924Board.org

[gegge]

Found a SAE paper on the 924 turbo engine. It is interesting to see that the large size of the #6 K26 turbine easily can handle the exhaust gases. The backpressure is well below the intake pressure and reaches 0,7 bar at 5200 rpm.

"In the diagram, fig 21, the results gained from testing a 4-cylinder 2 liter engine are shown. The solid lines represents the torque and the intake manifold pressure, if the wastegate is controlled by the intake manifold pressure. Connecting the wastegate with the exhaust manifold resulted in the dotted lines...as realized in the Saab turbo."

Compared with the larger 3-liter boxer:

"The wastegate, working on high heat load conditions, is passed by about 22 per cent of the total exhaust gas volume at maximum performance of the 911 turbo engine."
_________________
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

[Raceboy]

Yes, and that's why these engines respond fairly well to putting larger compressor on the stock turbine housing.
Of course, the turbine size is sort of requirement as there is no intercooler on 931 and it is essential in order to survive. But apparently it still has its issues.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[Cedric]

Interesting, what SAE paper is that? It seems we cant access papers older than 1998 at work
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[WEASEL149]

Interesting post.
Maybe the Holset 10cm housing I have is slightly OTT then
Oh well, at least I can run some decent boost with it.
_________________
1979 UK 932

[gegge]

# 780718 "Turbocharging Engines for Racing and Passenger Cars" by Hans Mezger, Dr. Ing. H.C.F. Porsche Aktiengesellschaft.

Hans Mezger, the engine maestro of Porsche, ran the Race Car Development Department. During the 1970s, he worked on developing the 924 as a Volkswagen project and then continued on with it when it returned to Porsche’s management. (From Excellence)
_________________
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

[MikeDanger]

sorry but they way i read it, is from another angle. What its saying is the k26 compressor is weak. it drops off pretty fast...... SO of course the back pressure will be weaker.

Lets see how it does with a k27 compressor.... Not so well I bet...

they were, im sure, as usual..... "hey thats good enough, can't be better than the 911"
_________________
It was either this or a giant box of legos

[gegge]

The K26 has a 60/55mm turbineexducer just like GT3076R. The GT3076R has got a 76mm compressorwheel, just like a K27:
http://www.turbobygarrett.com/turbobygarrett/sites/default/files/default_images/turbogroup/catalog_pdf/Garrett_GT3076R_700382-12.pdf

The turbinehousing of GT3076R:

_________________
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

[WEASEL149]

Steve Bassington's first hybrid KKK/Garrett used the smaller number 4 hotside for response and he had no back pressure issues.
'Racing' used the K27 with 6 hotside at up to 2 bars boost with no problem.

Problem with the original KKK's is they're very old designs and so suffer in comparison to modern newer turbos.
_________________
1979 UK 932

[Raceboy]

Morghen runs stock K26/27 hybrid iirc, also numerous 944 Turbo guys.

But agree with Wes, today with the wide choice of modern turbochargers for cheap there is little point in making a´hybrid unless one wants to preserve stock exhaust manifold. And even then it is possible to use modern turbo like Joakim did. Of course it requires bunch of other mods as well but when adding just intercooler and staying with CIS K27 compressor is very reasonable approach and allows to run 1bar boost without choking the compressor like on K26.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[morghen]

[WEASEL149]

[morghen]

I keep telling myself i'll dyno it...maybe this summer i'll have a go.
I need to do some maintainance jobs on it in the spring and then i'll book a dyno session.