I get my Z back down south I'd be glad to run ya, win or lose. Better yet, we could go to Little Talledega. Cut my roadracin' teeth there, heh, heh.

[Mikelly]

This is actually a good topic... I spoke at length with the folks at Malvern Racing and at Zdr. about this setup years back. Malvern Racing actually HAS (Or had at the time) flow bench data on the heads. Out of the box the N42 is by far the SIMPLE solution. However, if you are prepared to spend the money to have the P90 (Mechanical) head shaved .080 and then shim the cam towers, acquire the proper lash pads, and do the setup, then the P90 is the BEST flowing american head produced for the L series motor. THAT is a BIG However...and expensive too!

 

For what it is worth, the L6 motor I built years back that made 240+HP was using a N42 head with Big valves cut into it and some porting...

[240Z Turbo]

Although I run the P90 I would probably do a big valve E30 or an N42 the next go around. Did you think about the fact that the valves on the P90 are sunk in .080" and never clear the combustion chamber? An E30 or E31 will clear the combustion chamber into the cylinder bore giving the air a 360deg flow path coming out/into the valve. The P90 sends charge right into the side of the combustion chamber. You can unshroud to reduce this effect. Also, the smaller combustion chambers will help to promote turbulence with a tighter squish area. Just my opinion.

[johnc]

The only valid comparison is stock for stock. Once you get out the CNC mills, the carbide bits, the flow benches, etc. all bets are off. There's too much variability.

 

Both are good head designs and a properly modified high performance L6 will make lots of power with either head. Any differences in power have more to do with builder variation then any inherent "betterness."

 

But, no one will listen to that arguement so... I return you now to the group engineering masturbation thing still in progress. Aren't you guys a bit chafed by now?

[Lockjaw]

You gonna run an E31 or N42 on your turbo engine?

 

I forsee a huge "KABOOM" in your future my friend.

 

OK I will give you that for the mechanically challenged, an N42 would be the simpliest choice.

 

But, see all the developement work by electromotive on the L series ceased when the VG engines came out, so they never really got to play with either P series head. Had they, I think you would find they would have surpassed what the N series heads did.

 

James, we are only talking about 2 mm difference on the valve length, and I know when I was setting my cam up in my p79 that is was protruding well beyond the rim of the combustion chamber and I had to get the head up off the bench to finish installing rocker arms. I also think it head was designed that way to make the mixture come out and "swirl" which is where the P series heads are vastly superior to the other designs. Not to mention the P series heads are much more detonation proof than the open chamber N series.

 

Also for you guys, if you recall, the valves out of the N42 head can be put in the P series and you just shim the springs up two mm, and then you maintain your valve geometry. That is what the Z doc guys were doing. Yes it is a little more expensive, but if you already have the N42 and pick up a P series for a hundred bucks, you are set, except for buying the shims.

 

I don't understand why everyone thinks that getting the geometry right on the camshaft is so hard to do. It is really very simple. At least I think so.

 

Now I have 3 people on my side.

[Lockjaw]

Heh Heh Heh He said masturbation.

[Dan Baldwin]

And so the circle jerk continues...

 

For the mechanically-challenged OR for the expert engine builder, the N42 is the simplest choice. More time/effort for little to no gain just doesn't make much sense, no matter HOW mechanically skilled you are.

 

IF the P-series heads ARE superior due to their flow swirliness, I still doubt that they're VASTLY superior in terms of absolute power production, if at all.

 

As for the Ps being "much more detonation-proof", the ONLY times I ever noted any detonation in my motor was:

1) WAY back in '95 when it went in the car, 3.1 liter, ~10.2+:1 CR, lightly shaved but otherwise unmodified N42 head, stock N42 cam, stock 240 carbs. I STUPIDLY tried to run it at 18 degrees initial advance with the stock distributor, which would've given me ~43 deg total advance. It did ping, so I backed it down to 10 initial, which was where it shoulda been to give 35 max advance, anyway. No pinging or other issues for 6 years, ~25,000 miles, and maybe 30 or so track days.

2) I got some run-on/dieseling last year and some minor low rpm high load pinging. Turned out I was missing an advance weight spring, giving me 23 - 28 or so degrees advance at idle and low rpm. Before I discovered the missing spring I discovered that Bardahl's "Knock-Out" does a good job of eliminating dieseling and pinging, if nothing else.

 

"Yes it is a little more expensive, but if you already have the N42 and pick up a P series for a hundred bucks, you are set, except for buying the shims."

 

I'd say if you already have a good N42, you're ALREADY SET! No shaving, no shimming, no head-hunting and buying, no futzin' around, no nuthin'!

 

Lockjaw has three people on his side, and I've got three different N42 engines with documented chassis dyno, engine dyno, and 1/4 mile results. 235 rwhp 3.1 na street motor, 320 flywheel hp (correct me if I'm wrong here, somebody) 3.0 na race motor, and 12.88 sec at 106mph 2.9 na street motor. Who ya gonna believe?! I know this does NOT prove the N42 better than the P-heads. Surely it at LEAST proves them worthy of consideration in performance L6 applications.

 

OK, now I'm chafed. FWIW, don't try motor oil for more personal lubrication purposes.

[Lockjaw]

So what are you trying to say, exactly ?

 

Damn, now I am going to have to come up with a co-helper to prove this point. I don't see what is so tough about somebody making a concession that perhaps the P series could be better.

 

Why would Nissan make a change, and make it for the worst? How hard would it have been for them to just make the combustion chamber a little bigger on the N42, and use the same dished piston as in an N42 block, and turbo it?

 

Why did they feel the need to completely redesign the heads?

 

Dan I am not belittling what you have accomplished with what you have done either. I think the power outputs you are getting are impressive, and there may not be huge differences between the N and P series, but if there is a 10 hp difference, to me, on an NA engine making 235 hp to the wheels, that is significant.

 

Also, if you will note, all of the high performance aftermarket heads now use the smaller closed combustion chamber.

[yo2001]

Originally posted by Dan Baldwin:

Yo,

Like SleeperZ said, there are a lot of things that go into factory hp ratings. Many times they change from one year to the next with NO engine or exhaust changes. Also, a 0.2 difference in compression on a 140hp engine could mean as much as 3hp. I DO have an MSD box in my car, but the motor ran fine and made good power before the MSD.

Why are you arguing? between late zx and early zx, late zx produced 10HP HP at the crank. In stock conditions. So are you saying the Nissan deside to rate the late zx different from earlier one? That would be wierd. Like you said, the 0.2 did not add 10HP to the later zx.