924Board.org

Nein37 · Joined: 29 Dec 2009 Posts: 513 Location: New London, CT

It appears I've added a .85BAR wastegate spring to my car and the 12.6 psi it achieves is too far outside the efficiency range of the stock turbo. SteveKat has said and I have confirmed that 11.6 psi is the maximum boost the stock turbo can push before becoming a heat pump and inducing detonation.

I have two options, revert to a lower rated spring or upgrade my turbocharger.

I'd prefer to upgrade my turbo. So here is the question.

Where is the best place to get this done?

What are the specs on both the hot side and cold side that will achieve the desired result?

Do I need to provide a core and/or extra parts to make this possible or will the rebuilder source these for me?

Caveat... I've read through the related turbo upgrade threads but they cover so many different options and go off on so many tangents its hard to follow and difficult to cull the needed info. I'm hoping for help from the experts.
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.

Nein37 · Joined: 29 Dec 2009 Posts: 513 Location: New London, CT

It wants a larger turbo.

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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.

Shurick · Joined: 15 May 2005 Posts: 524 Location: Russia, Moscow.

The original CGT used 2660 cold side with 6.10 hot side. Cold side was pretty close to the series II 931 ROW (2664). Hot side wheel is the same, but the turbo housing has lower AR (4.10). All you need is larger housing from 931 mk.1 (6.10) to lower the backpressure.
http://eng.turbo3k.com/catalogue/m-Porsche/
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WBR, Shurick
'79 931 -- intercooled K26-3060-6.10 turbo @ 1.2 bar, EFI+EDIS, 951S brakes, stripped interior, 951 look.
'86 924S -- R.I.P.
https://www.instagram.com/ru_pacecar/

Joes924Racer · Posted: Tue Dec 07, 2010 3:53 am Post subject:

Quicke question isnt there a hot side housing with a cooling water passage. That would cool things.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11732 Location: PacNW

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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Cedric · Joined: 27 Aug 2004 Posts: 2756 Location: Sweden

Or you could do the cheapo edition and get the biggest s1 compressor housing. The difference is very big compared to a stock s2, at least on my s2 engine, moved up the boost about 800 rpm or more, but the boost mid range and upwards is much greater ! I dont remember what its called, 2640 maybe? What compressor do you have atm ?

edit: 2664G4.10 is da shit for more power !
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1980 924 Turbo
www.instagram.com/garagecedric/

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

If you use the complete S1 turbo unit, will that give you even more power ?
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

http://www.924board.org/viewtopic.php?t=22338

Unfortunately the turbine and hot side housing are matched. I.E. you can not just swap on a series 1 hot side onto a series 2 turbine and bearing carrier. I believe that the turbines themselves are two different sizes. This would account for the different spool up rpms. I think you can probably mount up the series 2 to you manifold because the hotside housing should have the recess for the crush sealing ring. It is my understanding that the exhaust manifold mounting flange for the turbo was unchanged for both series. The only changes made to the manifold as far as I can tell is they reinforced it and cut a sealing groove in the bypass pipe flange. I would go get a new triangle gasket and a new crush sealing ring and install that sucker.
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

Shurick · Joined: 15 May 2005 Posts: 524 Location: Russia, Moscow.

s1 used the k26-2470 cold side, which is a bit smaller then k26-2664.

edit: all the turbos from 931 s1 to 937 CGT GTS used the same tubine wheel and shaft. the difference was in compressor size and exhaust housing A/R.
http://eng.turbo3k.com/catalogue/spuse-5326_120_2119/
_________________
WBR, Shurick
'79 931 -- intercooled K26-3060-6.10 turbo @ 1.2 bar, EFI+EDIS, 951S brakes, stripped interior, 951 look.
'86 924S -- R.I.P.
https://www.instagram.com/ru_pacecar/

Nein37 · Joined: 29 Dec 2009 Posts: 513 Location: New London, CT

Harm · Joined: 02 Apr 2009 Posts: 1374 Location: Holland

gegge · Joined: 27 Jul 2007 Posts: 1124 Location: Sweden

Nein37 · Joined: 29 Dec 2009 Posts: 513 Location: New London, CT

Thx everyone. Unfortunately I'm still a bit confused.

Would it be possible for someone to fill in the following, including part numbers and applicable sizing.

US Spec Turbos:

S1

S2

ROW Spec Turbos:

S1

S2

Also, is this the right setup?

http://cgi.ebay.com/ebaymotors/Porsche-924-Turbo-Complete-KKK-5326-970-6406-_W0QQcmdZViewItemQQhashZitem20b55b5f50QQitemZ140481617744QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories#ht_500wt_1182
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.

gegge · Joined: 27 Jul 2007 Posts: 1124 Location: Sweden

Check the link http://eng.turbo3k.com/catalogue/m-Porsche/

All info you need:

Porsche 924 Turbo 145hk
53269706401&53269706404&53269706406&53269706407
93112300404&93112300405&93112301304&93112301305
K26-2664G4.10 Not 100% sure but guessing this is a 931.02 US S1

Porsche 924 Turbo 170hk
53269707000&53269707004&53269707005&53269707007
93112300209&93112301204&931123001200&93112301205
K26-2470R6.10 This is a ROW S1 turbo, small and ineffective.

Porsche 924 Turbo 150hk&177hk
53269706020&53269706022
93112300407&93112300402&93112301301&93112301301
K26-2660GA4.10 Both ROW and US S2 used the same turbo

Porsche 924 Carrera GT 210hp
53269706021&53269706023
93112301201&93112301206&93112300210
K26-2660GA6.10 The same turbo as S2 but a slightly larger turbinehousing.

Porsche 924 GTS 245&275hp
53269707006&53269707008
93112300208
K26-2670GA8.10 Compressorwheel and size of the turbinehousing is almost identical to 250hp 951.

Porsche 924 GTR 375hp
93712300200
K27-2970U16.11 Similar to one of the 748hp Porsche 935 turbos, K27-2970U13.11

Could be typos, but this is what I have figured out so far.
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

Nein37 · Joined: 29 Dec 2009 Posts: 513 Location: New London, CT

Thx Gegge,
So the US S1 turbo is the best choice.

Also, the only difference between my US S2 turbo and the CGT turbo is the larger turbine housing? This seems to suggest that the US S2 turbo should be capable of handling the stock .85 BAR of the CGT. This is what gets confusing... all the literature points to the CGT turbo being larger than the S2 turbo. Can a larger turbine housing make it a better turbo for higher boost applications even if the hot and old side are the same as the S2?

And if the US S1 turbo is the best choice it looks like the one on Ebay may be spot on. My main concern however, is that the turbo on Ebay states it is new. I assume that means NOS which would mean the seals are probably shot.

I'll query the seller to get the lowdown.

Thanks for all the help, its very much appreciated.

_________________
1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.