Newbie seeking advice - what is the best L engine/head combo

[Dan Baldwin]

This was my experience in bolting an E31 onto an L28 with flat tops too. I am beginning to think that our pinging problems have more to do with CA's crap gas then anything else.

 

Huh' date=' maybe. All I can say is I never really had any detonation problems on Georgia, Alabama, Rhode Island, New York state, Pennsylvania, Ontario, West Virginia, yadda yadda yadda gasoline.

 

If Nissan had it "figured out" then why did they bother with the P79? They could have just left it alone and let the N42 go for another 4 years. How come L4 guys all covet the small chamber heads (similar to P90)?

 

If the L4 guys do all covet the small chamber L4 heads, that in itself tells us nothing, even if the L4 heads are perfectly analogous to the L6 heads.

 

I agree with John when he talks about HIS N42. Like when we were arguing this last time and you said that you had your pistons machined to provide quench on your N42.

 

FWIW, MY KA pistons were unmodified for quench, just stock pistons. No probs. Made 235rwhp with approximately 42 track days on that bottom end. Current build does have the pistons machined for valve clearance.

 

Me:

By this logic a 1976 L82 Corvette has MUCH better-performing heads than a 1970 LT-1. Point#1 provides zero support to the P-head performance superiority theory.

 

Dan's argument turns against him here. You're trying to convince us that the '76 head is better than an '81 head. '76 was right in the heart of the crappiest smog years in history, and that's when the N42 came about. Not that '81 was much better, but the '81 certainly looks a hell of a lot more like the '70.

 

The LARGER point was and is, that just because the P79/P90 came a few years AFTER the N42/N47 IN NO WAY PROVES THE P79/P90 TO BE BETTER FOR PERFORMANCE.

 

I am going to adopt Dan's approach on the closed chamber heads though because I like the way it puts the onus on someone else to do something: show me an open chamber L engine that makes the SAME power with flat tops and the same compression ratio as a closed chamber, high quench and I'll be convinced.

 

Again you miss my point completely. For the 1,000,000th time, I'm not arguing that the N-heads are BETTER. I *am* arguing that there is NO EVIDENCE that the P-heads are better.

Get the distinction?

 

But since you brought it up, we really need to see:

1) A P-headed na 2.9 liter ~2300 lb. 240z that runs 12.8s in the 107s on pump gas

2) A P-headed na 3.1 liter that makes 255rwhp on pump gas

3) A p-headed na 3.0 liter that makes 287rwhp/315fwhp on race gas.

before we can consider that the P-heads are even equivalent to the N42, much less BETTER. WHERE ARE THEY?

 

And despite the apparent superiority of the N42 evidenced above, you STILL won't get me to say the N42 is inherently "better". So how come the P-head guys go on about its superiority without ANY such evidence?!

 

Until that happens I'll keep with the engine builders and promote what is commonly considered the preferable design: the closed chamber high quench area head.

 

"preferable" to whom? If 10,000 Z car fans prefer the closed heart-shaped chambers, does that mean they're actually better? If max performance small-block chevy heads have this chamber shape, does that in itself mean that L-series head chambers that *LOOK* like those SBC chambers are necessarily "better" than L-series head chambers that do not?

 

"The sleep of reason produces monsters"

Francisco Goya

[gramercyjam]

Those heart shaped chambers were welded up like that in the "How to modify" book. Monkey see, monkey do. He also had some flat top pistons. They were going for high compression ratio on that motor in the book and that was how that particular motor build got the high compression.

 

Welding up some heads and shaving beyond mfgrs. recommendation are both illegal in the SCCA. If you compete in SCCA, your going to need to find an OEM high compression head, some custom pistons to fill up those low compression chambers, or both. Valve size isn't an issue since you can make the valves and seats as big as will fit on any of the L heads. (All the heads need to deal with the same limiting distance between the intakes and exhausts). Port and polish them. I think it's a wash either way you go. You can make any head work. No, I don't have the tech to back it up. Buy some good race gas to take care of the pinging. And if your not racing, what does it matter really.

 

EDIT: I wonder if there are such as thing as offset valve guides that could allow wider valve spacing ........

[JMortensen]

Again you miss my point completely. For the 1,000,000th time, I'm not arguing that the N-heads are BETTER. I *am* arguing that there is NO EVIDENCE that the P-heads are better.

Get the distinction?

 

Yep, I sure do. I AM arguing that the P heads are better.

 

But since you brought it up, we really need to see:

1) A P-headed na 2.9 liter ~2300 lb. 240z that runs 12.8s in the 107s on pump gas

2) A P-headed na 3.1 liter that makes 255rwhp on pump gas

3) A p-headed na 3.0 liter that makes 287rwhp/315fwhp on race gas.

before we can consider that the P-heads are even equivalent to the N42, much less BETTER. WHERE ARE THEY?

 

I dunno. Swap modded P heads (and pistons on John's) on all those motors and see what happens. I'm not about to try and duplicate all the work in those engines to prove a point to you.

 

And despite the above superiority of the N42 evidenced above, you STILL won't get me to say the N42 is inherently "better". So how come the P-head guys go on about its superiority without ANY such evidence?! ...

 

..."preferable" to whom? If 10,000 Z car fans prefer the closed heart-shaped chambers, does that mean they're actually better? If max performance small-block chevy heads have this chamber shape, does that in itself mean that L-series head chambers that *LOOK* like those SBC chambers are necessarily "better" than L-series head chambers that do not?

 

Evidence:

http://www.federal-mogul.com/cda/content/front/0,2194,2442_897063_6800,00.html

http://www.theoldone.com/archive/quench-area.htm

http://www.speedomotive.com/Building%20Tips.htm

http://www.chevyhiperformance.com/howto/47075/

http://www.beckracing.com/page05.htm

http://www.chevyhiperformance.com/techarticles/94138/

http://www.popularhotrodding.com/tech/0311_phr_power_squeeze/

http://www.atvrideronline.com/quads/100_0308_racer/

http://www.westechperformance.com/pages/Tech_Library/Understanding/hpvstq.html

http://www.moparmusclemagazine.com/techarticles/5115/

http://www.corollaperformance.com/TechInfo/1ZZFE.html

http://www.se-r.net/about/200sx/scc/feb98/february.html

 

I CAN KEEP GOING. I CAN DO PAGES AND PAGES OF THIS.

 

You've got imports, domestics, even ATV's in that list. Everyone seems to think that quench is an extremely beneficial thing, except you Dan. And you won't say that it is NOT beneficial, just that you need proof that it is, and of course the above experts' clear explanations of why quench is important and beneficial don't qualify under your "show me Norm's motor or my motor or John's motor with a P head making more power".

 

You can choose to require a form of proof that will not exist until you 3 put P90's on your engines (so basically it will never exist). I'll choose to side with all the experts, realizing that I'm not an expert myself and also realizing that you specifically state that you aren't an expert either.

 

EDIT--Found a better quote:

Absence of proof is not proof of absence.

William Cowper

[JMortensen]

EDIT: I wonder if there are such as thing as offset valve guides that could allow wider valve spacing ........

 

I'm sure the valve guide hole could be machined larger and offset to the side, then a regular centered valve guide with a larger OD and same ID could be installed to get the valves farther apart.

 

Then you'd just need one hell of a port job.

[gramercyjam]

I'm thinking a cylindrical steel blank larger in diameter than the current valve guide and centered where a stock guide goes, with a hole for the valve offset to the side of the steel blank. I'll probably never get around to this though unless I get my own machine shop.

[Dan Baldwin]

Yep' date=' I sure do. I AM arguing that the P heads are better. [/quote']

 

Clearly you have made up your mind and will not be troubled with the facts!

 

This is what I call "pseudo-certainty". Without any direct evidence, and based only on your own interpretation of what others say and your limited experience, you have arrived at a conclusion and won't be moved from it, nor even admit to yourself that you might be mistaken.

 

I dunno. Swap modded P heads (and pistons on John's) on all those motors and see what happens. I'm not about to try and duplicate all the work in those engines to prove a point to you.

 

Of course I don't expect you to do that. I'm not doing it either. But surely you don't suggest that an N42 head is not worthy of consideration in performance applications given these examples, do you?!

 

<snipped buncha links of *supposed* evidence for the P-head cause>

 

I CAN KEEP GOING. I CAN DO PAGES AND PAGES OF THIS.

 

No doubt! It still doesn't prove your thesis.

 

You've got imports, domestics, even ATV's in that list. Everyone seems to think that quench is an extremely beneficial thing, except you Dan. And you won't say that it is NOT beneficial, just that you need proof that it is .

 

I see at least PART of the problem with your reasoning. Magic word "quench". Instead of reasoning based on ACTUAL RESULTS, you've decided that 1) quench is all-important and 2) the P-heads = plenty o' "quench", while the N-heads =none

 

, and of course the above experts' clear explanations of why quench is important and beneficial don't qualify under your "show me Norm's motor or my motor or John's motor with a P head making more power".

 

I'm not saying quench is or isn't important. I will say this, if "quench" is required to run an L-series motor at 11:1 CR on pump gas, my N42-headed motor must have at least some of it!

 

In the end I'm not worried about "quench" or lack thereof, I'm worried about maximizing power over as broad a range as possible. If somehow I've employed "quench" to this end, FINE.

 

You can choose to require a form of proof that will not exist until you 3 put P90's on your engines (so basically it will never exist). I'll choose to side with all the experts, realizing that I'm not an expert myself and also realizing that you specifically state that you aren't an expert either.

 

You say you're "siding with the experts". But I don't think the experts would look at the evidence and then side with YOU. As far as I know, Sunbelt are THE experts on NA L6 engine performance. When I told them what I wanted (maximum power ~4k-7k, on pump gas) and asked if I'd be better off finding a P90 for 'em to mod, they said just send the N42. Whaddya know, it WORKED.

 

I say again, if "quench" is all important for a performance engine build, my engine, John's engine, Norm's engine, and the stock N47 head on stock flat-top bottom end engine Pete built for the ZCCNE club race car (see several posts above), must have it!

 

EDIT--Found a better quote:

Absence of proof is not proof of absence.

William Cowper

 

Again, I'm not *saying* there's PROOF of the nonsuperiority of P-heads!

I'm saying there's STILL no EVIDENCE of their superiority. Your willingness to throw the word "quench" around as if you KNOW what the experts are talking about doesn't affect my engine's, the ZCCNE club car's engine's, Norm's engine's, or John's engine's performance in the slightest!

 

I maintain that the best bet for the guy who just wants to put parts/pieces together to make a decent-performing L28 is to put an N42 or N47 on a flat-top F54 block. The ZCCNE club car's engine Pete put together pretty much proves this approach. 10:1 CR, pump gas, all stock, 164rwhp.

[johnc]

'Course, then there's the OS Giken DOHC head... (ducking)

[JMortensen]

This is what I call "pseudo-certainty". Without any direct evidence, and based only on your own interpretation of what others say and your limited experience, you have arrived at a conclusion and won't be moved from it, nor even admit to yourself that you might be mistaken.

 

Dan, that is what I call "pseudo-insulting." You and I have argued before and I have admitted when I was wrong. It wasn't that long ago either. I think we've argued points on this board or the IZCC list several times over the past 5 years or so. I don't know if all of them had an "outcome" or a "winner", but you should know by now that I WILL admit when I'm wrong, even if it takes beating me over the head with logic a couple hundred times to get me there. In this case though, I think it is you who doesn't have a leg to stand on.

 

I say again, if "quench" is all important for a performance engine build, my engine, John's engine, Norm's engine, and the stock N47 head on stock flat-top bottom end engine Pete built for the ZCCNE club race car (see several posts above), must have it!

 

John's engine has it. Norm's apparently has it (if what Bastaad says is true). Yours does not. If you would bother to read what the experts say about quench before deciding that you can't have an opinion about it you would have known that your engine couldn't possibly have it. If I recall your build correctly with pistons just below deck height and a 2mm gasket, your engine DOES NOT have quench.

 

You'd need a P90 with a gasket short enough to get the piston within about .040 to get the most quench in an L engine with flat tops. The N42 does have a very small bit around the edge of the chamber. You may say that this proves your point that it is not necessary, but I would say that I suspect you're missing out, and only have the hundred experts who may or may not have built an L engine to back me up.

 

The problem here as John said is that once you start modding the heads, then it all becomes a moot point, so I guess further arguing about it is pointless.

 

If you are not an astronaut believing only what you see makes you a good candidate for a Flat Earth Society membership.

[DAW]

Always a controversial subject, but jmortenson provides more than heresay in his references compared to the strong opinions in other posts.

 

Re the detonation issue, I don't look for validation in a modified engine that may be more forgiving re ping due to the non-stock cam. I think the more fair comparison between heads (with respect to factors such as sensitivity to variances in air/fuel mixtures, mpg, ignition advance, etc.) causing ping would be between two engines with comparable parameters and c.r. and the same stock cam in both.

 

This is where the weak links show up and you can infer from them that you are buying insurance for your engine's life and for uncompromised performance under a wider range of conditions in the engine which is least-susceptible to ping.

 

I think comparing a slightly shaved (not the huge 0.080" formula) P79 or P90 head on a euro-spec L28E (offset raised area on piston top) yielding about 10:1 c.r., vs an F54 flat-top with N47 (L28) head or N42 respectively yielding about 10:1 c.r., both engines with stock cam and cam timing, would provide a better platform for baseline comparison of combustion chamber effects. Set up with the same manifolds & injectors and transfer the engine management system from one to the other and swap the motors into the same chassis and compare dyno results, and drive real-world ping-generating conditions and record pings using a detonation sensor input. With each engine, vary fuel & timing parameters and chart against ping prevalance.

 

I'll choose the cyl head that pings least, with parameters being equivilant under demanding conditions, to use on a modified engine with higher compression and a performance cam because common sense tells me to select the quench configuration that yields the best baseline results.

 

From personal experience, I know my preference (I'll keep the hearsay to myself) but I'd put more stock into a controlled comparison. DAW

[johnc]

I think comparing a slightly shaved (not the huge 0.080" formula) P79 or P90 head on a euro-spec L28E (offset raised area on piston top) yielding about 10:1 c.r., vs an F54 flat-top with N47 (L28) head or N42 respectively yielding about 10:1 c.r., both engines with stock cam and cam timing, would provide a better platform for baseline comparison of combustion chamber effects. Set up with the same manifolds & injectors and transfer the engine management system from one to the other and swap the motors into the same chassis and compare dyno results, and drive real-world ping-generating conditions and record pings using a detonation sensor input. With each engine, vary fuel & timing parameters and chart against ping prevalance.

 

And I think that comparison will show that the differences will have more to do with external environment, driving style, and fuel quality variances then anything inherent in either cylinder head.

 

But, that's just another opinion thrown onto the large opinion pile. The pile's starting to stink a bit too.

[Dan Baldwin]

This is what I call "pseudo-certainty".

 

Dan, that is what I call "pseudo-insulting."

 

OOPS! Sorry, just gettin' frustrated! I will continue with the logic-beatings until you come 'round

 

On QUENCH, you pontificate thusly:

John's engine has it. Norm's apparently has it (if what Bastaad says is true). Yours does not.

 

So, we ARE to believe that "quench" is a property that you either HAVE or do NOT HAVE. On or off, 0 or 1. And we are ALSO to believe that YOU (a non-expert like myself) are able to determine the "quenchiness" of engines mostly unknown to you from a distance!

 

I must say, it seems to me that if my engine has no "quench", I really don't see why I NEED it! I mean, I'm making at least DECENT hp, I think?!

 

If you would bother to read what the experts say about quench before deciding that you can't have an opinion about it you would have known that your engine couldn't possibly have it. If I recall your build correctly with pistons just below deck height and a 2mm gasket, your engine DOES NOT have quench.

 

Neglecting my setup for a moment, if indeed my engine has NO quench, and yet has pulled 255rwhp at the dyno, on pump gas, wouldn't that lead you to question whether or not "quench", as you understand it, is really essential to have?! No, not you! My engine is CLEARLY deficient because it HAS NO QUENCH

 

Now for the particulars of my engine, before and after rebuild. I'll let you dub these setups "quenchy" or not as you see fit:

 

Previous build was with KA pistons, unshaved. Pistons had a raised ring ~.20" wide around the perimiter, which popped up .022" above block deck. The main surface of the piston was a flat valley .019" below the raised perimeter ring. 2mm head gasket. Cylinder head was (as you know) an N42, slight chamber reshaping (still very much "open" chambers) shaved ~.020", cc volume 40.6cc. Calculated CR was 10.74:1

That setup pulled 235rwhp on New England Dyno's Dynojet, on 93 octane pump gas, with 5 years, 40 track days, and ~30k street miles on the bottom end.

 

For the rebuild last year, the pistons were shaved flat (right at deck height IIRC) and relieved for valve clearance. Head gasket thickness now 1.17mm (2mm gasket minus one .33mm layer and one .5mm layer). Calculated CR = 11.11:1.

This setup pulled 255rwhp on New England Dyno's dynamometer last year, again on pump gas. RWHP was within a hp from ~32 deg to ~40 deg, so I set it to 34 (lowest advance that didn't cost me power).

I ran it again earlier this year and only made 238, but was having fuel pressure and throttle linkage issues. On that day, a couple of 350Z's made 240rwhp, to give a reference hp figure, and the club car w/ Pete's (presumably also "quenchless"?) motor made 164rwhp.

 

You'd need a P90 with a gasket short enough to get the piston within about .040 to get the most quench in an L engine with flat tops. The N42 does have a very small bit around the edge of the chamber. You may say that this proves your point that it is not necessary, but I would say that I suspect you're missing out, and only have the hundred experts who may or may not have built an L engine to back me up. .

 

But they aren't "your" experts. You don't "have" them to back you up (we haven't heard from them anyway). Experts are generally willing to look at evidence contrary to what they expect and either decide the evidence isn't valid or change their thinking a little bit.

 

You don't have any evidence, or experts to back you up, you have only a word, "quench", and a couple of criteria for whether it is present in an engine or not, and an unshakeable belief that any engine that doesn't meet this simplistic "quench" formula MUST be suffering a tremendous performance shortfall.

 

I mean, COME ON! If my engine and the ZCCNE club car's engine (I guess you've STOLEN John's and Norm's N42-headed engines from my side of the argument, no matter ) are so DAMNED "quench-deficient", how is it that the club car's engine runs fine and strong on pump gas at 10:1 CR with a stock cam and mine runs fine and strong on pump gas at 11:1 CR with a big cam? How is it I ran it for YEARS at ~10.5:1 with the stock cam?

 

If you are not an astronaut believing only what you see makes you a good candidate for a Flat Earth Society membership.

 

I believe what I don't see when evidence is presented. None has been. I don't believe I'm disagreeing with any "quench" experts, either, just you. You seem to dismiss valid data just because it doesn't fit your narrow world-view. You and the long rod/stroke ratio obsessed guy (oh, here he is now!) should get together, you're both MISSING THE POINT. Well, my point, anyway. I want to practically maximize performance <[edit] of the L6 engine>, irrespective of *supposed* "quench" (or lack thereof), *supposed* "optimal" rod/stroke ratio, F1 bore/stroke ratios, number of valves, number of cams, number of cylinders, etc. etc.

[Dan Baldwin]

Re the detonation issue, I don't look for validation in a modified engine that may be more forgiving re ping due to the non-stock cam.

 

FWIW, I ran my engine for years with the stock cam, at ~10.5:1 CR, at normal (~35deg max w/o vac advance) ignition advance levels. Maybe I was at the ragged edge, but the car ran great. Tens of track events, tens of thousands of road miles. The only times I detected pinging were when I was running too much advance (~43) and when I lost the mech. advance springs (boy did THAT cause some run-on!).

[Dan Baldwin]

That's all fer today, I know my posts read pretty aggressive, but know this:

I am only a searcher for TRUTH. NOTHING is meant personally.

[DAW]

I have noticed a difference in ping tendencies on two 2.8L, 10+:1 c.r. engines I have (both with N42s) with same ignition advance and same stock cams but different stroke length and rod/stroke ratios. One pings alot even with fairly rich mixtures (unless I back the timing off at the expense of throttle response and mpg) and the other never pings with a much leaner and more economical mixture. I'll let the reader guess which N42 application has the greater tendency to ping...I'm not going to contribute more hearsay myself. One factor differring between the two engines is that one is a mildy modified f.i., and the other triple sidedrafts. The one that doesn't ping has somewhat higher c.r. and higher cylinder pressures on compression test.

 

My gut feeling is that if I switched inductions between the two I would be leaning the carbs and richenning the f.i. but that's a hunch, not knowledge. I have to actually do it before I know.

 

For myself, I've learned something worthwhile by contrasting two engines while holding a major parameter constant (cyl head combustion chamber configuration). When these type debates come up I see people touting their results as spectacular (I believe them) and I'm very impressed. What I don't see is the same people doing the legwork to compare the variable (such as N42 vs P90) for themselves before they speak out and therefore not being in a position to comment with credibility. You have to wonder when you read accounts of successful builds using an N42 or P90 head whether the same c.r. engine and setup they built would be less powerful, more powerful, essentially equivalent, or have a hole in a piston with a P90 or N42 respectively...but no one seems to compare for themselves, they just jump on their bandwagon and campaign their cause.

 

To compare, you've got to do a comparison and not present a diatribe on your personal engine setup as it is. Change the variable at hand and report back. (boy, am I goin' to hear it on this one) DAW

[Guest bastaad525]

and round and round it goes...

 

 

do you guys ever notice, that every so often some newbie will show up, ask this question, start a 5 page long feud, but that said newbie-thread-starter never even checks back in to get his answer, whilst we just go round-and-round in the eternal debate?

 

Dan - I had mentioned that I had read a TON of evidence, much of it not even Z related, but most of it written by 'experts' or at least, convincingly enough to make me think so, but all of it in support of closed, semi - circular or heart shaped champers working better than open chambers. Jmortensen listed a LOT of links, and some of those I have been over myself and were the kinds of things I was talking about. There really are a lot of people out there, from guys like you and me to professional engine builders, who think this is the case. And personally I don't necessarily believe everything I hear from the guys at Sunbelt or Rebello anymore either. YES they do know what works, but, they may also be 'stuck in their ways', as many 'old timers' can be some times... they started with N42's because they worked, and worked well, even w/o modification. But when the word that the P90 was possibly better start proliferating, well.. you know how some people can be... they just can't be told any differently. At least you're having an open mind but just saying "show me proof"... but well... with the guys at Sunbelt and Rebello, they just may be stuck in their ways. A sort of indirect case in point... exhaust shops. If I had a dollar for every closed minded exhaust shop guy who will sit there and argue with me allll day why I don't need an exhaust larger than 2.5" on my turbocharged Z, how I will LOSE power if I do, am wasting money, yada yada yada... well I'd have enough to buy me a 3" exhaust already! At least in this case there is proof to the contrary... too many guys having upgraded to 3" mandrel and seen irrefutable evidence that on a turbocharged car it makes more power, that there is no such thing as too big on these cars... but even with that proof, some muffler shop guys will still go out of their way to argue, saying it must have been because of something else. I had a debate just a month ago with one of these guys... he was a young guy too, no older than 30. I showed him Jeff's website (the moster 400+hp 280zxt) with the before and after dyno charts when jeff installed the 3" mandrel system on his friends ZXT... and the guy still argued it. Set in his ways.

 

So... no one has actually tried an n42 and a shaved p90 on the same motor and said which would make more power... but surely someone, SOMEwhere has done some comparison testing on some kinda motor/car and found that the heart shaped chambers did provide some benefit over open chambers... I mean the 'rumor' MUST have started somewhere. So what makes our Z's so different to say that this same thing doesn't apply to our Z's? I find that most performance 'tips and tricks' are pretty universal... as are many things that apply to motors in general. I'm sorry but having read so much in support of the heart shaped chambers I dont' NEED dyno verified proof to think that they work better. How much better? I have no idea. Maybe not much at all. Enough to justify doing all that extra work on a P90 to get a similiar compression ratio as the N42... well if I've go the money to spend and am gonna be trying to wring every last ounce of performance out of an N/A motor, hell yes.

 

 

And dont' worry, it takes a lot of forum trash talk to get me offended I'm always open for good healthy debates, and try to remain as open minded as possible... the best way to learn as much as I can.

 

I've suggested stuff like this before and no one has taken me seriously... I dont' really expect anyone to, but I know Norm has said that, if someone 'gave' him a P90, he'd be more than happy to test this theory and put the debate to rest once and for all. Anyone got a spare P90 they can lend him? Surely someone has one just laying around... Norm'd probably do all the modification work himself so cost should be small or nothing... maybe just 'lend' him the head? something? hundreds of guys on this board all very interested in the answer to this very question... instead of arguing about it maybe we should somehow collaborate to finally get the question answered??

[Dan Baldwin]

When these type debates come up I see people touting their results as spectacular (I believe them) and I'm very impressed. What I don't see is the same people doing the legwork to compare the variable (such as N42 vs P90) for themselves before they speak out and therefore not being in a position to comment with credibility.

 

You haven't been reading what I've been saying, which is that there isn't sufficient EVIDENCE to say that one head type is better for performance than the other.

 

THAT is the difference between my point and the opposing point. I don't know and I KNOW I don't know. The other point of view doesn't know, but they THINK they do. All I'm doing is pointing out that they DON'T.

 

I think I speak at least SOME credibility when I say "I don't know" despite having what would appear to SOME (not me) as concrete evidence of N-head superiority. Much more credibility than those who blindly tout the superiority of the P-head with no evidence whatsoever!

 

I'm not about to sink a lot of money into a P90 head as I *am* pretty sure that if there's ANY to be gained, it ain't much. Even if I did, I *hardly* think I'm qualified nor do I have the resources to do a true scientific test comparing ONLY different cylinder head chambers.

 

I am trying to be the voice of REASON.

 

To compare, you've got to do a comparison

 

and not present a diatribe on your personal engine setup as it is. Change the variable at hand and report back. (boy, am I goin' to hear it on this one) DAW

 

Obviously, I'm not going to be doing this. But, like I said, I'm not the one making unsupported claims. My engine is the one I know the most about, and it appears to be something of a benchmark in the sea of street na L-engines. I'm not going to sit back and let people be told the shave/shim/revalve a P-head approach is the ultimate answer when I'm swimming in evidence that an UNMODIFIED N-head is a damn good option for a decently high CR n/a L-engine.

[DAW]

I don't think a comparison between an 0.080" shave/shim/revalved P90 head is a valid comparison to an uncut or mildly shaved N42 head because of the huge amount of mass removed which likely affects heat dispersion. A P90 and N42 would need to be compared on an engine with equivalent displacement, bore/stroke, rod length, etc. and I rarely have seen such a comparison. One reason for this is that the P90 has a much larger combustion chamber volume which means you can't just slap the heads onto the same shortblock and have a valid comparison. The P90 would need the suitable pistons to work as designed. This means that an F54 flat-top shortblock (8.8:1 c.r. with P90 head) has to have raised-top pistons such as the Euro version which only increases c.r. to 9.3:1 or so, or a more prominately raised-top piston to yield 10+:1 c.r. to compare to the F54/N42 engine.

 

Alternatively, a dished-top piston, 2mm gasketed, N42 turbo engine could be compared to a flat-top piston, 2mm gasketed, P90 turbo engine. With the same turbo (limited boost due to c.r.)/injectors/ ECU used it would provide a fairly level playing field to compare.

 

This is really the crux of this argument, you have to limit all variables except the heads and that's rarely done. What is crucial for many people is that they do the comparison themselves or they'll never trust the opposing point of view. That's the way people "KNOW" what's valid. DAW

[Dan Baldwin]

Dan - I had mentioned that I had read a TON of evidence, much of it not even Z related, but most of it written by 'experts' or at least, convincingly enough to make me think so, but all of it in support of closed, semi - circular or heart shaped champers working better than open chambers.

I'm sure this is GENERALLY true. But we're talking SPECIFICALLY about the Nissan L6 N-heads and P-heads. *Perhaps* the Pheads SHOULD be "better". But the EVIDENCE hasn't beared this out.

 

Jmortensen listed a LOT of links, and some of those I have been over myself and were the kinds of things I was talking about..

 

GENERALITIES. We're talking about SPECIFICS here. Generally speaking, a Ferrari will handily outrun a Dodge econobox of the same year. But SPECIFICALLY, a GLH-S WILL hang with a same-year 328. All that glitters is not gold. Just because the P-heads *LOOK* like they should be higher-performance does not make it so. Nor does the low-performance *appearance* of the N42/N47 make THEM unsuitable for higher-compression high-performance applications.

 

There really are a lot of people out there, from guys like you and me to professional engine builders, who think this is the case. And personally I don't necessarily believe everything I hear from the guys at Sunbelt.

 

So, you'll take the word of "guys like you and me" and professional engine builders speaking either about OTHER engines or GENERALLY, over the ACTUAL WORK DONE SPECIFICALLY ON L6 ENGINES done by a company that builds WORLD CHALLENGE RACE MOTORS for MAZDA?

 

I'm not saying they know everything, but they apparently know more about how to extract performance from NA L6 engines than anyone on this forum.

 

YES they do know what works, but, they may also be 'stuck in their ways', as many 'old timers' can be some times...

Not my impression of Sunbelt at all. The best engine developers should never get "stuck in their ways", because their WAY is to practically maximize performance and not be distracted by spurious details like whether or not the head *looks* like it should or should not be "detonation-prone". If appearances are deceptive, they'll LEARN from the experience and not stubbornly cling to preconceived notions. In the end they will go with what WORKS.

 

A sort of indirect case in point... exhaust shops. If I had a dollar for every closed minded exhaust shop guy who will sit there and argue with me allll day why I don't need an exhaust larger than 2.5" on my turbocharged Z

 

C'mon, exhaust shop guys are not engine developers. I've never asked for exhaust design advice from an exhaust shop! I figure out what I want and say "do it THIS way".

 

I showed him Jeff's website (the moster 400+hp 280zxt) with the before and after dyno charts when jeff installed the 3" mandrel system on his friends ZXT... and the guy still argued it. Set in his ways.

 

I feel this is what I'M up against! I give hard cold evidence that you CAN run high compression ratios successfully with N-heads, and it is totally ignored! All I hear is: "It has no quench! It's detonation-prone!"

 

So... no one has actually tried an n42 and a shaved p90 on the same motor and said which would make more power...

 

Such a test would be hugely impractical, if it were conducted in a truly scientific manner. Numerous build-ups and teardowns, hundreds of precise measurements, it would go on and on. Basically you'd have to independently optimize EACH setup, and you'd have to compare at least three different configurations dozens of times. A simple dyno test with one head, then with the other will NOT suffice.

 

but surely someone, SOMEwhere has done some comparison testing on some kinda motor/car and found that the heart shaped chambers did provide some benefit over open chambers...

 

You're WAY oversimplifying things. Some kinda car with some kinda heart shaped chambers that outperformed some kinda open chambers would NOT prove now and forevermore that "heart-shaped chambers are always better than open chambers", much less that more specifically "nissan L6 P-heads are better than nissan L6 N-heads".

 

I'm sorry but having read so much in support of the heart shaped chambers I dont' NEED dyno verified proof to think that they work better.

 

Absolute PROOF is something that we're not realistically going to get. I've just been saying, forget proof, I haven't even seen ANY EVIDENCE AT ALL! Again, I'm not talking about heart-shaped chambers vs. open chambers in GENERAL. I'm specifically talking about the N42/N47 and P79/P90 heads. If heart-shaped chambers are IN GENERAL better than open chambers, that still does NOT say that Nissan L6 P-heads are better than Nissan L6 N-heads specifically.

 

How much better? I have no idea. Maybe not much at all.

 

*Maybe* not ANY at all. *Maybe* WORSE!

 

Enough to justify doing all that extra work on a P90 to get a similiar compression ratio as the N42... well if I've go the money to spend and am gonna be trying to wring every last ounce of performance out of an N/A motor, hell yes.

 

Similar compression? I thought the supposed P-head benefit was the ability to run higher CRs?

If you're going for maximum performance, you'll be modding the head anyway. So from that standpoint you're certainly justified to start with the head you *believe* will offer greater performance. From what I've seen, if I had to do it again, I'd go with whatever was readily available and not be too worried about N vs. P.

However, for someone who wants to do a quick simple performance NA L6 build, the N42/N47 on a flattop bottom end option is still clearly the way to go, IMO.

 

I know Norm has said that, if someone 'gave' him a P90, he'd be more than happy to test this theory and put the debate to rest once and for all.

 

That would certainly get us some GREAT experimental data points, but wouldn't put it to rest, wouldn't constitute "proof" one way or the other. For one thing, if he DIDN'T go faster, the P-head contingent would come back and say his N-head had been modified to become, essentially, a closed-chambered P-head!

 

In the end, based on what I know of other engines, regarding what CRs can be run vs. bore size, what kind of torque/liter they get, etc., it seems to me that the N-headed flat-piston L6 does pretty damn well. I don't believe it to be deficient regarding what compression ratios can be run with it. And I don't even know if I'm at the limit at 11:1. I had wanted to go for 11.25:1, but it wasn't in the cards due to piston/valve clearance issues. Could you go even higher with a P90 head? Perhaps... I'm just saying it is by NO means a foregone conclusion.

[z-ya]

For the people that are convinced that the P series head is superior to the N series (I'm certainly not), I'd say go with what you believe in. spend the extra $ on machine services and "maybe" you will have a better performing head.

 

This of course means that there will be more N series heads around for the rest of us

 

Pete

[JMortensen]

This of course means that there will be more N series heads around for the rest of us

 

Not really, because for those of us running stock valves we'll still need to get the N heads for the longer valves. We'll just take the valves out and throw the head away...