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You mean the volute being on the cartridge side of the unit rather than on the cover side?

The flow path through the compressor wheel is the same. It won't care whether the flow path bends left or right (or outward or inward, if you prefer) afterward.

One potential big distinction is that with the discharge being in the cartridge side of the compressor, the compressor wheel can be accessed without disconnecting the compressor-discharge ductwork. In a racing application, ease and speed of assembly/disassembly is a big consideration.

This is an interesting remark about accessibility i hadnt tought of that.

But does the volute position change a thing on efficiency ?

Usually volute curve up ( toward the compressor inlet ) and here it curves down, maybe this have an effect since air may exit the compressor with a up or down component ?

You know like pre rotation vanes have an effect but here itb would be the outlet side.

At the point of exiting the compressor wheel, the flow is very strongly tangential to the compressor wheel and at a good fraction of the speed of sound when the turbo is "on boost". The axial component of the flow direction at that point, with this style of compressor wheel, is pretty much zero. Whether you turn it inwards or outwards in the process of slowing it down, won't matter.

Packaging? Looks quite compact.
Agree with Brian, there is no efficiency benefit.

je suis charlie

Agree with the others - there is zero efficiency impact.

It's done this way on this particular chassis because it allows the compressor wheel, turbine, and bearing cartridge to be removed and immediately replaced without removing the housing from the car. There's a V-band section in the exhaust and intake sides which allows very fast access. Basically 4 v-band clamps and one nut (on the compressor wheel) allow you to remove the compressor wheel in about 60 seconds. Removing the entire housing is much more time intensive.

This is a concern because this is a race car without serious filtering upstream of the compressor wheel and FOD is common. Very rapid replacement of the compressor wheel is a necessity.

The band clamps aren't there primarily for service. We run the Garrett GT-65 turbos on the engines on our tugs. They've been through many iterations of cartridge to turbine housing attachment. The initial was a band clamp design because of the resilience of the connection. There were issues with leakage so Garrett adopted the more traditional bolt and spring plate setup (I don't know the correct terminology here). I don't like this setup because clamp load is lost over time due to fretting of the spring plates. I feel the band clamp system is superior with longer service life but has been cursed by incorrect gasket selection. In my experience the metallic gaskets are taking compression set. This leads me to believe they should be substituted with a creep resistant alloy and the clamping system should not have been changed.

The v-bands I'm talking about in my post above aren't shown on the turbo in OP's pics; they're what attaches the intake to the low side of the compressor and the exhaust to the low side of the turbine. Service speed is a primary concern on these engines; they have basically nothing in common with diesel marine engines.

Don't say that. Our marine turbos are surprisingly similar to automotive units. The Garrets sre simply scaled up versions. The ABB turbos in our fleet are different in that they use diffuser like nozzles instead not volutr but that is all.