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Old 11-22-2019, 08:07 PM   #1
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400 HP Boxster engine options???

I have a project in mind for a couple years down the road. I have a 99 stock Boxster. Love it! Great car! But it is just under powered. I want to buy a roller S and build a really fast car. I am thinking 400 hp would be a lot of fun! And I am not going to build an M96 motor to that level or spend $30K on it either.

I had originally considered a Chevy LS engine. Cheap, reliable and powerful! But have learned that it is just too big and you have to sacrifice cabin space to make it fit. I am tall so that is a no go option.

I also considered an Audi V8. Nice that it will bolt up to the tranny, but they don't appear to be that tunable nor that reliable. So probably not the best option.

I also considered a Subaru STI engine. They can make tons of horsepower, but again reliability seems to be a problem.

So what is left?? It would seem that many 4 cylinder turbo motors would fit in the car. An Audi or VW would probably mate to the tranny pretty well. But there have to be lots of other 4 or 6 cylinder turbo options that are reasonably priced and reliable that can make that kind of hp.

Anyone have knowledge of viable options?

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Old 11-22-2019, 08:21 PM   #2
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Be careful what you ask for. We had a customer that wanted the same thing, and put the turbo engine out of a front wrecked 996 turbo in an early 986. Even though he was a metal fabricator by trade, and had a well equipped shop at home, what he ended up with was a terrifyingly fast car, capable of destroying its drive line on command, that ended up costing him more that a brand new turbo car would have set him back at a dealer. And when he tried to sell it, everyone ran away screaming because while it was well executed, it was a one off Frankenstein car, that no one knew how to work on. He ended up selling at a huge financial loss.
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Old 11-22-2019, 11:19 PM   #3
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Everything in the Boxster is optimized for the HP and torque that the 2.7l or 3.2l generates. If you do a massive HP increase you will end up with a car that has under-configured brakes, suspension, transmission, etc.

Your best option is to improve air flow into the engine, exhaust flow out of it and an ECU tune. That will give you the best bang for the buck and you won't end up with something ridiculous that will self-destruct and/or kill you!
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Old 11-23-2019, 04:50 AM   #4
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Yes a slippery slope indeed. I did this with a 944, started with a supercharged 3L 986 engine, then LS1, followed by an LS3. The car was fast and fun, but it was constant work and $$$. Brakes were one of the biggest issues for my build, since once you go with an LS, the brake booster no longer fits. This should not be in issue for you, but you will likely want to increase braking (calipers, rotors, etc), especially if this is a track car.

Now, once you are tired of the car, you will likely sell it for much much much less that you have in it. I could not give my 944 LS3 away because it scared the crap out of everyone that test drove it (525 ft lbs and no nannies). I ended up having to part the car to get some $$$ back.

In hindsight, would I do it again? NO.
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Old 11-23-2019, 05:30 AM   #5
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Subaru swaps have been done for near that kind of power:
Subaru powered Boxster "Street Version"
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Old 11-23-2019, 05:54 AM   #6
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I posted this on another post a month ago.
There are some important questions, What year car? What additional parts are you willing to swap out? Anything other than a porsche engine will cost you in engineering or trial and error replacement. 2.5 and 2.7 replacement with bigger engines will take some transmission clutch and axle mods. (I have experience with this). There are three versions of ECU at least, none of which are upward or downward compatible. All require harness replacements or mods, and ECU modification.

If I were to start over again. I'd get 3.4 Engine, transmission, ECU, Imobilizer, harness, Axles, sub-frames and axle carriers from a 987.1. Send out the motor to be sleeved to a 3.8L, with Carillo rods, JE Pistons, rod pins, and rings. Probably $15k to $25K. With the right tune I'd estimate at the wheels dino of 400HP +. The parts would hold up to the abuse and be reliable. They would be direct bolt in with no mounting issues or modifications.

No matter what you decide if you think you can run 300 to 400 hp out of a 1999 Boxster transmission be prepared to replace a lot of transmissions and clutches and drive shafts or drive shaft bolts. The 99 to 2003 use a 8mm bolt on the axles which will not stand up to 300 HP (Truss Me). If lucky you shear the bolt if not you tear the threads out of the axle hubs. I exploded 2, 2003-04 transmissions 3 clutches 3 flywheels. 1999-2002 axles use smaller shafts than the 2003-06, and the late series 2004 and up transmissions and axle use a 10mm bolt. For 325-330 hp I run a 2005-06 S flywheeel. Spec clutch and pressure plate series 2. 2005-06 5 speed transmission. I believe I'm on my 3rd set of axles currently 2005 axles, speed sensors and 2005 bearing support hubs this is the 3rd year with this setup.

In the end almost every part mentioned was just bolt in. Once you change a motor that is longer or shorter be prepared to spend money to trial and error mount, mount supports, cross braces (they have to be there). moving the transmission over a couple of mm will mean shaft angle changes and transmission mount issues. Then mod an intake transmission adaptor. How to mount a starter with a V motor.

I tried to sell mine twice and the offers were all less than a similar unmodified car.
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Old 11-23-2019, 06:41 AM   #7
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jsceash, Great info! Thanks! That is exactly the kind of info I am looking for.

Sounds like a 04 or later S model would be a good starting point. Yes, I know that putting anything other than a Porsche engine in will require a lot of engineering on my part, but I am prepared and capable to do so. I have a lift, welder and metal working tools.

350hp would probably be plenty for me realistically. I want it to be a car I can drive on the street any day, and probably take to a track once in a while to scare the crap out of myself.

I have been researching the Subaru options more. Looks like you can easily get a motor to that performance for 6 to 10K. Also looked at other options. Audi RS 6 engines can be had for $3000 salvage. That might bolt right up. Anything I do will require figuring out making the engine ECU play with the Boxster. But I expect it will stand on it's own and control the engine while the Boxster ECU takes care of the chassis.

I don't really care about resale. Plan to do everything but machine work myself. Just something fun and fast!
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Old 11-23-2019, 07:14 AM   #8
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I think I saw an 06 Cayman S roller on KC CL. He wanted too much $$$ for it ($9K), but you could probably get him to come down. A CS may be a better platform to start with. You might even be able to use the engine as your starting point using JS's formula.
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Old 11-23-2019, 08:35 AM   #9
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ultimately, everything is doable except tires - pretty much impossible without cutting and flaring to get anything bigger than a 285 in the back. which means you can't really get the power down. and a mid-engined car doesn't telegraph oversteer like a front engine car, so you would be backwards a lot.

otherwise, the 3.6 x51 m96 is a 345 hp engine all day long and ran fine in the 996 and well within brake specs - same as what came in the boxster s. the 996 transmission was pretty much the same as what came in the 986s as were the axle flanges iirc.

for options, search the forum - i think you hit all the main contenders; there is a guy who just fit an audi tt 4 cyl turbo, and wizardsmokey is hinting at a proposed swap (my bet is maserati 4.2 v8 ...).

expect packaging and physical connection to be relatively easy, and electronics hard.
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Old 11-23-2019, 04:15 PM   #10
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I've seen a number of Boxster conversions. They all end up costing a lot of money. And the goal of high performance AND high reliability was never achieved. Not once.

But you might be the first.

The upgrades (I don't consider these a true conversion) that work the best are 3.6 or 3.8 flat sixes, upgraded trans, and upgraded brakes. But even something as seemingly straightforward as this can turn out to be awfully expensive.

If I were you, I'd go and talk to everyone and anyone who has tried something like this so you can learn from their experience before you ever start.
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Old 11-23-2019, 07:51 PM   #11
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I'm a tinkerer. I LOVE modifying my cars. (And houses, and motorcycles, and whatever else I can get my hands on)

My own 986 is, well, tinkered. (More on that when I'm done this winter)

But: while I've done many swaps, Frankensteins and bastards in my day, at some point one must ask oneself "why?"

You suggested your goal is to have something around 350hp that's a reliable street car, and that you could take to the track on occasion.

You ever go to the track NOW?

I'd suggest, politely, that if your goal is 350hp, reliably & comfortably, you're much better served by selling your box and getting something else.

If your goal is to play..... to build for the sake of building, then I support that 100%. Just don't be disappointed when it's not reliable OR comfortable. Or 350hp. Haha.

I'd also suggest that, if you're not already going to hpde's and the like, you should be. Trust me when I tell you how satisfying it is to chase- down all those 350hp cars with my little boxster. If you can do that with an underpowered car, then all of the sudden the hp becomes less fun.

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Old 11-24-2019, 05:33 AM   #12
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I always thought the 'S' 3.2 was a pretty good power plant. That the Box with a 996 motor, roughly 300 hp, might be just the right balance. It would still be $$$ to get a good reliable low mileage motor with the IMSB, ect. taken care of.
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Old 11-24-2019, 08:40 AM   #13
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Thank you for all the advise. And there is more to this than just hot rodding a Boxster.

Next spring I am buying a 911. I have wanted one for 35 years and I have the money currently in a savings account specifically for that purpose. Once I have the 911, I will sell my Boxster because I know I will never drive it. Same thing happened when I bought the Boxster. I used to have a sweet BMW 635csi. But once I got the Boxster, I never ever drove it. So I sold it.

I have been looking for a project car for a couple years down the road. Something I can build and paint, take my time on, have fun with and not really care about the final value. I do not intend on putting a ton of money into it, mostly a lot of my own time. I have looked at lots of options, but I have not found anything that really lights my fire. No Mustangs or BMWs or Alfas...... Again, I am going to do this on a fairly low budget as far as project cars go.

But I do love my Boxster! Love the way it drives! Great little car! So it occurred to me that a Boxster Frankenstein project might be a lot of fun! A salvage title, roller Boxster S would be a perfect start if I can find one. I do own a Z-top that I never put on my current Boxster that I would probably install.

Then comes the engine. If I am going to do this, it needs to have north of 300hp. And I am simply not going to do an m96 engine. One of those in my life at any point in time is enough for me. I want something I can drive when it is 20 degrees. (I never drive the Boxster when it is cold because I want the engine to stay healthy) And I am open to the challenge of getting everything to work and have something derivable. It has been done, it is just not easy.

Regarding the engine, I have been reading more about the Audi 2.7t. Seems to be a very robust power plant with all forged internals and twin turbos stock. Very tunable, reliable engine. Worst I have heard is they are prone to engine leaks, but that would be addressed before it was fitted to the car. And they are pretty inexpensive to buy.

Anyway, I am going to build something fast and fun and this is my current thinking. I may change my mind, but who knows.
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Old 11-24-2019, 09:04 AM   #14
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Originally Posted by ksjohn View Post
Thank you for all the advise. And there is more to this than just hot rodding a Boxster.

Next spring I am buying a 911. I have wanted one for 35 years and I have the money currently in a savings account specifically for that purpose. Once I have the 911, I will sell my Boxster because I know I will never drive it. Same thing happened when I bought the Boxster. I used to have a sweet BMW 635csi. But once I got the Boxster, I never ever drove it. So I sold it.

I have been looking for a project car for a couple years down the road. Something I can build and paint, take my time on, have fun with and not really care about the final value. I do not intend on putting a ton of money into it, mostly a lot of my own time. I have looked at lots of options, but I have not found anything that really lights my fire. No Mustangs or BMWs or Alfas...... Again, I am going to do this on a fairly low budget as far as project cars go.

But I do love my Boxster! Love the way it drives! Great little car! So it occurred to me that a Boxster Frankenstein project might be a lot of fun! A salvage title, roller Boxster S would be a perfect start if I can find one. I do own a Z-top that I never put on my current Boxster that I would probably install.

Then comes the engine. If I am going to do this, it needs to have north of 300hp. And I am simply not going to do an m96 engine. One of those in my life at any point in time is enough for me. I want something I can drive when it is 20 degrees. (I never drive the Boxster when it is cold because I want the engine to stay healthy) And I am open to the challenge of getting everything to work and have something derivable. It has been done, it is just not easy.

Regarding the engine, I have been reading more about the Audi 2.7t. Seems to be a very robust power plant with all forged internals and twin turbos stock. Very tunable, reliable engine. Worst I have heard is they are prone to engine leaks, but that would be addressed before it was fitted to the car. And they are pretty inexpensive to buy.

Anyway, I am going to build something fast and fun and this is my current thinking. I may change my mind, but who knows.
Most people admit it is funner driving a Boxster over a 996, with the exception of the power. They have basicly the same engine just bigger cylinders in a 996. My 2000 has it's original engine with 3.6 Litres & it eliminates all the failure prone oe parts, it passes CA smog. If you need to take it to a mechanic or sell it you don't have to write up a special service manual on how to work on it.
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Old 11-24-2019, 04:09 PM   #15
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My S is in the neighborhood of 320 - 330 at the crank with over 282 at the wheels . That combo with the mid engine chassis is a ton of fun to drive . She is tough to handle in the rain but even in the dry can be a handful if I am not careful . Every weak point has been addressed and to look under the hood it all looks stock . If need be any Porsche shop could work on it .

I have driven a LOT of water cooled 996's and some 997's and they are great cars . But they are GT's not sports cars . They are not tossible they are too heavy. But on a highway set the cruise at 100 and they are fantastic. Just my opinion others may disagree . Have fun with whatever whatever you choose .
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Old 11-24-2019, 04:47 PM   #16
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https://kansascity.craigslist.org/cto/d/kansas-city-porsche-cayman/7018033619.html
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Old 11-24-2019, 08:56 PM   #17
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My S is in the neighborhood of 320 - 330 at the crank with over 282 at the wheels .
What's the displacement? Still running factory electronics?

I'm salivating just imagining, Haha.

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Old 11-25-2019, 04:32 AM   #18
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What's the displacement? Still running factory electronics?

I'm salivating just imagining, Haha.

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It is a 3.6 built on my 3.2 block with all kinds of exotic goodies inside care of Jake Raby . Still utilizes factory ECU but with a custom Jake Raby in house tuning program . I could pull more out of it if I switched to his custom cams but I see no need for more power , currently it is a great sleeper and behaves well like starts great hot or cold , good idle , better MPG than stock if I keep my foot out of it etc. in my opinion it is darn near perfect . If I had more disposable income I'm sure the addition of his in house custom cams , a 996 intake system and some playing around with the exhaust could easily get me in the 375 hp arena .
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Old 11-25-2019, 04:58 AM   #19
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Regarding the engine, I have been reading more about the Audi 2.7t. Seems to be a very robust power plant with all forged internals and twin turbos stock. Very tunable, reliable engine. Worst I have heard is they are prone to engine leaks, but that would be addressed before it was fitted to the car. And they are pretty inexpensive to buy.

Anyway, I am going to build something fast and fun and this is my current thinking. I may change my mind, but who knows.
I have a 3.4 996 with 278hp at the wheels in my boxster. It's fun but not enough for me. Most oil leaks on the 2.7 are the oil lines connected to the turbos. It's highly unlikely you'd keep those small KO3's when installing that motor into a boxster anyway. I have a 2.7t waiting to be put in my boxster but I plan on going with a single turbo. Guys are getting 700hp+ out of those 2.7t's. I'm shooting for a more reliable 500hp. I'm not sure the suspension could handle more than that. I also plan on using a cayman 6 speed to make the swap easier. The mechanical part of the swap looks to be very easy. Electrical, now that's a different story.
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Old 11-25-2019, 06:37 AM   #20
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Thanks for the link. The cayman roller would be a fun platform to play with.


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