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200+ WHP NA build


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I've got a mostly stock 260Z that is a typical "sunny day" car - but lately its been upstaged by my new daily driver - an RSX type S. Fortunately I just dropped my daughter off at college for her last year, so come spring I'll finally have a few bucks to sink into the Z. My goals are more subjective than logical:

  • Feel faster than my RSX.
  • Run triples. I know I'll probably get tired of tuning carbs and swap to ITBs or something, but I've lusted after Webers (or Mikunis, Dels, etc) for a long time.
  • tHave a usable redline north of 7K RPM. I know its more efficient to make power at lower RPMs but I want to hear an exhaust note that makes me feel like I'm Paul Newman at Limerock.
  • A smooth idle and linear throttle response.
  • Run on 93 octane.

The RSX weighs about the same as an S30 and according to the internet puts down around 165-170 whp, so I'm thinking I want about 200-210 whp, or approx. 250 crank hp. I've been searching the internet and doing back-of-the-envelope estimates to figure out how to do that. What I'm leaning towards is (roughly) 88.5mm bore L28, stock L28 crank and rods, high-silicon forged flattops, 10:1 CR, quench head, 45mm triples, mild cam (aprox .490 lift, 270 duration). Mild cleanup port on the head - unshroud the valves - but don't go too big on the port to keep velocity up.


Basically a mild stroker build without the long crank (to give me my 7500 RPM redline without radical porting).


Things I couldn't find good answers for:

  • Best way to get a 10ish CR with a quench head? Can an MN47 be opened up to 46cc combustion chambers? I'm nervous about the shim-n-shave mode for the P79; all those shims stacked under the cam-towers seems a little scary at 7500 RPM... Maybe go with the Kameari idler gears and adjustable cam gear?
  • Is there any benefit to using L24 rods with the L28 crank? I've plotted the piston velocity curves with both rod-lengths and the extra 3mm just doesn't seem to amount to much? Keeping the shorter rods might actually help by creating more intake "vacuum" early in the intake stroke to squeeze a little more flow out of the carbs (45mm seems a little on the small side for a 250 hp motor). Any real world experience here?
  • Undoubtedly lots of things i haven't thought of yet... I'm trying to settle on a block and head before I get into more details.

Opinions, ideas, experience welcome.


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Yes it can be done. A reasonably stout 3.1L stroker build with triples can get you to 200rwhp, maintain street-ability, and be faster than your RSX. If you insist on 7500rpm or more you are going to add a lot of (needless) cost to meet your other goals.


I built a customer engine with typical L24 rods, LD28 crank, .120 over, KA24 Pistons, P90 head, reasonable performance cam... Triple weber DCOE40's, in a very good state of tune, and we made over 200rwhp (211 tickles my memory) on the dyno. Not to say every setup with these specs would make this power, but if you port match, tune well, etc. it's completely achievable without breaking the bank. The engine felt stronger than my 231rwhp/280ft-lbs L28ET did in a 240z, and made all the right sounds and drove fantastically.


If you insist on 7500rpm, smaller displacement, etc. to make the same power, I can see you spending a lot more dollars (double?) to achieve the same power and less torque.


As for the RSX... it was faster than the RSX-S with a Greddy 7psi turbo kit in a good state of repair and tune... so yeah, it will be faster than your NA RSX-S.

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We just dynoed the car, and it went pig rich at 6500 leaving us with a dissapointing 256 RWHP. The engine just starts to pull hard at 6K...


All from 2.8L N/A...


Only 200? Piece of cake. 7500? Forged internals, you can make 200 to the rear wheels with cast pistons at 6500 easily enough.


Hell, my bone stock L28 running the stock EFI makes 147 to the rear wheels...


If you want high rpms for some auditory masturbation, more power to ya, but it will run you cubic dollars and it's wasted if you are only planning on making 200HP.

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If you want the rpm then stick with a 2.4L L6. It does a little bit better then the 2.8L at high rpm. You can make 200hp easily with an NA L24 given freedom in head, cam, and piston choice. And the RSX weighs at least 350 lbs more then your 260Z unless its full of junk.

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Tony, I'm sure you can get 200 whp from a stock displacement L28, but I'm thinking it takes an 11:1 CR and a big cam. I'm not quite sure how to read your example; if you're saying someone pulled 256 HP at 6500 RPM from a stock displacement L28 I'm impressed - that works out to a LOT of torque and a ridiculous CR (13:1?). If they pulled the 256 at some higher RPM (after the AFR went rich) then its still impressive but a little more believable. The "just starts to pull hard at 6K" is what I'd like to avoid. I'd like to pull hard from roughly 4K to 7K, and I'm willing to trade some absolute top-end power for mid-range.


I know I could get the whp easily with a 3.1 build, but they all seem to max out around 6500 RPM or less (a lot of them seem to run 40mm triples which seems a little small for 3.1L, maybe they just need bigger carbs?) As I said, I have this totally irrational perception that its not a sports car if you can't wind it to 7000. I know its not going to be the fastest car on the road; me being happy with the way it drives is more important than a bit more acceleration I'll only notice if I drive around with a stop-watch.


I thought the L28 crank, rods and cam were reliable to 7-7.5K - the expensive part being forged pistons? That seems like at most an extra $600 - a little less if comparing to cast pistons. Doesn't seem bad for peace of mind and not a lot in the grand scheme of an engine build. Or am I missing some other money-black-hole?





John, if there are L24s out there making an easy 200 whp I'm reading the wrong books and web pages... that seems like race-car territory (100+ bhp/l). Can you outline the build? You're right about the weight of an RSX - its closer to the weight of a 280Z, the 260 is lighter and that helps a bit; I could lower my hp goal by about 15% which would be a lot easier to reach - but once the engine is done I'll probably be thinking R200 and 5 speed, which will erase most of the weight advantage. I think I'll stick with my 200 whp target. I did briefly consider a frankenmotor: L24 crank and rods in an L28 block with 88.5mm bores (I think it works out 2750 cc) - good for style points - but given my goals I'd rather have extra displacement.




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100hp per L is a mild race engine build. 2.4L L6 engines built to ITS rules (stock cam, crank, pistons, SUs, no porting, etc.) make 208hp at the crank. FP 2.4L builds make more then your magic whp number with 12 to 1 CR, .500 lift cam, SUs, header, etc. and spin past 7,500 rpm.

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Yep, the roads were full of 320HP, 8Krpm L24's in Japan 20 years ago.


The reason L28 Strokers 'peter out' by 6500 is the cam selection. I can think of several offhand which don't.

In fact, Burton Brown's 3.0L running at Bonneville broke the record while he was granny-shifting at 6000-6500 rpms on that monster. How much horsepower does it take to push a bone stock S30 to 173mph with that big, open maw?


If you want 'streetable' and defy logic by stating you MUST have carbs... :rolleyes:

Monzster's L24 sings to 8,000+ (videos exist here) and is completely streetable. It also used EFI. Our old build ran 45 DCOE Webers, and would NOT idle worth a damn below 1700 rpms.


Put EFI on it with ITB's and on a 39F morning at 2500 feet altitude it starts and idles just fine, settling in to a 950 curb idle when warm.


And yes, it pulls beyond 8K. Power comes on STRONG at 6K. You wanted 200HP? It's making that well before 6K. The example was to open your eyes that with a slight cam change the entire power band will move down a quite a bit. The CR doesn't give you as much as you would think. Our 2L L20A made 205HP and we were lucky if it had 11:1 CR.


Like JC stated, you are in the 'tuned stock N/A range' for an ITS car. No exotic parts needed.


If you want 7K+ solely for some aural fixation... again :rolleyes:


200 is doeable and cast is fine if you don't go over 7K.


Don't forget to put in that 4.44 rear gearset so you will have the opportunity to use the extended RPM range.


If you "lower your goals 15%" you are LITERALLY in the "bolt-on, don't touch the longblock" area of power possibilities. As I said, my bone stock L28 car spun the dyno to 147 to the rear wheels. And given the weight and 1/4 times it turns consistently all the calculators say I have 202+ HP.... And all I did was degrease it after pulling it out of a Junker $100 1980 280ZX 2+2 (not your expected junkyard donor for latent, hidden performance goodies...)


Again, the key to street driveability is to NOT go with carbs. They don't function well at lower speeds people like to use for street driving. It's a function of the carbs, and nothing more. EFI solves that problem. Tractability is amazing. And it sounds just the same (listen to Monzster's white car running the Auto-X course and tell me it doesn't meet your desires... then again it's more like 300+ HP on an L24 and you want 2/3rd to just over 1/2 that!)


Rpms need not enter the equation.

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My point on the EFI over Carbs was if you DO have a 'monster cam' you will find that what is 'undriveable' on Carburettors is ENTIRELY different on EFI.


Like I mentioned, the LSR car would not idle below 1700rpms, simply because the engine had to turn that fast to make enough vacuum to siphon fuel through the idle circuit. Off-idle (of 1700rpms) it didn't pop, bog or stutter as long as you didn't put too much of a load on it right out the gate. But it did idle at 1700 warm. That can make life difficult in stop-n-go driving.


The exact same cam in the exact same engine was an entirely different beast with EFI. You could feather the clutch (as best you can with a Tilton 3 Disc that weight 15# total rotating mass...) and get the car moving from a stop from that 950 curb idle. We actually had it idling down to the 'cranking' parameter---it would reliably fire evenly and keep evenly turning over at 450rpms! It sounded odd, to be sure. But there was no real reason to idle it that low. We did have it at 750 just like stock but we really werent driving the car on the street so a 950 idle speed worked well.


Rough 1700 with the Webers, or smooth 750 to 950 and the ability to load the engine right from the start...that means drivability.


EFI changes the paradigm of 'what is a wild unstreetable cam' should be the title of my post. That was what I really was getting at...

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I'm running a hefty cam in my 13:1 L28 race motor (580+ lift, 280+ duration), with 50mm Mikunis (opened up 44mm with chokes removed), and 11lb flywheel, and I'm surprised that it is actually somewhat drivable on the street (took a little rip up the street the other day). It doesn't idle well below 1200RPM, and doesn't have much power below 3000RPM, but above 4000RPM, it pulls like hell.


I recently picked up an L24 that has never been run, has Arias forged pistons, and supposedly was build as a "race" motor with a "3/4" cam. What the hell does a 3/4 cam mean anyway? :rolleyes: 3/4 full race? What is full race? It has an E88 with polished chambers. Ports look stock. I'll post picks when I pick it up. I plan on just going through it and then seeing what it can do on the engine dyno.

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I got my triples to be quite drivable with the help of a Wideband O2 Sensor.

10.3:1 and haven't been to dyno yet.

Strong enough on power and I just wanted the sound and fury of Triples.


Dialed them in with proper jetting and the AFR is pretty steady around 12-13.5.


... course that was last week and the temp has dropped 15f since then and it rained yesterday so I'll start over today and retune the whole f-ing thing for the entire weekend so I can drive around for 30minues on Sunday. Love em, ya.

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"That's not a fun cruise."


It is if you want an engine to run at 7500 just because it sounds good!


I was taking a ride back from work in Liverpool one evening, and after going some miles I casually asked the driver with whom I was conversing "Change up, Andy?"---we had been buzzing the Clio somewhere between 5300 and 6000 for the past several miles.


"Oh, RIGHT!" (Upshifts to 4th) We continue the rest of the way at 4500-5200 rpms... Clio 1.3's are geared pretty short.


It was 'city traffic' you now, never know when you will have to squirt into that opening or get proper engine braking.


It's all how you were raised, I suppose.

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I also might add, that other than some British Car Rags having a fetish for doing 5th gear pulls from idle, that is a terribly abusive way to drive a car with a small engine.


Really, loading shouldn't be done below 2500 (so oil pressure is built to a decent level) and to even expect a stock engine to "pull" or "have power" below 3500 is unreasonable.


Driven properly the Z is quite a powerful car, but the obsession of people who want a small displacement L6 to pull like a V8 2 or 3X the size is pure fantasyland. You have a 5.7 that pulls from 1500 rpms and dies out by 4400, you would expect that an engine half the size would give similar performance in a power range from 3000-8800. And generally speaking it does in stock form.


By recamming for higher horsepower slightly higher in the rpm range, comparatively you don't lose so much 'on the bottom'...


I've always tried to keep WOT excursions on even my stock Z to times when I have the engine rpms at 3000 or above. It's why first gear is so short in these cars: get into the powerband quickly then keep it there. Yes, I do find myself in third gear at 55mph...or 65mph and consider upshifting.


I didn't buy the car to be a hypermiler. Driving it like this daily on the freeway still nets me 22-24mpg. My highway cruise was 31-3200 rpms. Now with the early box in there it's more like 3500-3600 rpms. Mileage has remained the same, performance feel of the vehicle has improved quite a bit.


For my money, obsessing with power below 3000 rpms is something more for a V8 Grocery Getter, not a sports car!

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"That's not a fun cruise."


It is if you want an engine to run at 7500 just because it sounds good!

I look like a hillbilly driving my 521 down the highway doing 65MPH at like... 4000 RPM or something lol.


I got lucky with my Weber set and didn't need any jet changing and my butt dyno which is worthless told me that it was probably around 200HP. The old 2.8 with the Holset pumping out 12PSI seemed to feel only slightly quicker. Then again I'm doing 3.1 liters. The nice thing about the triples is the accelerator pump. Even in the winter, just pump the throttle a few times and it fires right up.


I do like MonZters 240. Buzzy yet I bet he cruises smooth as can be. B)


Your goal is feasible without being intense and insane! The big guys already told you what you need to know. Just keep reading around and get a feel for all your options.


A reminder for you:

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It is if you want an engine to run at 7500 just because it sounds good!


I don't plan to cruise at 7500RPM; I just want to be able to wind 2nd and 3rd a bit during spirited driving or the occasional track-day and not have to worry about breaking something.


I'm not obsessed with 200HP - its just a stake-in-the-ground to help focus my thinking. If I put a motor together that makes 210 its not like I'm going to back off the timing to hit that "magic" number. On the other hand I don't want to miss that target and spend lots of money for no gain. I've seen lots of stories on the web where someone throws a big cam and triples and a header on a stock L28 and ends up with 150 whp and "a cool lopity idle"; that's what I want to avoid doing...


I do believe that all things being equal, EFI is a better technical solution and I would be just as happy with ITBs as carbs. I'm a little put-off by the complexity: I don't think there is a turnkey setup with the throttle-bodies, control-unit, sensors, pumps, cable etc. needed to put FI on an originally carbureted car. Chasing down parts from different sources and getting them to work together can be a hassle I'd prefer to avoid; that and having triples being something to cross off the bucket list... If there is a turnkey setup out there I might well change my mind.


Thanks for all the info.



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Patton Machine makes an EFI conversion setup for your SU's I believe. You keep the SU body and an injector/adaptor plate should bolt onto the top where the dome/flat top/diaphram thing was. Pricey but it should be relatively easy to install and they give you everything you need from fuel pump, injectors, sensors, to ECU. I've only seen them on Triumphs at my fathers shop but apparently the ECU is programable too. You can buy just the injector adaptor thing for $125 for each SU and do your own with everything else.


Extrudabody SU EFI concept thing whatever you want to call it:



Thread with the SU EFI conversion discussion. Tony mentions Patton Machine:



Link was provided in Tony's post (#2) from the above thread but here it is if you are feeling particularly lazy :D :


Edited by josh817
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