whats better p90 or n42 head

[yo2001]

Anyway, the point is either way you go, P or N, the HP is going to be about same. Dan, we can't compared your N42 head and stock P head.

 

BTW, I run shaved .080" E88 with N47 valves. Which is like large valve E31. (semi-open chamber) 10.3:1 with small conpared with Dan's cam , on dishtop pistons.

[johnc]

> 320 flywheel hp (correct me if I'm wrong here,

> somebody)

 

Dan,

 

If this refers to my engine, its 305hp at the flywheel. If its someone else's motor, I'd like to hear more.

[Dan Baldwin]

Lockjaw:

"I don't see what is so tough about somebody making a concession that perhaps the P series could be better."

 

I've conceded just that on a number of occasions. Key words being "perhaps" and "could be".

 

"Why would Nissan make a change, and make it for the worst?"

 

1970-1972 240Z. 1973 240Z/1974 260Z. Why indeed would Nissan make a change for the worse? Sometimes it happens anyway. BUT, I'm not saying the P-heads ARE worse.

 

"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?"

 

I dunno.

 

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

 

Why not? I'm sure the redesign attempted to address more issues than outright maximum performance. As far as I know, it could've been for reduced emissions or improved fuel economy, something I don't think too many of us are all that concerned with. I'm not saying that's the case, just a possibility.

 

"I think the power outputs you are getting are impressive, and there may not be huge differences between the N and P series"

 

That's what I'm thinking.

 

"but if there is a 10 hp difference, to me, on an NA engine making 235 hp to the wheels, that is significant."

 

Again, I agree 100%. 10 hp IS significant. I just don't believe there IS that much between them, particularly if they've been modified. Which, at that hp level, surely they will have been. I could be wrong, there *could* be an inherent 10hp advantage to the P-heads. Or there could be an advantage with the N42. I just haven't seen any conclusive OR reasonable anecdotal evidence one way or the other.

 

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

 

Proving...

 

Yo2001:

"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. "

 

"Weird" happens all the time with automobile manufacturers. Maybe the marketers felt like they needed 10 more hp that year. Maybe they really DID make +10 hp, or more. I agree that 0.2 cr difference likely doesn't amount to 10 net hp. Real hp gains, if any, between the N42-head N42 motor and P79-head F54 motor could as easily be attributed to flat vs. dished pistons as to P- vs. N-combustion chambers, though. Not saying that's the case, just that it COULD be.

 

Hell, I don't know. I just don't think you guys do either

[Dan Baldwin]

Thanks, John. I stand corrected, that's 305 flywheel hp. Somewhere I'd heard "way over 300", and somewhere I actually saw "320". Now I know your lame-ass motor is only making 305. You probably don't even have to use the brakes! O' course me, I can only barely beat a fricking Omni!

[yo2001]

Originally posted by Dan Baldwin:

Hell, I don't know. I just don't think you guys do either

Me either This subject should be locked in a sealed box and throw into the Pacific ocean

[DAW]

Not to play devil's advocate, but the hp increase in the ZX vs Z L28E is associated with a 0.5:1 increase in compression, not 0.2:1 (8.8 vs 8.3:1 c.r.). There's a rule of thumb re expected hp/c.r. change which I don't have in front of me but .5 is not insignificant and can be felt in the seat of the pants dyno.

 

I've found the N42 to ping on a 10:1 2800cc with 86x79 engine but not on a 10:1 2800cc with 84.5x83. There's probably a good explanation for that re piston speed around TDC with regard to stroke length and rod/stroke in the 130.4/79 engine vs the 140/83 engine. I'm thinking about low-pressure turbo for the 10:1 engine that doesn't ping for the next step up in performance since I've never heard it ping using premium gas.

 

Another option would be to increase the c.r. over 10:1 by putting on a head with smaller chamber volume than the N42 such as an E31 or early E88, a severely shaved/shimmed/lashed or Z-valved P90/79...or, the best choice re cost, f.i. provisions, minimal prep work, closed chamber...the N47 Maxima head with 280Z intake valves/seats, springs and cam.

 

Not many people on this site have really explored the use of this head. Granted it has round exhaust ports vs square but it looks to me like a turbo exhaust manifold can bolt to either type of head. This is a totally different head than the 280Z N47 head, even though they share the same casting #. There is a possibility that this head was used on JDM L24s and had square ports. I think the emmission laws which dictate the liners may be different in other countries as I've seen P90s on Japanese n.a. L28s. The Maxima N47 comes on the U.S. L24 with slightly dished pistons (maybe 2-3cc) and a c.r. of 8.6:1. This means it has the chamber volume approximately that of an E31 but the configuration of a P90/79.

 

Comments are welcome. I ask only that you have personally seen the chambers of an N47 Maxima before you comment. Please don't discourage beginning builders by speaking negatively about something you're purely speculating on. I don't want to sound preachy but several years ago I was told by many "experts" including NISMO techs that I couldn't put together a long-rod stroker using an LD28 shortblock and L28 top-end. Turns out they were wrong and they were speculating rather than speaking from experience. (I've been driving the car for years now and it performs well and is very reliable). DAW

[Lockjaw]

Daw I neglected to deal with that head you mentioned, but I have thought about it. It seems to me like it would be worth a shot if not for anything else, then to simplify the process for techically challenged folks.

 

Dan, have you ever actually run a P series head? Serioulsy, have you every gone to the trouble to mill one, shim it, and put it on a car?

 

I have run just about every head out there, except the N47 and N42 ( although I used an E88 with the same combustion chamber as the N42. I went from a P79 to an E88 and lost power on a flat top 280ZX bottom end. Nothing changed but the head, and I had the E 88 milled 30 thousandths to boot. My buddy went from an E88 to an uncut P79 on his high compression 3 liter, and picked up power. My other friend went from a seriously milled E88 with the E31 style combustion chambers to a cut P79 and picked up power. On all three of these engines, the only thing that was changed was the head.

 

Yeah no hard numbers, but they all ran better. Now I am sure there are variables that can factor into that and make some differences, but the bottom line is on every engine we have done something with, when we went from any series head to a P series, we gained power. We just weren't very scientific about things back then, and to be honest, we did not care as long as it made our cars faster.

 

Bring your Z on down here. I would like to see what it is all about. On a road course, you can have your way with me, but on the strip, that turbo will make you long for some NOS.

 

Now if I put all that over into my 260Z, then you better look out.

 

Dan for what it is worth, I was like you. When my friend who is a pal of the Z doc boys up in VA came in with his "smogged" 2.8 with a p79 on it, and told us the Z doc guys said it was the head to run, we laughed our heads off. We actually got off to the side and made fun of him. He put up with our ribbing for a long time. But when he put the engine in his car, with the head milled a mere 45 thou, and ran a cam I had run in my many different heads that never was spactacular, and took me for a ride, well I was shocked.

 

I raced him that night in my 240. I had a 2.4 with a cam, header, light flywheel and 3 two's, and I never had run across a Z that could handle mine from a low speed kick, but his did. He pulled out on me and kept on going. From that point on, we believed.

 

Dumb story I know. Short of hard numbers from someone, there is no way anyone will ever convince me that the open chamber N42 is superior to a closed chamber P series head.

 

Oh and on the subject of compression ratio's, a full point in compression is supposed to be worth 4 percent more power, so half a point would theoretically be 2 percent. On a 130 hp engine, a half point compression would theoretically bump its output up to a tire shredding 132.6 hp. I believe Yo would be correct that the factory did show an increase of 10 hp going from the N42 to the F54 engine.

 

Just for comparison, a pound of boost is supposed to be worth a 7 percent increase in power. But that is another thread.

[Bob_H]

Oh god, I thought we circle jerked this long ago. I'm gonna weigh in once on this, and that's it.

First, I would bet MY CAR, that if we could get one car, and two identically preped heads,(same cam, event timing, etc..), one being a P-90 and the other being an N-42, that we would see less than a 5 hp difference, or within the region of error.

Where I think the difference/advantage if you want, of the P-series is it "theoretically" protects you from detonation a little longer. Beyond that? We are all guessing.

So more questions, why the P-90 on the turbo and not a N-42 with bigger chambers? And DAW aluded to using a N-47 with the turbo manifold,(I assume to run a turbo?). First, with any round liner head,(steel inserts, or whatever material they are), the exhaust gasses of a turbo motor and the associated higher temperature would be too much for them. Their original "goal" as stated in some literature, was to heat up and burn off some more combustion stuff hopefully creating a cleaner exhaust. Well, you are sticking something in the way of the exhaust with a turbo, and it tends to run a bit hotter,(more gas and air going in for a given cycle). That could prove to be a problem with liners designed to heat up. It has been rumored,(and blocks I have seen supported this), that the very first turbo's had N-42's. They needed a design w/o the liners, and the only existing design was the N-42. The P-90 is a good combination of the slighly sideways D shaped intake ports from the P series, with the square exhaust ports from the N series and the chamber of the P series. Is it the best? I think Nissan took what they needed to make a turbo motor, i.e. put a square exhaust port design in the P-79 head. Name it something new and get on with it. I don't think that means it is the best in the line, but rather the best solution for what Nissan needed at the time.

So please folks, lets not get into the pissing match. Oh, and I know a race motor that produced 315-320 hp at the flywheel with an E-88! So obviously by that logic the E-88 is best.

And Dan, while I admire your argument and for the most part agree, it doesn't hold much weight for what you want to prove: that the N-42 in unmodified form is better than the P-90 or P-79. Because all three of your examples have EXTENSIVE head work. Esp. yours and John's. So by that token, it is only fair to compare an equally prepared P series. Is shaving it equal to porting the heck out of it? Or in John's case, changing the combustion chamber? We all recognize that to compare anything but stock vs stock is unrealistic and proves nothing.

So, with that in mind, here is my opinion:

For 100% stock vs stock, the N-42 is VASTLY more superior,(great gramer skilz eh?). No mods are required to get fairly high compression ratios, which support more power. And that is really the only difference worth comparing stock vs stock.

The only thing I can find in favor of the P-series having an advantage, for "equal" mods if you will is my dyno plots vs other similarly equiped strokers. The get the same hp at the wheels, they were most often running 45 mm carbs and higher compression by about .5 CR. I fully realize there are a million variables, but few motors with my small cam produce 180 to the wheels with less than 10:1 CR. And I think there is another 5 hp to be found if I can ever fabricate a proper heat shield, (DO THIS DAN! I put just a sheet of metal under the carbs when sync'ing them yesterday, wow, what a difference, cool to the touch for the carbs!).

But there I go violating my rule about comparing unequal cars.

So Sean, you enjoying this?

[Lockjaw]

Thanks Bob, I knew you would come around.

 

Oh and I think I am enjoying this every bit as much as Sean, and I like all of you. Now we need to have a group hug.

[Dan Baldwin]

Just answering a few questions. Honest.

 

Lockjaw:

"Dan, have you ever actually run a P series head? Serioulsy, have you every gone to the trouble to mill one, shim it, and put it on a car?"

 

No.

 

"I have run just about every head out there, except the N47 and N42 ( although I used an E88 with the same combustion chamber as the N42."

 

So you have as much N42 experience as I have P-head experience

 

" I went from a P79 to an E88 and lost power on a flat top 280ZX bottom end."

 

Lots of people have bolted on 3X2s and lost power.

 

"Short of hard numbers from someone, there is no way anyone will ever convince me that the open chamber N42 is superior to a closed chamber P series head."

 

I'm not trying to convince you of that. Just that none of us has enough info to say which is better.

 

"Oh and on the subject of compression ratio's, a full point in compression is supposed to be worth 4 percent more power, so half a point would theoretically be 2 percent."

 

I prefer the newhp = (newCR/oldCR formula)*oldhp formula. Probably a bit optimistic, but at least accounts for the fact that half a point from 8.5 is a bigger jump than half a point from 10.5. Anyway, that would be 5hp added to a 140hp engine going from 8.25 to 8.55:1 CR. But who give's a ratsass about those low-comp factory motors, anyway.

 

"I believe Yo would be correct that the factory did show an increase of 10 hp going from the N42 to the F54 engine."

 

FWIW, that's an N47-head dished piston motor to a P79-head flat-top motor. Wonder what if any more inherent power there is in an N42 head vs. N47 (square exh. ports vs. lined round exh. ports). Not to mention (again) that that 10hp is at the brochure.

 

"Just for comparison, a pound of boost is supposed to be worth a 7 percent increase in power. But that is another thread. "

 

That doesn't account for 1 psi being a bigger jump from 8 than it is from 18. Try newhp = (newboost + 14.7/oldboost + 14.7)*oldhp. Optimistic, but isn't that what bench-racing's about?

 

Anyone thinking of taking Bobby up on his bet (his car) should know that his 3.1 has been sold, and I don't think he's taken delivery of the RB26DETT yet. i.e., it's a car w/ no motor!

 

Regarding my cylinder head, it was ported, and some MINOR combustion chamber shaping was done (no material added, of course). I'd be glad to see results of a similar motor with similar work done to a P90, as the combustion chamber comparison would be almost as valid as stock vs. stock.

[Lockjaw]

 

We could do NA cams.

[Drax240z]

Hey guys, I don't have anything really to add here, but I' really enjoying this discussion, and there is some great info here. Glad to see we can still disagree with respect towards each other around here. Kudos.

[Guest Anonymous]

P 90 or N42 its a matter of $$$$

and I'm going to put 1 more head in this the Max of 81 to 83 the N47

its realy a P type head.

All the stuff I'm about to say is with a stock F54 flat top block,

for a straight bolt on the N42 is the way to go.

Just bolt it up and go fast.

With the same cam you will get more power out of a N47 "Max head "it must be a max head it has square exhaust ports,

but you must frist change the valves the stock N47 "Max head" has small vales. You must up size them to the same size as the N42

and this will make more power than JUST bolting up a STOCK N 42

but cost more$$$

 

Now you can bolt up a P90 stock it runs ok, it will NOT have the same power as the other 2 heads BUT the power line is smoother.

To really get what a P90 has to offer your going 3.1 L

 

If you go 3.1 your going to have a TON of $$$$$ into it BUT you will truly get out of it what a 3.1 has to offer.

 

$ for $ the N42 in my book is the way to go

 

Oh, by the way i remember this fight whan it was E31 or N42 way before the P90 was cast

 

and 1 more thing, ALL the the heads P90 N42 N47 "max" and the E31 have the cut out for the fuel pump the 240 uses stock. (the mechanical fuel pump it is not used onany of these heads, other than the E31)

Now THAT's strange.

Is it that all these heads come out of the same cast as the E31?

[yo2001]

If the money is concerned then my $15 E88 beats all.

[Mikelly]

Well again, it all boils down to what parameters you set WHEN bench racing... I know what I was told by folks who produces VERY fast Zcars for a living back in the 90s... I also know that the N42 head worked VERY well for me personally... VERY well!

 

Lets keep it civil guys... Everyone has opinions!

 

Mike

[240Z Turbo]

Lockjaw, since you already paid me for the intercooler I can smack talk you again.

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.

How can you properly debate head choice when you don't even know what you are saying. Shimming the springs will help maintain the correct seat pressure. You need to shim the cam towers and adjust the lash to use the .080" longer valves. It is a horrible way to go, I know because I have the longer SS valves in my P90 head. It creates many problems if you do not shave the head because shimming also affects cam timing. TimZ uses the N42 and makes 431hp&472ft-lbs @wheels on 94octane. Hell, Don Potter also says the earlier heads provide the best platform for making big power on the L6. Blowup my motor with an E30 head????? Only for the lame tuner!

[Guest JAMIE T]

I'm not much of an "Inliner". But guys, I have really enjoyed this thread. Heck, I've got a F54 motor, a L24 with a E31, and a LD28 crank. Maybe I will build me stroker and put the E31 with big valves on it. Second thought, My LT1 runs so darn good with those new heads and HOT cam. 341rwhp, and my wife drives it daily with the AC on. Put it in 6th and just mosey on down the road.

[Lockjaw]

OK you got me on that one James, I forgot the shimming of the cam towers, but if they are shimmed 80 thous, which is the same as the additional valve length, and the springs are shimmed too, then you should not need to change lash pads. So I guess I kind of get to smack talk you back.

 

Dan, if I ran an E88, isn't that the same as an N42 except the N 42 has the slots cut for the injectors? If so, then I have N42 experience by association.

 

I think I have also clearly demonstrated that I have the tuning proficency with webers, so I don't buy your retort about webers slowing down a car in response to my claim of an E88 slowing me down versus a p79, which incidentally had a bent valve, and still outperformed the E88. ( I found out about the valve later ) At least not on my engine, perhaps on someone else's engine.

 

That said, I am going to defer to Bob H's assessment, with one caveat. He has a hydraulic P90A, and I know from personal experience that a P90 head worked better for me on my turbo engine than a P90A. I would bet his car to that a P90 with the same work done to it as his P90A would outperform it. HEHE.

 

Bobs post also reminded me of one other thing the Z doc people were claiming, which was that the P series heads had some work done on them to enhance low lift flow.

 

Anyway, I had enjoyed the debate, and if you haven't figured out by now, I happen to be a touch on the pig headed side. I hope one of these days to see you have finally caved and tried one just to see what the deal is. I am sure you will not be disapointed.

 

You guys are some of the best folks too. Just wanted to let you know.

[Guest Anonymous]

just like to say the E88 has a smaller ext valve

than a N42

by 1 size i think it is

[TimZ]

Man - I tried to warn you guys, but you just couldn't leave it alone...

 

So, if I could recap - after 30-some posts (this time around), we have definitively proven beyond the shadow of a doubt that a highly modified P- or N- series head might, in certain circumstances, make more power than a highly modified N- or P- series head, when installed on the exact same, or possibly a completly different, engine.

 

About this there can be no question.

 

Wow. We are a font of knowledge.

 

I do have one thing new to add/ask - what exactly is the "theory" behind the N42 being more detonation-prone?

 

I run a mildly modified N42 on my car, and this has not been an issue for me.