Dan Baldwin

First off, CONGRATS on gaining 40hp!!! Secondy, ditto on the non-validity of comparing dyno results from different dynos at different shops in different states under different environmental conditions. You're still running 40mm carbs, no? 44s or 45s, with 38 or 39mm main venturis should give you a broader torque peak, more peak power, and more power under the curve. What's your compression ratio? Torque seems low, I'd expect 200+ lb-ft peak, over a fairly broad range. With that cam you should be able to run ~10.8:1 on 93 octane pump (I am at 11:1, with ~305/.550" cam).

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

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. 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.

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.

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, 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: 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?! 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. 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? 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.

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

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 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. 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: 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. 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?! "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

Bastaad, Much appreciated you didn't take my post personally! I can appreciate your trepidation about the N42 if you had the problems you mention. I never had such probs. Despite the fact that I was running LEAN up top with the SUs. Enough so that the car would begin to overheat after a few laps at speed on warmer days. With the 3x2s (only semi-tuned, still a little lean up top at 13.2 - 13.8:1), no overheating, at ~240-250rwhp, with a stock replacement 3-row 260z radiator, and no oil cooler Heart-shaped vs. open chambers: Remember that VW commercial years ago about the boxy Golf actually being more aerodynamic than a swoopy Porsche 928? I think it's the same thing here. There's just way too much subtle stuff going on to categorically say that chambers of THIS general shape are always better than chambers of THAT general shape. In the end we DID make the same point, but I'm never above arguing Ditto what John said. If I were turboing, I'd definitely go P90. For NA, N42. Shaved P90 should get you to pretty much the same place, but with more effort. My engine builder had a helluva time getting my engine to 11:1 with the N42, I wonder if it would've even been possible with a P90.

And ALL of those arguments are solely supported by SPECULATION rather than HARD DYNO NUMBERS OR TRACK RESULTS. 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. If these heads are "designed" for a turbo, that in no wise indicates superior performance for an NA application, the argument could just as easily be made that SINCE they are (supposedly) DESIGNED for a turbo that they are deficient in NA apps. Please note that I am NOT making this argument, only saying it *could* be made! Point#2: zero evidence. What is important is not which LOOKS more like a "high-performance" combustion chamber, it is which ACTUALLY PERFORMS better. "Heart-shaped combustion chambers" does NOT necessarily imply "better performance. FWIW, I didn't have any noticeable detonation problems running ~10.5:1 CR with a STOCK N42 head and STOCK cam at ~35deg advance (though I DID experience detonation with that setup when I ignorantly tried to run 18deg initial advance with a stock distributor, which gave me ~43deg total advance!). Currently I'm at 11:1 CR with mostly stock N42 chambers (shaved maybe .020", mild reshaping, chambers still very much "open"), and running PUMP GAS. Dyno'd 255rwhp last year (only 238 this year, gotta find out why...). NOT TOO SHABBY. point #3: no evidence I'm not saying the same setup with a P90 would make LESS, or MORE power. Just saying that if there is SCIENTIFIC eveidence of P-head superiority out there, I have not seen it. I *think* Norm's head is shaved ~.040", I *believe* he has said this makes it more of a "closed-chamber". But it certainly didn't make it a P-head! P79/90 have to be shaved ~.080" for decent compression on a NA motor. But you can't ascribe Norm's performance to his N42 being "modded like you would mod a P90"! Is all or most of this inherent P90/79 performance advantage in the modification (serious shavage) required to make it a viable NA head?! Agreed. Just be sure you can separate HARD EVIDENCE from unsupported SPECULATION! Dan "I'm NOT saying the N-heads are 'better'!" Baldwin

Oh yeah, I was there.... OK, 2x 1st hand info on the stock N47 being A-OK Sounded SWEEEEEET, too as I recall

swither2, IMO, best easiest bet is a N/A F54 bottom end from a 80+(?) 280ZX non-turbo, which has flat-top pistons, and either use your '72 E88, or an N42 or N47 head from a 280Z (same cc size as the '72 E88, but bigger valves), or shave the F54's P79 head ~.080", shim the cam towers, and use the earlier slightly longer 280Z valves. 2.8 liters and ~10:1 CR, should give 15-20% more torque and power than the L24.

Just a couple more points (I appear to be a post or two behind...): "follow-the-sheep"? It is MORE stupid to discount out-of-hand a proven reliable method just because so many have already done it as it is to follow same method without understanding WHY. Grandpa? Again we gain insight into DAW's totally unscientific reasoning. It is an "old" recipe, therefore it is no good, huh? Yeah, no kidding! (got a chuckle out of that one) FWIW, max piston accelerations are equivalent for the following: 1.6:1 r/s engine @ 7000rpm 1.69:1 engine @7044rpm 1.79:1 engine @7089rpm There IS SOME theoretical redline increase to be had with longer rods, it just ain't MUCH. "more unique"? No such thing. Something either IS unique (only one) or it is NOT unique. To quote Ecclesiastes: "there is nothing new under the sun". Another good one: "all is vanity". I wouldn't get TOO caught up in trying to be different for no other reason than JUST to be different. Promoting "your" idea (and it AIN'T your idea, old as the hills...) of maximizing rod/stroke ratio at the complete disregard of practicality to OTHERS who seek advice doesn't seem warranted to me, though. I NEVER EVER SAID THIS!!!! My point all along has been that there is little to no *evidence* that rod/stroke ratio (over a reasonable range) makes a significant difference in engine performance. Longer rods make for less side-load on the piston, that's good. Longer rods reduce peak piston acceleration, also good. I just don't think it's worth fussing with an LD28 block to get these small benefits, and any PERFORMANCE benefits are more a matter of quality than quantity. Supposedly shorter r/s is better for low-midrange and longer r/s better up top, but not by any significant margin. All that said, I wish you the best with your LD28 build, and I hope it fits OK. I just don't think you're doing anyone any favors by INSISTING that a longer r/s motor is going to be demonstrably better-performing than a shorter r/s motor, without having ANY evidence whatsoever. Someone TOLD you big r/s is better, you reasoned in your head "yessss, it IS better, MUCH better, FAR better!" But you haven't presented a CASE.

jmortensen and (goldfish) The average piston speed HAS to be the same regardless of rod length, it's only a function of stroke and rpm (long rod or short rod, the piston goes up and down the same amount, the stroke dimension). A shorter rod increases angularity, which causes the piston motion to be sort of exaggerated at TDC, as the rod "standing up" increases the vertical motion of the piston. Near BDC, the rod "standing up" DEcreases the downard speed/motion of the piston. At TDC and BDC, the reduction of rod angularity tries to move the piston UPward. And for the incomparable DAW: I didn't note Isky referring to exotic and extreme measures anywhere, basically he's saying there's no need to bust your balls to get a "good" rod/stroke ratio. In THIS case, two blocks are NOT sitting in front of the guy we're trying to help, ToplessZ: "I wish I could find an ld28 block around here. " he says. Yet you continue to present the LD28 block idea as the ONLY way to go! From another post BobH (back in town?!) says "The LD28 block had a 84.5mm bore. Those that have actually taken the LD block and tried to get a "larger" bore than the L28 block were only successful in getting it out to about 88-89mm" So, to answer DAW's question: If the 1.8 rod/stroke ratio block started at 84.5mm bore, and the 1.6 rod/stroke ratio block started at 86, and I wanted a 89mm bore, I'd go with the latter. DAW, the quote you give doesn't seem to be applicable to the current discussion. My point was and is that there's not much to be gained by going out of your way (LD28s apparantly not exactly readily available, possible/likely hood mod required, other potential fitment issues apparently including header clearance?) to put a taller LD28 block in a Z in order to get a supposedly more favorable rod/stroke ratio. The "hammer" of logic, science, and REASONING is a pretty useful tool, you might try it sometime!

Good link, John. Some people will go to ridiculous lengths just to get the "ideal" bore/stroke or rod/stroke ratio, even if it leads them in the direction of less displacement (and torque/power)! Funny...

If you DO have to butcher the hood to use the LD28 block, that would eliminate it from consideration for a lot of people (myself included). Keeryst, DAW, you don't have to be an ass (or maybe you do). You're missing my point entirely. And at least ONE small-block build-up in Hot Rod way back when found more power with 5.7" rods after doing a comparison study. Not that THAT means SHORTER rods are better, it doesn't. I just haven't seen any EVIDENCE that going out of your way to build a long rod L6 has any measurable benefits. Feel free to demonstrate this. And they are, of course, the pinnacle of internal combustion engine design... Of course they don't "ignore" it. They also have a lot of other stuff on their minds other than maximum performance. If there is a trend toward larger rod/stroke ratios in the automotive industry, that doesn't *necessarily* imply that that's "better" for US. Unfortunately it's also ugly as hell. So TURBOCHARGING is a SOLUTION to potential interference problems using an LD28 block?! I think you have overstated the benefits of long rods to yourself to the point that having long rods is the ultimate (only?) goal of your project! If having a turbo facilitates that end, then turbo it is! I hardly think the decision to turbo or not should hinge on whether or not it allows use of the taller LD28 block. In the end, I totally understand that the typical stroker engine has a rod/stroke ratio (1.6) that's low relative to other engines. I can certainly appreciate that there *might* be benefits to having longer rods. I just don't think that they're likely to be worth going too far out of one's way (custom rods/pistons/taller block) for for *most* L6 engine builds. Somewhat interesting reading here: http://www.stahlheaders.com/Lit_Rod%20Length.htm

Can the LD28 block be bored to 89mm? Does it fit (seems like I read/heard the cam cover comes pretty durn close to the hood)? Whatever block is used, I'd still go with the LD28 crank and "worse" rod/stroke ratio *for an N/A build*. Turbo, I'd probably just use a stockish jy L28 bottom end and spend all $$$ on ancillaries. Anybody really *know* how much rod/stroke affects detonation, allowable CR, allowable boost levels on a turbo L-series? For N/A, the benefits of "better" rod/stroke seem to be way overstated to me, turbo might be a different story...

My thoughts: increasing rod/stroke via 140mm rods will increase rev potential of a 7000rpm motor to... 7042 (for the same max piston acceleration). Don't bust the bank trying to get a "better" rod/stroke ratio. More stroke is going to improve off-boost AND on-boost torque. Destroker is not a good idea unless you're in a displacement-limited race class. Sure you get slightly more rev potential, but you lose more torque than you gain revs, so power potential drops, and you've lost torque everywhere in the rev range. I ran my 3.1 for YEARS with the stock 240 damper, swapped in the Nismo single-groove (that's all my parts guy had at the moment, I actually wanted the 2-groove) last year due to the rubber in the stock one visibly dryrotting. I shift around 7k, rev limited to 7200. I have had issues with flywheel bolts loosening on me, once after 5 years of usage with a stock lightened flywheel, and a year later with the aluminum flywheel and no washers (dumb). Since had the Al flywheel holes bushed. Fingers crossed, but think I'm ok. No such probs with the damper bolt loosening. IMO, even with a turbo, maximize displacement, subject to how much you're willing to remove (turbo may want thicker cylinder walls) and how much you wanna leave for future rebuilds as John suggests.

You're talking KA24 pistons, right? Pistons pop up ~.025" (measured mine at .022"). The KA pistons have a raised (.019") ring around the perimeter. Machining this ring off will have zero structural integrity ramifications, would give a popup of ~.003"-.006". Go ahead and machine .025" off to ensure no pop-up. This won't affect CR much (LEngine builder doesn't calculate this properly and will overestimate the CR loss from machining dished pistons). Or, you could leave the pistons alone and use the 2mm HKS head gasket. You will have to shave the P90 ~.080" to get a decent CR (and shim cam towers, and use older N42/N47 valves). Or you could just use a stock N42 head for 10+:1 with the 2mm gasket. 4bbl conversion not the best way, IMO. Depending on what you want, street performance vs. all-out track hp, I'd recommend stock 44mm SUs, 2" Jag SUs, or 44-45mm 3x2 carburetion.

Mine ain't exactly like John's, I don't think. ~.550 lift, ~310 duration. Idles ~1000-1200, I do have to help it with the gas pedal sometimes, VERY lumpity:) Frequently accused of being a V8. Not too bad on the street as long as you don't care who beats you across the intersection! Nobody home below 3k. I think the 272/.477"(?) cam he's got sounds good for the street. I wouldn't go beyond ~290/.490" for a non-competition car. I've got 38 (39?)mm chokes in my 45mm carbs. Figger maybe 36mm chokes would be appropriate for this setup. Should be fun!

PUSHER, An E31 head on a flat top L28 would make 10.2:1, that's probably what you were thinking of. Probably stock or Felpro gasket would be fine, and a lot cheaper than an HKS metal one. For hp estimation, I've heard/read that a straight ratio of compression ratios will give an estimation, albeit an optimistic one. I figure, all else being equal, and within the CR range that works for available fuel, you should be able to get at least half that gain. 10/8.5 = 1.18, figger that means at least a 9% gain in torque EVERYWHERE in the rev range. Woohoo!

Yup yup yup, 280Z N42 head on 280ZX NA F54 block => 9.8:1 CR, along with the 280ZX 5-spd and diff, SWEET setup! '75 has dished pistons. You won't have any piston/valve intereference problems unless you go with a pretty high-lift cam.

Put 'em back in the same order. Mine were actually stamped with one punch mark on #1, 2 on #2, etc.

I've gotta chime in that there is still no credible evidence that the P-heads are superior to the N-heads, stock or modified. There's just no such evidence (to my knowledge) out there. The ONLY argument I hear lauding the P chambers is that the chambers LOOK better. Lots of stock and modded N-heads that don't suffer from the "detonation-prone" problems they're supposed to have. I for one wouldn't go to the effort of shaving and shimming a P-head when an N-head doesn't require nearly the butchery to get the desired compression ratio for an NA application. For a turbo, I'd use the P90, no question, again because of compression ratio.

Here's why the destroked L28 idea sucks: You want POWER. Power is TORQUE times RPM. So you want TORQUE and RPM equally badly. Destroking an L28 will LOSE you torque, but GAIN you rpm. The PROBLEM with that is that it loses you MORE torque than it gains you rpm. The reason for this is that torque varies linearly with stroke, while rpm potential varies approximately with the SQUARE ROOT of stroke. Decrease the stroke by 7% and you lose 7% of your torque, EVERYWHERE, but only gain a theoretical 3.5% in redline rpm (only helps you at redline/rev limit). Actually, accounting for the "better" rod/stroke of the L24 crank/rod combination, you theoretically get 4.6% more redline. That doesn't make up for the 7% torque you lost, and again the torque is missing EVERYWHERE, while the rpm gained is only at the very top. Put flat-top pistons in the L28 with the N47 head and you'll be doing fine. Gearing will depend on which 5-speed you have. Go here: http://www.geocities.com/z_design_studio/