4.0l 996 with x51, is it possible?

Hi all, I have a 2004 996c4s with x51. At the moment I've been doing little things such as building a set of custom RSR headers/exhaust and GIAC tune. Since I got the car I had this idea that I wanted to keep it n/a but make between 500-600hp (reliably) which I think might be doable since my car sits above 400 as it is with the current mods. want to do something a little different with it than just super charging it or turboing it (maybe I might get the itch down the road who knows) but the sound of an n/a Porsche motor is one of the best sounding cars IMO. Now here is the dilemma, I know there are a few options for going bigger in cylinder size and I'm aware of my options with LN and what not but can it still be done for the same-ish cost as a normal 3.6 motor bump and if so any recommendations would be greatly appreciated.

You’re 5-600WHP NA reliably is the most ludicrous statement I have read in a long time. Congrats.

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I'd sure be interested to hear how you gained 55bhp out of an x51 996. As to making 500bhp or roughly 420rwhp, you're gonna need the gnarliest 4.0 out there to get close. 600bhp....forget it, not happening.

OP - Is your hp figure from a real dyno? Never heard of a 3.6 M96 with X51 runners, tune and 93 octane get more than 360 crank hp. Best M96/M97 builders on the planet only get 3.6L numbers reliably to 370 crank hp; and above 400 (to max of 460ish) at the flywheel with 4.0-4.3 liter bores, massive replacement of internals, porting and exhaust pulse tuning, so I would like to know how you’re getting the ponies. You want to do an LS swap to get your desired hp/tq.

600 isn't realistic but it would be fun to see how high i can get it so that is just a range not an exact, but where i sit now which is in fact above 400, which i am mildly shocked at as well, but where i stand now seeing where im at with what minimal i have done i don't think touching 500 would be unreasonable. its pretty amazing where it is not going to lie, when the vales open up it almost feels like a low boost turbo set up as it stands. it cost money to get something that strong but i know people/have friends that work with this kind of stuff all time time so i can get it done it's just a matter of what everyone else though. bigger radiators is a 100% must and should be happening soon once i put the gt3 throttle body and ipd plenum in as well. if a 3.6L rsr can make 400 as is, a 4.0L with built internals and proper cooling should do the job so i should rephrase, and good suggestions anyone might have would be great and i appreciate the responses so far!

OP - Where’s the data? For a 3.6 liter M96 w/ X51? Not a Mezger 3.6, an M96. Different beast, that Mezger 3.6.

don't we all want a Mezger lol, but the est is from the shop i use which i also cross referenced with fabspeed, it make's either 398-401 depending on perfect temperature outside when it gets cold up here which it is a good bit of the time, in the next 2 weeks i want to do a solid few dyno runs once i put the rest of the stuff i have on and after i get my ims fixed because i got a garage princess before i bought it about a year and change ago. on the x51 note though there is a ton of tuning potential with the variance since a good bit is electronic and if my exhaust scavenging calculations are about right then that should be a very healthy 3.6L GIAC tune- with no modifications besides ECU flash its 10hp which i have a very free flowing exhaust so logically it would be more, lets go on the low side and say it gave me 15 and its GIAC so i dont really need to justify that lol IPD+GT3 throttle body- that's 28hp right there and that's fabspeed certified as well with their testing/dyno gatherings RSR headers/exhaust- 12-13hp which brings me up to that number and no cats as well, i found an emissions place to get me though so i can put all competition pieces and just put some 90 degree cats/spacers

Back to my main question besides the hp figures: is it feasible to have a car with x51 and make it a 4.0L? will that interfere at all or would it be done the same as a non-x51 car?

100 hp/liter is a very efficient internal combustion engine. Beating that significantly requires forced induction or all out racing engines. All out racing engines make crappy street engines. If you think 500 hp from 4.0L naturally aspirated will cost anything reasonable or be fun to drive, you will be very disappointed.

okay so you think it's not worth it to try and get the most out of it and whatever the 4.0 get me leave it as is?

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yes thats feasible. no your car doesn't make over 400bhp. Just added up quoted gains on parts is not how it works. Bet your car dynos at max 300whp

thank you for the clarification but I'm genuinely curious how you came to that number if stock x51 makes 345? keeping in mind that Porsche rates their cars conservatively

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from what i've seen, porsche did not rate m96 cars conservatively...at least those in the 996. I'd say your car probably makes, generously, 370 crank hp (which is what porsche rates it at). When you consider your drive train losses, on a an AWD car, you'd be looking at 20% ish. So, if you do the matter, you end up around 296rwhp. I rounded to 300.

whenever it get to the dyno ill see whatever it makes and ill let everyone know but i probably have just been putting the numbers together wrong the whole time in which case thank you for correcting me, didn't mean to start a hp uproar/sorry for the ignorance per se. Pretty new actually being in the car scene so trial by fire i guess lol. just happy to have an answer about whether or not x51 is conducive to adding a 4.0L

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That�s not how it works. That�s not how any of this works.

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to speak to your original question, i think u will find that a .2l bump is all u want to do in a non-metz motor. Engine builders that have been doing this for years struggle to get 40-50 hp more out if a base motor. Some of this is done by using x51 build logic so im not even sure those gains r available in your motor. i say if u have the funds go for it. Remember that the brighter the candle burns the shorter it lasts.

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Actually it's rated at 345 engine HP. At least that's what the book says. Most people on this forum would be happy with a reliable 345HP, it seems.

so you would say just going to a 3.8L would be better than doing a 4.0L and then whatever that gets me just leave it as it is? just looking to make it a better street car with more life in it, but i also want it to last so that bit was helpful @De Jeeper 3.8L and take whatever i can get from that. would anyone say i'm better off just buying another car at a certain point with how much money i would be putting into it, i.e. a turbo or gt3, something along those lines that come with more powerful motors to begin with?

You might try stuffing a Chevy smallblock in there if you want 600HP. I wouldn�t want a 996 engine to have anything close to that. Even the 996tt guys aren�t pushing too much beyond 480 without serious mods. But then 600+ is possible if you with that engine combination.

The Flat 6 Innovations boys can up it 4.0 liters and suggest, with their supporting mods, that's worth 100 hp +/- over stock. That is probably the closest you will come to a reliable "500" HP M96. It's simple to get 480 HP from a 3.6 Mezger powered Turbo. 550 is not unreasonable. From there, bring truckloads of money and you can have anything you want, 1200 hp is doable. Have you driven the car with it's 345 HP? I'm pretty sure it is fast as-is.

just joined today, looking at doing the same thing on mine but was debating between 3.8 and 4.0, moral of the story is if you want to do engine work on a 3.6 x51 go with a 3.8L over a 4.0L for reliability and longevity? and what numbers should i expect to be making from that?

oh yeah it is pretty quick as is, was just looking for something different than just turboing or supercharging it because i wanted to keep it n/a

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A bump to 3.8 or 3.9 from a 3.6 generally requires no additional head work or flashing, however, if you up displacement you can take more advantage of tune and exhaust mods. A well-executed 4.0+ will use ported heads, bigger TB and exhaust exit, mapping and internal upgrades to push the curve where you want it. Bazillions of posts/threads going back over a decade on this subject. Enjoy the research!

how about the R-Series from F6 innovations? heard anything good with that you've heard

was about to say what the best option from F6 i know @theprf said something about that earlier

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Perhaps my grammar let me down there. I mean porsche and every other manufacturer rate their horsepower at the crank, not the wheels. I was not referring to the number but rather the units

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If your 996 C4S is a �forever� car...sure! If not, sell it and buy a 997 turbo for the same money.

Over the past 7 years I’ve probably watched 30-40 m96 race-prepped engines go across the dyno (my racing club, POC, is power/weight so we’re always interested in other competitors numbers ). X51 m96’s pop 315-325 consistently. No, your motor is not making 400bhp. It’s probably around 310 w the GT3 throttle body. Vision has built a ton of 4.0 m96/97 engines. They put down 385bhp.

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You Tube

we're all just beating a dead horse at this point lol, but F6I seems to be the best way to go to make solid power, nice touch they make the case red too

That's very funny if you want to make your car faster for small dollars - make it lighter

You need to call Flat Six Innovations, they have some in stock.

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Don't forget he's in Colorado!!

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^^^ If nothing else, Jake will give you the straight poop - you can count on that.

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Sometimes people need a strong dose of reality...if they can handle it.

If you have a 2004 C4S with X51 I would believe that is a fairly rare setup. I don't see them very often with X51. I'd keep that baby stock and enjoy it. If you are looking for more, buy a turbo and all of your fantasies will be realized!

I'm genuinely curious what one would be doing with 500-600hp. Are you building a drag strip car? Even for track work, and this might depend on the track, but more power doesn't always equal faster. About 300hp is plenty to have a good time on the street or back roads without ending up in a ditch or in jail.

This guy is trolling everyone! Doesn't have money for any rebuild let alone a high displacement one.

I wonder what brand of oil he would use?

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@ltusler I think you can confirm that we've been offering a 4.0 built from a factory X-51 since 2008 :-) I can apply the X51 parts to our engines as large as the R44, BUT only if someone wants less power than our R51 CNC ported heads will produce, on the same engine. No, we don't have engines in stock, Our first availability of an engine completion is currently February of 2022