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middleagedcrazy

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.

Don

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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.

 

Don

 

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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.

 

Don

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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:

http://www.extrudabody.com/servlet/the-319/Kit-cln--Twin-SU-fdsh-Stromberg-with/Detail

 

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

http://forums.hybridz.org/index.php/topic/85654-su-fuel-injection-manifold-conversion/

 

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

http://www.pattonmachine.com/Pricing.htm#Conversion_components_to_build_your_own_kit

Edited by josh817

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" 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"

 

Boss EFI makes a system meant for cars without a fuel return line especially muscle cars and is a complete Fuel SYSTEM kit involving carb conversion body, fuel pump, sensors ecu etc. It's good to 500HP utilizing an OEM style long and short term fuel trim to 'self tune' the ECU with it's onboard WBO2 for best engine performance with minimal technical involvement of the owner. You can get it without carb body (usually a four barrel, but they do have triple strombergs as an option) to use DCOE Style ITB's. As shown above sourcing of ITB's is from several different sources and is a function of what you are willing to pay. "Turnkey" never comes cheap, and if you think you will bolt on tripples and turn the key to the tune of 200HP we are again entering fantasyland.

 

If that technical complexity scares you, farm it out.

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If you aren't comfortable with EFI, don't use it. Shouldn't be too hard to hit your hp numbers without it. It will make the low speed driveability much better as Tony says, but there is no need to use EFI to get 200 whp, and a 200 whp motor doesn't have to be strung out like a crack ***** to make that kind of power.

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The big take-away that seems to be missed by the OP - we aren't saying you would cruise around at 7500 rpm, or that you can't do it - but rather you don't NEED to do 7500rpm for the goals. You can do it, at a $$$ expense, ok, maybe $$$$ expense..

But what is coming out clearly from your posts is a partial focus on 7500 rpm, or the rpm period, not the power. We live in a world where a Honda can turn 8-9000 rpm and people seem to think if you don't pull big RPM numbers, you aren't really producing big power w/o race gas, 13:1 CR, monster cams, etc... Take a look at aircraft engines for proof of that - but that is not the main point. Decide if you want a set HP, or if you just want a set RPM. While they are related - they are not tied. 200 whp is fairly straight forward to achieve - and with driveability. It won't be cheap, but not much is when your talking bigger power from a 30-40 year old powerplant design.

Again, 200 whp is not hard to do - 7500 is not out of the realm of posiblity, but will drive up your cost for a much smaller gain in power compared to other approaches.

Strokers don't "fall on their face" at 6500 rpm. The Camshaft falls on its face or the tuning falls on its face or the combined setup falls on its face - its not running out of steam because it has a diesel crank and longer rods.

I just bought Dan Baldwin's car that put 255+ to the rear wheels - uh oh, 3.1L stroker, 7000 rpm. The weak point in his,(now my), motor? The cast KA24E pistons. Thats the reason for the approx 7k self imposed redline and honestly it doesn't need any more than that.

I will state - the combo for 255 rwhp was worked on for a long time, uses a no longer available sunbelt prep'd head/camshaft and is a great combo of parts to end up with that power. You can get similar today from Rebello for a price..

Streetable and he drove it to EVERY event he tracked - most of them several hours. Not as streetable as a 175 rwhp car, but I tracked it and it was very easy to drive. Its the combo of parts and the tuning, not the rpm per say.

Bottom line - figure out if its the RPM or the power you want. 7k and 200 rwhp are achievable w/o burning your bank down and knowing super secret know-how or owning super rare parts.

-Bobby

 

 

 

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

know I could get the whp easily with a 3.1 build, but they all seem to max out around 6500 RPM or less

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Scott B. of Group Z Sports Car Club (see photos of his car in the intersection on the 'How to make a 240Z Safer' thread...) ran a Slovers-Ported head with an Iskendarian Cam and SU Carburettors to turn 182HP to the rear wheels on a cast-piston 0.040" overbore flat-topped piston 6500rpms power peak L28 with MASSIVE low-end torque. It's another example of Bob H's example. Originally there was a long list and 'internet overbuild' involved in his car. In the end:

 

SU's man...

 

Now, when he started he was looking into EFI, looking into triple Mikuinis, looking into all sorts of stuff. In the end a set of tired SU's ran that car to 182 and with the power coming on the way it did, a set of 44's would EASILY push that engine to over 200 at the rear wheels.

 

Like Bob H says, there is some obsession with an RPM point. Scott scratches his head when our 2.0 made 205 to the rear wheels. So did someone else when a 3.2 and Mikuini 44's ran 224 at 5800rpms peak! It's the proper matching of parts that makes real power, not som magic bullet of rpms or displacement. What is wanted can be reached using stock components (if not a engine swap from a particular, specific stock Datsun!)

 

This isn't rocket science, it isn't something that needs exotic parts. RPM's will get you power, but at what cost? And why?

 

If there TRULY is a Horsepower Goal---then where you make it won't matter. Gear accordingly.

 

Power in an L-Engine is, has been, and always will be in the Head. RPM's may give you more, but the money you spend on the head in proper preparation will make a versatile bolt-on for almost any combination you choose to run underneath it.

 

Put $3200 in the bottom end and you just cost yourself $3200 for a dedicated setup.

 

Put $1500-2400 into the proper head work and you got something that can work on several subsequent builds, and if you do it right when you get those forged pistons in there later on...it won't be 7500 that is the limit if you've done your headwork right!

 

Believe it or not, we ran the exact same head on a 320HP L28, and on a 205HP L20A. Yeah, we lost horsepower because we didn't have all the compression we 'should' have had on the L20A...but know what? We also didn't want to spend $2400 for another freakin' head, either! <_<

 

That stance has recently changed, though... ;)

 

Street engines and weekend warriors are frequently overbuilt money pits with people building from a list of internet parts everybody says they 'need' when building a performance engine. Many times it's merely "parrot droppings"---guys just prattling on about what you 'need' because they read it in a magazine or online someplace.

 

You can make a LOT of power without spending a fortune on bottom end internals and your longevity will not suffer in any discernable, measurable way.

 

Hell, you want 200HP just go get a stock Eurospec 280ZXT engine....DONE! Stock. Cast Pistons. 300,000 mile reliability.

 

You don't need forged in any 200HP engine.

 

You do in a 7500rpm engine.

 

The two are different animals. There is absolutely no requirement to twist the engine that tight to get only 200HP. It's turning for the sake of turning.

 

And that VO7 7500rpm limit? I'd disregard that as well...

Edited by Tony D

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But what is coming out clearly from your posts is a partial focus on 7500 rpm, or the rpm period, not the power. We live in a world where a Honda can turn 8-9000 rpm and people seem to think if you don't pull big RPM numbers, you aren't really producing big power w/o race gas, 13:1 CR, monster cams, etc... Take a look at aircraft engines for proof of that - but that is not the main point. Decide if you want a set HP, or if you just want a set RPM. While they are related - they are not tied. 200 whp is fairly straight forward to achieve - and with driveability. It won't be cheap, but not much is when your talking bigger power from a 30-40 year old powerplant design.

 

I am the original poster, and I didn't just pull numbers out of the air; I actually did a lot of thinking about what I wanted and my options for how to get there. I wanted to avoid getting into debates about torque-vs-hp and whether dynamic compression is real and such other rants, so I went light on the theory. I'll try to explain my thinking without killing any sacred cows... Before I go too far, let me say this is all approximation; its back-of-the-envelope numbers to get to a starting point.

 

The 200 whp goal is based on having noticeably more power than the RSX-S I drive to work every morning. I'd be happy to get more, but I don't want to sacrifice too much drivability by going too big on cams or carbs.

 

Max crank torque from an NA engine depends mostly on displacement and a little on CR. In a well behaved engine, torque is pretty flat from around 3000RPM up to the power peak where torque starts to drop. A 10:1 CR will generate about 60 ft-lbs/liter (my apologies to the metric purists for those units). Increasing CR by 1 point will increase torque by about 4% (to 63 ft-lb/l) , and dropping it 1 point decreases torque about 4% (to 57 ft-lb/l). You shouldn't assume that trend is linear - as CR goes up it yields smaller and smaller increases in max torque. Again, this is an approximation, but its close for lots of real world engines. Note that the cam doesn't have much impact on max-torque; only on the shape of the torque curve. A big cam can move the point where torque drops off to a higher RPM, and so makes more power.

 

I want to run on pump gas, so a CR around 10 is as high as I want to go. 60 ft-lb/liter * 2.8 liter = 168 ft-lbs . The relation between torque and hp is well known, HP = torque * RPM / 5252. Nothing magic here, just physics. Use some algebra: (250 hp / 168 ft-lb) * 5252 = 7800 RPM! This is a ridiculous redline, but its what you need to turn to actually make 250 crank hp on a 10:1 L28. I don't consider that realistic, so if I want to get close, I need more displacement and maybe a little more compresson. Clearly a stroker build would meet my needs. 60 ft-lb/l * 3.1 liter = 186 ft-lb. (250/186) * 5252 = 7000 RPM. Bump up the compression on a stroker to 11:1 and you can get 250 crank hp at 6500 RPM. I'd prefer to split the difference and shoot for 2.9 liters displacement, a 10.3 CR and a redline somewhere around 7-7.5K RPM.

 

What I didn't say was that a 3.1 can't rev; what I was trying to say was at this hp level (250 crank) the stroker is flowing all the air it needs to around 6500RPM. Reving higher can make even more power, but also requires more flow capability. I suspect the big reason most strokers don't rev past 6500 RPM has nothing to do with long crank throws or rod/stroke ratios; its that they're running 40mm triples and small cams that can't flow enough air to feed 3.1 liters past 6500 rpm. No matter what combination of displacement and RPM you take to get to that hp level, you need a head that can flow the air needed for that power level.

 

Anyways, lots of things to think about - thanks again for the real world feedback.

Don

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