[DavidRoss]

I’m in the early stages of researching the K20 for a Porsche Boxster swap.
Current motor makes 290hp @ 6200 RPM with 230 ft-lbs torque NA.
Id like to improve that to 300-325hp and 300ish ft-lbs at to more than 7000 RPM.
The car is a daily driver / Road trip car. 95% of its time is under 5K RPM.
Reliability of the drivetrain is a priority and the reason for the swap.
Id prefer a supercharger to avoid lag or a smaller turbo that spins up quicker knowing I’ll lose out on top end which I rarely use.

Is a reliable 325hp 300ft-lb 6500RPM K20 reasonable with stock internals?

 

[SaucerClone]

that is EASILY doable, the stock internals on most K20s will go up to 500 wheel as far as I'm aware. the transmission (if you've swapped that in as well) holds up to around 400 whp stock, but below that, I've not heard of any real issues aside from the obvious clutch upgrade.

a few questions for you though: have you already made the swap yet, or is the engine sitting in a different car right now? that power and torque figure NA is really impressive and I would love to know how you did it without doing a K-hybrid

 

[DavidRoss]

It's one thing to easily 'go up to 500 wheel' and it's another thing to do that reliably. Not reliably get me through the weekend burning tires but 100,000 miles and I haven't had a major breakdown.

The NA numbers I gave is what the car does now with the 3.2L 6cylinder boxer motor that I want to replace.
edit: s/3.3L/3.2L/

 

[Lotus]

any charge cooled MP62 supercharged K20a2 will do that. CT-E or a DC5 JRSC.
Or get a Rotrex SC and stick to some 10-12PSI. Kept the limiter to 8500 and get a GOOD mapping.
GB won't be an issue as you'd have to use the Porsche GB anyhow.

 

[DavidRoss]

Thanks. I'll start reading up on the MP62.
I got the idea from @tuningbynick who is making a swap kit.
It will use a Honda GB vs the Porsche GB. Everything fits better and axle shaft angles are better.
I'll need to see if there's room for the MP62 but there likely is.

Do you know of any Dyno charts for a K20a2 and MP62? 8500 RPM is a lot higher than I wanted to go.

 

[SaucerClone]

The NA numbers I gave is what the car does now with the 3.3L 6cylinder boxer motor that I want to replace.

My mistake, I thought you had already swapped in the K20 :/

Have you considered getting a K24a2 or doing a K20/24 then? the k24 is significantly torquier and will fit better into your low-revving model

 

[DavidRoss]

Have you considered getting a K24a2 or doing a K20/24 then? the k24 is significantly torquier and will fit better into your low-revving model

The K24 is 3/4" taller than the K20 which might give issue with alignment. The Boxster doesn't have a lot of vertical space. A Cayman would fit a K24 without issue but the convertible top gives me a hard height restriction.

I'm in the research phase so I wouldnt rule anything out. The K20/24 would use tuningbynick's kit once/if he develops it so, I'm researching what an engine would look like with his kit.

 

[Lotus]

I'd keep the Porsche GB. Saves you drive shafts etc.

Turbo Honda K-Series swap into my Porsche - Rennlist - Porsche Discussion Forums

Rennlist Canada - Turbo Honda K-Series swap into my Porsche - Hi Everyone Thought id share the progress of my 997 project So i have this 2006 911 Carrera S and basically i was bored of the power. I own a dyno and tune cars here in Toronto and have lots of Honda clients making 500+ HP...

rennlist.com

For a heavy car, I'd go Rotrex. On the k20, they are nuts.

 

[DavidRoss]

I'd keep the Porsche GB. Saves you drive shafts etc.

Turbo Honda K-Series swap into my Porsche - Rennlist - Porsche Discussion Forums

Rennlist Canada - Turbo Honda K-Series swap into my Porsche - Hi Everyone Thought id share the progress of my 997 project So i have this 2006 911 Carrera S and basically i was bored of the power. I own a dyno and tune cars here in Toronto and have lots of Honda clients making 500+ HP...

rennlist.com

For a heavy car, I'd go Rotrex. On the k20, they are nuts.

The 997 is a rear engine car with lots of room to fit the K20 inline. The 987 is mid engine with very little room and the axles already angle aft quite a bit with the stock motor and GB. The K20 would have to move the GB even further aft, making the axle angles even worse. This is a common problem in doing swaps in this car. To keep the GB in the same location, you need to cut the firewall and move the seats 3 or 4 inches forward and leg room is already tight for me.

If I could fit a 4cylinder inline with the stock GB without cutting the firewall, I'd be swapping for a Cadillac CT6 3.0L Twin Turbo but it's just too much cutting and leg scrunching. Which is why I like the transverse K20/24 so much.

Is 3,000 pounds considered a heavy car for the K20?

 

[Lotus]

I use a supercharged k20 in my Elise. It weights half of that


Then it seems you only need to decide what type of power delivery you want.
Easiest would be a MP62 supercharger, uncooled. 300HP, 8500 rpm on a k20a2
next would be a charge cooled MP62, good for some 350HP. Non are available new anymore.
Current options for roots blowers are Mercracing's TVS1320, 1900 and 2300.
Then there are the Rotrex blowers and then of course turbocharging.

You'll probably need to spend a couple of days reading here. Nearly everything was done before and posted here.

 

[DavidRoss]

I use a supercharged k20 in my Elise. It weights half of that

That's a really light car.
Would like to hear about how you have the K20 setup and your likes/dislikes

 

[Lotus]

it is a mild k20a2 build with a CT-E supercharger, currently no charge cooling.
steel rods, Mahle forged pistons, 11.5:1 CR, Toda A3 cams & springs. Revs to 9000 rpm.
Gearbox is a NPQ3 from an EP3 Civic Type R with a 3.9 final drive, Wavetrac LSD and shorter 4th to 6th gears from the JDM DC5 Integra.
I'd prefer a smaller gap from 1st to second and 2nd to 3rd gear. Next time I see an affordable Gear-X come up for sale, I'll be tempted. But it is only a nice to have.

On track is it nice and I use 2nd to 5th gear. On the road, this setup gets me to drive with very low rpm. In order to get some serious shove, I need to switch gears. Overall this combo only gets alive past some 60mph.
A k24 would offer way more torque, but won't rev that high.
Maybe I drop the SC again at some point.

A friend of mine tracks his k20a2 with a JRSC and about 300HP for more than 12 years now. Never opened the engine. Complete stock.

 

[gtimportfanatic]

Any turbocharged K20A2/z1/3 will make 350+whp reliably with less than 10lbs of boost with a 55-58mm turbo. As for turbo lag, it’s really a non factor in today’s age, some of the old narative about how they perform is basically done. Another thing is, regardless of how you drive, for low down grunt you will not replace displacement, a K24 in any iteration will always feel better driving around in the below 5000rpm drives

 

[mvmisha]

Any turbocharged K20A2/z1/3 will make 350+whp reliably with less than 10lbs of boost with a 55-58mm turbo. As for turbo lag, it’s really a non factor in today’s age, some of the old narative about how they perform is basically done. Another thing is, regardless of how you drive, for low down grunt you will not replace displacement, a K24 in any iteration will always feel better driving around in the below 5000rpm drives

How the k20a6 or k20z2 will usually perform with similar turbo setup? There's not much info about those, and they are quite cheap in europe.


In my mind they would perform similarly to the k20a3, but that's just a guess.

 

[LotusElise]

How the k20a6 or k20z2...In my mind they would perform similarly to the k20a3, but that's just a guess.

My mind shows similar guesses . Those share on a wider bandwidth the same hardware. Here and then the casting was slightly changed, IM may differs, ECU definitely differs because of different emission certification level and so on. But the longblock should be quite similar.

 

[mvmisha]

My mind shows similar guesses . Those share on a wider bandwidth the same hardware. Here and then the casting was slightly changed, IM may differs, ECU definitely differs because of different emission certification level and so on. But the longblock should be quite similar.

Yeah, that's true. I wasn't taking into account IM, headers, etc.

 

[gtimportfanatic]

How the k20a6 or k20z2 will usually perform with similar turbo setup? There's not much info about those, and they are quite cheap in europe.


In my mind they would perform similarly to the k20a3, but that's just a guess.

I generally sum it up to, if its a 3 lobe cast head with. “True” vtec, the same results will be had in the horsepower chase