Dilberto

Somebody told me that Porsche placed the turbo on the 951, towards the intake side, to provide better cooling, lubrication, and to also create an effect similar to a non-belt-driven supercharger. Can this be possible? I see the intercooled air going straight to the J-boot, which directly feeds into the cold-side of the turbo- which I know is two-stage. Thoughts?

Zach

tyro

Honestly it seems it was the only place they could fit it.

The path goes like this:

Air box>AFM>Jboot>Turbocharger>Intercooler>Intake

xsboost90

i would think the turbo was placed there for room purposes mainly. Also makes cool short IC lines as well.

bearone

i thought the 931 exhaust/turbo on the same side was why it was changed to the intake side on the 951, to run cooler.

87951

xsboost90

yeah im sure they had cooling problems on the 931 with the turbo where it was- you ever try to work on the turbo in a 931! good luck!

chrly924s

I remember when the 931 came out. Everybody was turning them off right after a hard run and frying the turbos. Happened to two friends of mine. Even letting them cool down was iffy, until they can out w/a kit to cool the turbo bearings down after shut off. It was put where it is on the 951 for several reasons, cooling being the main one.

Bill

True.

The 944 turbo location was a direct result of issues on the 924 turbo. The 924 turbo was located on the exhaust side and ran very hot. The 924 turbos had big problems with premature failures due to the extreme heat.

When the 944 turbo was designed, the turbo was moved farther from the exhaust ports to reduce the turbo housing temps. Water cooling was added to the center section (bearing housing) with an electric water pump to feed engine coolant. To help prevent coking of the oil (heat gain in the housing after shut down, cooked the oil into a solid lump which would seize the bearing) the water pump was given a timer that continues to circulate engine coolant at the turbo center section, after the engine is shut down.

As with any design, there are trade offs. Long plumbing runs in a turbo system, increase the time that it takes the turbo to spin to its full speed (turbo lag). Think of blowing up a balloon. It takes less time to blow up a short balloon than it does a long balloon. Thus the 924 turbo design. But if the turbo fails and the customer is unhappy, you get the 944 turbo design.

924RACR

More specifically, the 951 turbo location is a result of the lessons learned on the 924 GTS, GTR, and GTP (which was the 2.5L variant). Note that the GTS IC is the same basic layout as what was used on the 951.

Porsche-O-Phile

Yea I agree it was probably due to space constraints, HOWEVER there is an alternative (which Reeves Callaway took advantage of in his setup) where you put the turbo on the exhaust port (passenger) side, run tight block-hugging headers and the turbo right after that. It's actually quite a slick setup and gets around all the problems of the hot crossover pipe destroying the rear oil pan gasket seal, the loss of energy due to the distance between exhaust port & turbine, etc. The biggest advantage of the passenger-side configuration is the turbo spools extremely fast (full boost by 2,200 RPM is not unheard of). The disadvantage is (as someone mentioned) that there's no water jacketing and it's easy to coke up a turbo if you're foolish with it.

In my setup I'm planning on running an after-oiler to help with this and possibly adapting a water-jacketed turbo to the original setup. As well as allowing the engine to idle for a couple of minutes prior to shut-down.

Porsche-O-Phile

A long run and a cooler exhaust charge by the time it reaches the turbine is also a negative - heat is energy and it the turbine is converting heat energy AND kinetic energy (from the moving exhaust gas charge) into rotational kinetic energy. Theoretically, the hotter the gas, the more energy and the more transfer of energy you'll get at the turbine wheel - although there are obviously practical limits to this.