924Board.org

[ideola]

I've read thru a bunch of the KKK/K26 posts, and even looked at the compressor maps...but I have no idea how to interpret them...and I can't seem to find anything that notes the CFM produced by the K26.

I've read elsewhere that a turbo needs to produce ~150 CFM for every 100HP produced by the engine. So for my stroked, overbored, overboosted wide body project, I'd like to target north of 300HP, which would require 450+ CFM. Anybody know if the Series I K26 can produce that CFM? Otherwise, I may be looking at a K28 hybrid.

On that note, are all K28's compatible with the K26? Is it just a matter of getting the compressor housing, and rebuilding the K26 unit with the K28 hotside? I looked at Raceboy's post on the subject, but there weren't alot of part number / details provided there.

TIA
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erstwhile owner of just about every 924 variant ever made

[-nick]

I can all but guarantee the stock k26 won't support 300hp. I still need to check into the details of what Majestic did to my k26. I can see that the compressor side is extrude honed. I imagine they changed out the compressor wheel also. At least I hope so as part of the $800 rebuild+upgrade...

I think a k28 is overkill for anything except very large and peaky dyno numbers. I believe some of the 951 folks are cracking over 300rwhp with the k27/6 which would deliver much more usable power. I would look to that first. There are a couple different k27 compressor wheels to choose from though, so do some research.

ps- you'll have to leave the hotside stock, it's the compressor side that allows for upgrades
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

[ideola]

So I've been doing some research, aided greatly by my brand spanking new copy of Corky Bell (thanks to my lovely wife, who bought it for me for my b-day!). I've found some compressor maps, and looking at the formulas in Mr. Bell's book, there is no way the K26 stock setup (SI or SII) will achieve the power output I want with any degree of efficiency. So, I need to build a hybrid.

However, I'm not clear on how to actually complete a hybrid K27/K26 setup. The stock 931 K26 setup has the intake additional plumbing and the housing for the compression spring & piston (what is the function of that mechanism, anyway???). The K27 units don't have all that stuff, so how do you take a K27 with all the missing stuff and hook it up? From looking at photos of K27 cold side housings, I suppose one could put together a tube with silicone elbows that would go from the air box to the turbo, but what about that compression spring and piston business?

Also, will any K27 pretty much bolt on? So, I could use a K27 from a 930? or an Audi? Still looking into the differences between the K27 7006 and 7200...
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erstwhile owner of just about every 924 variant ever made

[Rasta Monsta]

I don't believe the K27 shares our unit's 3 bolt flange. The piston, etc, is a recirc valve that keeps the compressor from stalling when the throttle slams shut. Other apps have different approaches to this problem, but CIS doesn't like metered air venting to the atmosphere.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[ideola]

[Cedric]

Can this be an option ? It´s a nice solution to be able to use more modern turbos. There happened a lot on turbocharging in the last 30years


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1980 924 Turbo
www.instagram.com/garagecedric/

[bass gt]

[ideola]

[bass gt]

Q. With the changing of the turbo, are you keeping the CIS or going EFI?? I don't think the CIS will support the HP you want, so EFI is the smartest route. Then the BOV operation becomes a moot poit, as the air is no longer metered, it can't go rich.
As for the turbo, it is a series 2 turbine, mated to a 30 series centre section, and a 28 series compressor. Bit of a frankenstein, but it works.
Not cheap to do, but when you facor in the ease of keeping the original manifold ect, it works out OK.
If you have any questions, drop a line to Turbo Dynamics in the UK. hey built my unit, and might be able to give you some ideas.

Steve
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Front Wheel Drive is the Devil's work.

[ideola]

[bass gt]

OK,

So if you are keeping the CIS,you need to vent the intake air from behind the throttle plate, back into the air intake system, but between the fuel head outlet and the turbo inlet. Tricky, but not impossible.
FWIW, and i guess you know this already, but may i offer a bit of advice??
In terms of cost and developement time, i think you would be much better to go over to EFI once you start upping the boost. EFI offers so much more in terms of reliability and control. If the CIS starts to lean out, you will have no idea until you are looking at a big engine rebuild.
I would use the CIS to run the motor in, just on stock settings, and start getting the componenets together for the EFI.
The CIS fuel pump is plenty man enough for the job, but the rest will not work. Much better to prove the motor is basically good, and then change over in one step. Much less painful and costly. The last thing you need is to bang the motor on a trial CIS system.
Just my 10 pence worth you understand

Steve
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Front Wheel Drive is the Devil's work.

[Rasta Monsta]

BTW, the "funky" elbow goes to the intake manifold. . .that's where the vaccuum comes from that operates the valve. I would think you would need to be careful about venting boost into the tubing between the metering plate and the turbo inlet, as the metering place (and hence, mixture) could be effected by the pressure. If that were the best way to go, Porsche might have used an external BOV instead of that expensive casting.

Your time may be better spent tuning your EFI setup. . .
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[ideola]