Stock 944/951 K26 Turbo?

[WydRyd]

Hi,

Can some of you 951 turbo gurus educate me on the K26/6 Turbos?

I'd like to know what their HP potential is like at approx 1.1-1.2bar (~15-17psi) and what their spool-up time is like.

Can you also enlighten me on the K26 turbine codes? I've noticed there are K26/6, /8, /10 maybe? What does it mean? Obviously the bigger the /x number, the bigger the turbine housing, which equals more top end HP at the expense of lag.

Just curious

[Zero10]

Even with the biggest turbine housing available, max compressor speed will still limit the amount of boost you can make.

With the wastegate line pinched off (or in my case disconnected), the max boost a K26/6 will make is 23psi, and after 4000RPM you will see it start to fall off to around 7-9psi at redline. If you want to run 15-17psi, it's adviseable to upgrade the turbo. A possibility is a K26/7 or 26/8. However, a lot of guys are using garrett turbos with great success.
The numbering is as follows K2 - cold side intake area (cm^2) - / - hot side intake area (cm^2). So, a K26/6 has both an intake and exhaust area of 6cm^2. That's how I had it explained to me at least.

With unknown chips, and a fubar'd stock boost management system, I would estimate I was easily clear of 300hp. That's with a peak boost of 23psi in the mid-range, tapering off to about 8psi at redline. It would light up the tires right into 3rd gear, until past 5000RPM. It was just scary fast. I've seen people getting over 300hp at 18psi of boost (320-340hp)

[WydRyd]

Thanks for the response.

Was there anything smaller than the K26/6? Like, a K26/5 or K26/4, for example?

The reason I ask is because I'm looking at a *cheap* twin turbo configuration using two K26's, that will flow 550-600HP all up @ ~18psi boost.

Therefore, response has to be good, which is why I asked whether the K26/6 is the smallest you can get that will flow 250-300HP.

[Tim Hancock]

Zero, what risk of damage do you run by keeping the wastegate closed? This sounds interesting to me.

[Zero10]

Haha, you risk all sorts of disasterous things. I have since realized the impact of these things, and removed all of the modifications done to stock boost control, and run between 11-13 psi.

If you want a smaller turbo, my advice is to go grab 2 turbo's from an 80's subaru with the turbocharged flat 4 1.8L. Those are much smaller, spool much quicker, and are nearly bulletproof. I can't recall what brand they are, but they're very cheap to get/replace as well. Very common turbo's.
If not, go perhaps for a tubo diesel's turbo, one of the VW ones, sized for maybe 1.6 or 1.9L. Those things are built to supply 20+psi of boost for 1.6-1.9L of displacement. Very tough little turbo's, pretty quick to spool up as well. I've seen lots of them going 200k+ miles, running 20psi of boost their entire life. Tough little turbos, and they would be sized appropriately for pairing them up on a 2.5L

Now, back to my setup and problems. The reason things can go so wrong, is if you get just a little bit lean, EGT's will skyrocket, forget a gradual rise, they will just explode upwards. Not to mention, it's already way off the turbo map of the K26/6, which means the efficiency is crap. That said, with a big turbo, and proper mapping (read higher fuel pressure, bigger injectors, etc), 23psi can be achieved relatively safely. With the K26/6, its a miracle that I didn't burn a head gasket, or exhaust valves. But I did melt part of the exhaust system (no lie!), if that gives you any idea how hot things got.

[Lawrence Coppari]

I've got a K27 on mine and have been running 1.1 bar which is about 16 psi for quite a number of years. Mine is a track car so it spends a fair amount of time at full boost. The K27 has over 66K miles on it. For the first 40K miles it was run at 1.0 bar boost. At 140K miles I changed the jet which upped the boost to 1.1 bar. Head is o-ringed, and I do not run it over 6K rpms even on the track. With 95 octane fuel, it will hold 1.1 bar all the way to 6K.

[Zero10]

I had a thought. Don't the turbo audi's (80's era) run a K25/something turbo? That might be sized a lot better for a TT setup...

[nize]

Originally posted by Tim Hancock
Zero, what risk of damage do you run by keeping the wastegate closed? This sounds interesting to me.

there are LOTS of things that can go wrong if you do this cheap 'ricer-style' mod.

basically if you pinch off (or disconnect) the hose between the cycle valve and the wastegate, you can force the car to run maximum boost (determined by wastegate spring pressure).

sounds awesome, right? but wait! there's more! before you do this, you should know what the purpose of the cycle valve is, and why porsche engineers put it there.

the purpose of the cycle valve is to directly control the wastegate (thus, controlling boost). in case the cycle valve fails, the default 'safe mode' is to keep the wastegate OPEN (note: NOT closed). this will limit your boost to .2 bar (also called 'cripple mode' or 'failsafe mode'). there is a reason for this.

basically, the cv (cycle valve) is directly connected to the KLR computer and is the first and last 'insurance' the 951 has against serious engine damage from bad gas, engine knock, detonation, overboost, or the thousands of other things that could possibly go wrong. remove this, and you remove any sort of protection against serious engine damage. i've found that most 951 guys with destroyed engines have removed the cv and tried to bump boost up.

so to recap;

the pro: maximum power
the con: permanantly trashed engine

if you really want more power out of your car by upping boost, tune it the right way by using an electronic boost controller (apexi is popular). don't do it the ricer way by blindly upping boost with disregard to the consequences.

[AaronM]

Nize, I don't quite agree. Properly set up, a manual or other mechanical boost control that bypasses the CV (something like a Lindsey MBC or Guru's ReliaBoost) isn't a risk. It will require more attention and you can't slide by on cheap gasoline like you can with electronic control that will cut out the boost if the engine starts pinging. If you're mechanically sensitive though an MBC isn't a problem.

Of course, electronic control does offer more fail-safes.

Aaron

[nize]

aaron;
i agree that mbc is okay IF you know what you're doing and concurrently properly tune the engine.

my post was referring to zero10 stating he ran maximum boost to 23psi by simply disconnecting the wastegate hose.

[nize]

i just noticed you're near seattle. bring your car out for the local drive on the 8th !

[AaronM]

Originally posted by nize
i just noticed you're near seattle. bring your car out for the local drive on the 8th !

For the record: Definitely and strongly agree that simply disconnecting the WG is a bad idea. (Visions of high-RPM lean-out, blown HG, and other issues are dancing in my head.)

Barring the Porsche gods hitting me with something before then, I'll be there on the 8th. I just got finished putting my driver's side mirror back together after the bolt backed out. Amazing how necessary a driver's side mirror is.

Pay no attention to the stone chips on my car. She's definitely not been a garage queen.

[Zero10]

there are LOTS of things that can go wrong if you do this cheap 'ricer-style' mod

Wow, that's the biggest mis-use of the word ricer I've heard in a while, thanks bud. It's NOT a 'ricer-style' mod, it was something done by the PO to my car, which took me a little while to pin down. It was cut partway from the CV to the wastegate, but left clamped on and ziptied along the way, so unless you actually traced out the entire line, it looked connected at both ends.

[nize]

i know the 'proper' definition of ricer is someone who modifies their car to make it appear fast, not really go fast.

the second-wave ricers however, actually modify their cars to go fast, at the risk of damage. blindly turning up boost is by far the most popular mod among this crowd.

i guess 'backyard engineering' might be a better term for this mod.

did you ever find out what the p.o. was thinking?

[ae1969]

K26/6 ~230-240hp/~260-280lbft
k26/8 ~240-270hp/~290-310lbft

at 15-17 psi

6 will spool up ~2600-2800 rpm for full boost
8 will spool up ~2900-3000 rpm for full boost
Forget the 10

In my opinion MBCs will work well with 26/6, 26/8 and 27 variations.....

If you are using larger turbo I would invest on an EBC. It makes it much easier dialing boost down in the lower gears if you are running +18 psi.

You can always feather the throttle.....but it is easier to just stomp on it....... and let the EBC do the work.

The K27/6 is a great turbo.....a little peaky IMO. The garret hybrids are currently your best bang for the buck. Many configurations and options available..........

[Zero10]

Nize, I just get really grumpy when somebody calls something on my car ricey.

To be quite honest, I doubt this was the PO's work, but rather the PPO's work (or perhaps the 2nd PO's work), since the PO bought the car, drove it for a couple days, got t-boned, and parked it. And the problem there is that she was a woman, so being a man, I am technically incapable to comprehend what she was thinking. Sorry, I drew the short straw on this one, lol.

Anyhoo, I wish I could tell you why it was done. The car was always taken to a very reputable shop in TN, always well maintained, so this one makes no sense to me. However, this would most likely have been done right around the time of the engine swap. So, maybe the hose was cut to get things apart, and was never replaced?...

[nize]

hey, ricey isn't all bad. i've got a *ahem* neon-blue cupholder with night-light LED clipped on to the vent that's rather ricey. and neoprene seat covers with blue stripes to match.

those items are actually functional and get used too.

[Tapage]

OK guys, I like this kind of threar .. very educatives.

Conserving my stock K26/6 Turbo, what kind of mod I can do to get more boost .. more power .. I read in a previus thread, some weeks ago, the most popular cost/benefit upgrade is a Chip ..

Ok .. what is the cons of this upgrade ..?

[nize]

there's a LOT of pro/con (mostly pro) discussions regarding various chips both on this forum and also on rennlist.

that's usually the very first step in the 'upgrade' process, but it also depends on what you want the final product to be. some people have upgraded their brakes and shocks first, some have upgraded their exhaust first, yet others have upgraded their electrical wiring first, etc.

if power is your first objective, the chip will do it.

[Tapage]

Nope in my case .. I thought my first target is look ( interior look restoration ) and reliability of my Car .. I buy it to DD.

Really I like the power .. it's awesome .. but are not my first target, in this way.