whats better p90 or n42 head

[Bob_H]

Ok, I lied, I am weighing in again, but only b/c someone new posted.

Z speed auto. There appears to be several inaccuracies or poorly worded info. Time to correct:

 

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

Uhhh. Square exhaust ports with the Maxima head? The N-47 by definition is a exhaust liner head. I.E. round. I assume by "Max head" you mean the Maxima N-47 with its associated small combustion chamber. Am I missing something here?

 

but you must frist change the valves the stock N47 "Max head" has small vales

Actually, you only need to change one of the valves. Off hand I forget if it is the intake or exhaust which is the "smaller" size. The other is the same as the regular N-47/42. And as a side note, when you have the choice of only enlarging one valve? Which one would you enlarge? There's a question for you John...

 

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$$$

 

Well, that ignores one rather important part. The PRIMARY reason it would produce more power is the signifiantly higher Compression Ratio vs. the N-42. There are many advantages of the "Maxima head" and many shortcomings.

 

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.

I call BS. First, are we talking no mods? Of course it will have less power. Again, say it with me folks: compression. However power line smoother? I don't buy it. Give me some cold hard facts as to why it would have a "smoother",(which is a totally subjective term), power line/curve? No anctedotal evidence of My car ran better than X car. Your profile says you own a shop, but we need a higher standard of proof here.

 

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

And why not the N-42 as Dan has with 230+ hp at the rear wheels? I only have 180 with my 3.1L and P-90A. I think a better statement would be: "To really get the advantage of the P-90, you need a turbo motor".

 

And as for your question about the same cast? My take on it is as thus: (just my opinion, based on absolutely nothing), They just altered the mold as things progressed. If you look at the evolution, one or two things changed each time. A bigger valve, a larger combustion chamber, the other valve got bigger, a slightly reshaped combustion chamber, an exhaust liner with redesigned intake runner, same runners with new chamber, and old exhaust with everything else the same. The legend for my little history lesson is as such: E-31, E-88, E-88, N-42, N-47, P-79, P-90.

-Bob

[SleeperZ]

Hehe, that's a wrap folks. Seal it up and dump it into the Pacific now.

 

Always a fun topic - I enjoyed the first, and this one was nearly as entertaining. Good info, no name calling or bruised egos. Now on to cam shaft discussion.....uhhhh, maybe not

 

[Lockjaw]

I can do cams too.

[johnc]

Sorry LJ,

 

Jeffp and 240Z Turbo are in charge of the cam threads.

[Lockjaw]

Tim the detonation resistance comes from the design of the combustion chamber, and since I am not an engineer, I cannot elaborate much beyond that. The Z doc boys gave us the run down on that years ago.

 

I think the closed combustion chamber with a high swirl design is better than the open design of the N42.

 

One of the things we noticed when we were some head swapping fools a long time ago was that heads like the E88, particularily when used on my pals 3 liter with rolled dome venolia's was that there were places on the top of the piston that were silver, as though there was no burn over there. However when swapped to the P79, the tops of the pistons were much more evenly covered.

 

What we ASSUMED (yeah I know) was that the P79 for some reason offered a more complete burn, and hence that is where the power increase cam from.

 

Now I am not an engineer, so I can't get into all the theory and stuff. I can understand it if someone else does though.

 

Anyway, we also surmised that since the combustion chamber was designed to swirl the incoming mixture that the P series allowed a more even and complete burn. That also contributed to the detonation resistence.

 

Bob did touch on the detonation resistence issue, although I don't recall if he stated why.

[Lockjaw]

I got clarification from my pal, my buddies 240 with a 2.8 and milled P79 ran an 8.42 in the 1/8th. That is within 1 tenth of a second of what Norm just posted he ran at the strip last night, so I would say his car was fairly stout. Of course that was about 10 years ago.

[TimZ]

Originally posted by Lockjaw:

One of the things we noticed when we were some head swapping fools a long time ago was that heads like the E88, particularily when used on my pals 3 liter with rolled dome venolia's was that there were places on the top of the piston that were silver, as though there was no burn over there. However when swapped to the P79, the tops of the pistons were much more evenly covered.

 

Once again, this could have been due to any number of factors. It could have been as simple as the shape of the dome, and the way it matched the shape of the combustion chamber.

 

Turbo cars do not run domed pistons.

 

At least mine doesn't.

 

My guess is that the 'detonation-proof-ness' factor came simply from the lower compression afforded by the larger chamber volume.

 

One additional thing, just to muddy the waters further, is that the closed chamber design also leaves the edge of the chamber exposed, since it is smaller than the bore size, where the open chamber does not. Sharp edges are bad for detonation.

[Guest Anonymous]

I think a trip to the junkyard is in order here.

First thing you will find before even taking anything off, is there is a block off plate behind the power steering pump for a mechanical fuel pump.

Next thing you will find, upon taking the exhaust manifold off, is no exhuast liners. Unlike the 280 N47.

Upon unbolting the head, you will find this head far more resembles a P90 than an N47.

And you just may be shocked to see, both valves are smaller.

So, its truly not the N47 found on a 280.

 

My previous post was only triying to point out, the dollar for dollar difference on building or chosing heads for an L28.

 

I know my spelling and English and grammar sucks, need you try and figure this out? I spend most of my time arguing with machines.

 

[Lockjaw]

Hey what do I know anyway? I am just a shade tree saturday afternoon tinker with it kind of mechanic. I can't explain the how come's and why's,

 

I just know what has worked for me and my friends. Over the years we have found that we have had way more success making an inline 6 datsun engine go fast with the P79 or P90. Every engine we have ever put an N42 style combustion chamber head (E88) on a car has run awful in comparison to the P79. The E31 style E88's typically ran much better for us, but not as good as the P79.

 

Now I am going to have to look into this maxima head thing, but dadgumit, if I go that route, I am going to have to get my exhaust redone, since my current header is a round port one, but I have a square port one. Maybe I will mill the Maxima head some and see what happens.

[Bob_H]

Off to Beaver Run for the weekend so this is quick.

It has been over three years since I last saw a Maxima head, and time blurs the memory, so I will defer to you and DAW on exactly what is on it as I am sure the two of you have some more recent experience than I,(and I never disputed the fuel pump, my P-90A has the block off plate as well).

I had no problem with your spelling,(mine sucks), but I said poorly worded because it wasn't clear. Grammar wasn't really an issue.

I myself had mAdz GraMmer sKiLz! So I'll be the last to call someone on that.

-off to the races,

Bob

[Dan Baldwin]

I would respectfully submit that there MAY be more of a difference between the E88 (of which there are FOUR distinct varieties) and the N42 (not saying either is better or worse). The '71 E88 has E31 chambers, and reportedly the best-flowing runners of any L-series head (source: D.L. Potter's answer to a letter in an old ZCar Mag). The '72 E88 has a larger, open chamber. The '73 E88 has a much larger chamber than the '72, and the '74 260Z E88 has the '73 chamber AND a larger (280Z-sized) exhaust valve. The '73 and '74 E88s are regarded as "emissions" heads, and are avoided. Which may or may not mean anything. N42's had very slightly smaller chamber than the '72 E88, and BOTH valves are larger.

 

As far as "detonation-proof-ness" goes, both TimZ and myself have reported NO detonation problems. Speaking for myself, that was with an unmodified (save for some shaving) N42, at 10.2+:1 CR, with advance 2deg beyond the optimum for peak power (fixed that at the dyno). After the head mods (porting and slight chamber work), I ran at 5 deg. over optimum advance (even did one dyno run at 7 deg. over) and still had no problems other than reduced power.

 

We have run ACTUAL N42 heads (not supposedly N42-chamber E88 heads), and not had problems with detonation.

 

LJ, did the E88 heads you've had experience with have the stock, smaller valve(s)? If so, obviously they would perform differently from an N42. If not, WHO did the bigger valve transplantation? Do you KNOW what year E88s you've used (aside from the E31-style which is obviously a '71)?

 

Also, as long as you're willing to try the Maxima N47, why would you still be unwilling to try an N42, which you STILL have no direct experience with? Probably for the same reasons I'm not going to try a P79 or P90 anytime soon. It's likely not worth the effort for either of us.

[Lockjaw]

Well 2 of the E88's I tried were the E31 style, and they rocked. One was a MSA head, and of course I imagine it was milled, and the valves were unshrouded. Not sure about the valve sizes. The other E31 style was the one that came off my buddies car that ran the 8.42. It came on the 2.4 his car came with, and it was also milled and unshrouded.

 

The one we ran that sucked was one I got off a 260 I bought ( or it oculd have come off my original 2.4, not sure ), and if I remember correctly, it had the bigger exhaust valves, not sure about the intakes. I took it down and had a nice 3 angle put on it, and had it milled 30 thous, and it never ran good. Let me qualify that. It ran good, just not as good as the milled P79's. It was the open chamber design, unlike the E31, and I talked with some guy out at Nissan Motorsports about milling it, and he told me not to, so I was very conservative and should have milled it more.

 

Of course I get into conversations alot with people who "know" Z's, and when I say something about an E88 head with E31 style chambers, they freak and call me a liar and such, and if I recall, the guy out at NISMO did not know what I was talking about either. I kept telling him, no this thing has a big combustion chamber.

 

Anyway, the machinist said this head had the hardest seats he had ever encountered. Whatever that means. They were not steel I know that much.

 

As far as an N42, I would try one if I got into one cheap, and if I go the maxima head route, I will have to come up with one to get the valves out of it anyway.

 

That said though, I just don't have faith in the fact that the open combustion chamber is going to do what the closed one will.

 

Plus we are also adding some expense to the mix because I am going to have to buy two heads, and swap all this crap out, add valve stem seals, and then of course buy gaskets and perhaps have valve jobs done.

 

I am working on my buddy right now to put his engine together which will be a 40 over flat top engine with a P90 and the same crower cam that my buddy ran along with the same webbers, so that could have some potential as well. Of course the webbers need a rebuild by now I am sure, and they are still on that sucky Cannon intake (according to Top End).

 

But no I would not be unwilling to try one, but the Maxima head now has me intrigued. I have an email into a friend to see if he has one laying around, if not, I guess I will mill another P79 because I am just not happy with the one that is on my car and it does not look like it has been milled, yet is mic's out as having material removed. I guess it could have come off the top of the head. I am just not sure what the heck the machine shop did with it, and I don't think I am getting the cranking compression I should be getting either.

 

Let me see what I come up with.

[DAW]

I'll try to take some photos if someone will accept an e-mail attachment and post them as I have no website set up. Photos of combustion chambers of E31, early E88, late E88, N42/47 280Z, N47 Maxima, and P79.

 

It's difficult to equitably compare heads unless you're using a head with the same cc and valve size as the comparison head and the cam/setup is the same and they are both tried on the same shortblock. It's no surprise that a shaved P79 would out perform an E88 of an equivilent cc if the valves in the E88 had been changed to be as large as the P79 (44mm/35mm). Apples and oranges.

 

Perhaps the most equivilent comparison of the two chamber types would be between an E31 with L28 ex valves installed, and an N47 Maxima with 240Z cam (and oiler bar towers) and intake springs; these would go onto an L26 (flat-top) shortblock for a c.r. of about 9.5:1 (ballpark). These heads have cc's about the same and would have 42mm/35mm valves and same valvetrains once setup as above but the big difference is that they have different chamber configurations (and sq vs rnd ex ports). The parameter that's important to me is if one head allows detonation more easily than the other at a given fuel octane and timing setting (and mixture). If they produce the same power at conservative settings but one allows me to further advance timing for throttle response, power, and mpg where the other can't due to ping...then in my mind the less ping-prone head is the better all around choice for stock, hi-perf n.a., or turbo use (as it will allow more boost without detonation and ECU-mediated timing retards). My gut feeling from similar exercises with U67 (open) vs W53 (closed) L4 heads is that the closed chamber has the edge at the same c.r. However, to duplicate the c.r. the open chamber head has to be on a larger displacement shortblock so it's apples and oranges as is the case comparing an N42 to a P90 (unless it's a P90 that's been cut & shimmed to be the same cc as N42). The E31 (or early E88) vs Max N47 set up as equivilents is the closest/fairest comparison of the two chamber types.

 

BTW, if I get these pics I'll include one of the port-flange side of an L28ET turbo ex manifold. I'm thinking it could be used on a round-port head (liners removed of course; PITA but not that big of a deal). I have a square-port N47 head on one of my engines which probably came from a JDM used crate motor. So there are N47s with totally different chamber types and port types and the common denominator seems to be cam tower-oiling, vs the spraybar-oiling of the N42. DAW

[Dan Baldwin]

Hey, NOW we're getting somewhere! Quick E88 review:

1971: 42mm in, 33mm exh, E31 chambers, 42.4cc, generally highly regarded

1972: 42mm in, 33mm exh, open chambers, 44.7cc, well regarded

1973: 42mm in, 33mm exh, bigger chambers, 47.8cc, poorly regarded emissions head

1974: 42mm in, 35mm exh, 47.8cc, poorly regarded emissions head

 

Lockjaw:

"Well 2 of the E88's I tried were the E31 style, and they rocked."

 

OK, that's the head that was praised by a recognized expert in the field. Closed combustion chamber, and small valves, so not much like an N42. Not a whole lot like a P90 either, I guess.

 

"The one we ran that sucked was one I got off a 260 I bought ( or it oculd have come off my original 2.4, not sure ), and if I remember correctly, it had the bigger exhaust valves, not sure about the intakes."

 

Ah-HAH. Sounds like the 260Z E88. Generally avoided, and nothing to do with an N42.

 

" I took it down and had a nice 3 angle put on it, and had it milled 30 thous, and it never ran good. Let me qualify that. It ran good, just not as good as the milled P79's. It was the open chamber design, unlike the E31, and I talked with some guy out at Nissan Motorsports about milling it, and he told me not to, so I was very conservative and should have milled it more. "

 

Yeah, your CR was probably lower than you or he thought.

 

"Of course I get into conversations alot with people who "know" Z's, and when I say something about an E88 head with E31 style chambers, they freak and call me a liar and such,"

 

My 8/71 car HAD that head on it. Long gone, now. Seems to me that the fact that there are FOUR different E88 heads, along with the assumption that the N42 is pretty much the same as an E88, might have led to some poorly-drawn conclusions on your part. Don't see why you would attribute your better performance with the P-heads to bigger valves as much as to combustion chamber design, as the "good" E88s all had smaller intakes and exhausts. Definitely sounds like your one(?) poor experience with an E88 was with one of the "bad" ones. (note the use of quotes, as I have no direct knowledge whether those heads are really "bad" or not)

[Lockjaw]

Dan the main reason I am not so hung up on the valve size was because of the guys 240 which ran an 8.42 . He started off with his good E88, and his car was strong with that. In fact he blew the head gasket racing against a P79 equipped one. I was in that car.

 

HE swapped the E88 for a P79, and yes it improved, but he also stuck this nice big crower cam, althoug the size difference could not be as great as we initially thought.

 

Anyway, his E88 was not to far off the other guys P79, but the P79 on that guys car was only cut 45 thous. Tom had his cut 110 thous. We kind of felt the compression bump helped more than the larger valves in our twisted little minds.

 

You have to put alot of what I am saying into perspective too. This happened about 10 years ago, and we got hot and heavy into putting the stock turbo engines over in our cars, and everyone of us has moved on from there. Alot of what I would consider now would not have crossed my mind back then. In fact it has been so long it frustrates me to fire up my car with SU's and have to blip the throttle a little, or always have to choke it. Know what I mean?

 

Besides I was only about 22-24 during this time period, and I am 35 now, so I think that helps for me, I have gained another 10 plus years of experience.

 

Alot of what I have learned about this sort of thing has been thru working with JWT on getting the ECU dialed in on my turbo car. Clark is a patient guy, and he explained alot of things to me that I would not have understood otherwise. PLus my co-conspirator in all this is a mechanic by trade, so he helped to.

 

We did insane stuff back then to. It was nothing for me to go swap a head, a diff, a trans. Now it is an act of congress. We could swap engines in less than a day. Now it takes me a good day just to get the freakin' turbo off my ZX.

 

We actually were going to run an N42 back then because it had the big valves and the square exhaust ports, which was what all the nissan hotrodding literature said was the ticket. Then that guy comes in with the P79, and I am totally serious when say this, one ride was all it took to send the rest of us out on a shopping spree for a flat top 280 engine and a P79. We were in constant one-up-manship during that time, and were always buying some part and sneakily putting it to use.

 

I had lots of fun with that car too. I had a kid with a turbo probe that could beat me with the 2.4, and he could run me down with a 2.6, but I could kill him off the line. With the 2.8 and a P79, I jumped that sucker from a dead stop and never looked back. He could not believe it.

 

I probably drove that car in a manner which would make Norm proud. It had a light HKS flywheel, and I would sit beside someone holding the rpm's at 5k, and when the starter dropped his hands, man it was full throttle and dropping the clutch.

 

I found out early on that the secret to making these NA 240Z's spank on someone was to rev them way up and dump the clutch and hang on. Yeah they spun, but they motivated while doing it. I beat more people out of the hole then.

 

Sorry to digress. Anyway, we were going to try one, just never did. The P79 dude came to town and ruined us.

 

Oh and it looks like I had one of the sucky E88's too.

[Guest norm[T12SDSUD]]

Might as well throw my log on the fire!

 

My N42 is shaved .070" which basically turns it into a closed chamber design with a 35.1 cc chamber.

 

SO I guess I have a homemade PN42 head! hahaha

 

The best head to use simply depends on the intended APPLICATION!!

 

The CR and cam is way more important to making power than whatever minor flow characteristics each head has since the runners are so similiar.

 

Later,norm

[Lockjaw]

Norm

[yo2001]

Norm, that's what I basically runs. E88 with .080" shaved It's not like P series, it's more like E31. A semi-close chamber. Well, at least my head look like that.

[Guest Anonymous]

Thank You Norm thats what i was trying to say.

 

"The best head to use simply depends on the intended APPLICATION!!"

 

and $$$$ has to play in there some place

 

maybe i should of just gone off and started talking about how P.C.P controlls H.P.

and how P.C.P is influenced buy timing, gas, the cc of the head as well as shape, the piston shape, size of the bore and stroke,compression, and how the air and gas gets in the motor,

 

as well as if P.C.P happens to late the motor works agenst itself

if it hapens too, soon it does not make the power it can, and to get the P.C.P to happen when you need it,depends on what you are doing

 

and for he who says a P90 on a stock F54 block makes less power and runs smother than a N42

is BS? this is the proof on the how's and why's

(Note the P.C.P hapens to soon on a na motor thats stock with a P90 stock)

 

P.C.P = peak cylinder pressure

 

hey Norm, Ken J should have the 3.1 back up and running soon

[Bob_H]

Crap, see what happens when you go off and race?

Ok, DAW, you said Round ports for the Maxima head. Z sport auto, you said square? Do we have a concensus? And I want to point out the variance in your posts:

First:

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,

So we have square ports. Then:

Next thing you will find, upon taking the exhaust manifold off, is no exhuast liners. Unlike the 280 N47.

Ok, no liners, but are you now saying it is round? Then DAW said in discussing the difference btw an E-31 with big valves and a Maxima N-47:

above but the big difference is that they have different chamber configurations (and sq vs rnd ex ports).

So now we have round ports. DAW, liners or not? I am ignoring the one odd square port N-47 you mentioned. I too have seen a 280z(edit 280zx turbo, may bad) N-47 with square exhaust ports, but only one.

And to clarify on the P-90 power and being smooth. You said:

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 which I responded:

I call BS. First, are we talking no mods? Of course it will have less power. Again, say it with me folks: compression. However power line smoother? I don't buy it. Give me some cold hard facts as to why it would have a "smoother",(which is a totally subjective term), power line/curve?

Now, the last quote, your last post:

and for he who says a P90 on a stock F54 block makes less power and runs smother than a N42

is BS? this is the proof on the how's and why's

(Note the P.C.P hapens to soon on a na motor thats stock with a P90 stock

First, I never disputed the less power issue. But I contended it is because of COMPRESSION. Peak cylinder pressure is a function of compression, so if that is what you mean, we are talking about the same thing, you are talking about the effect, I am talking about the cause. However, that has nothing to do with the power line being smoother by my definition,(again, a subjective term, please define what you mean by smoother). Bottom line, the PCP is lower because of the lower compression. I am ignoring the effects of timing, rod ratio, etc.. On two identical motors, lets say a stock flat top 2.8, one with the P-90, one with the N42/47, the P-90 has less power beacuse of the significantly lower compression. An effect of that lower compression is the lower PCP value. If you are equating lower power to a smoother line, ok, but that is the first time I have heard it refered to in that way.

So to sumarize:

Looking for clarification from DAW and Zspeedauto as to square vs round. My contention was round,(with liners, but I can't remember 100% on that). Next, looking for a definition of what a "smoother" power line is. For I take it to mean less peaks and valleys, i.e. similar to what you see on a hp curve from a motor with detonation vs. one without.

And I am glad to see Ken is about to get back on the road. I talked to him last week about his supercharger plans. I think you guys are nuts and he can't keep well enough alone. But he has turned me on to check out Perfect power and their PRS-8.

-Bob