How do the twin turbos operate?

[Diesel]

1 per cyl back or are they sequential?

If one per cyl bank, why? Is it to have smaller, quicker spooling up turbos due to only having to cope with gasses from 3 of the cyl's?
When do they run out off puff if so?

Just curious!

D

[KayGee]

Diesel,

S4 uses twin turbos in a 1 turbo per bank configuration. Two reasons, S4 uses V6 engine, seqential turbos would require lots of pipework to implement. In the one per bank basically the pipework is kept to a minimum. Exhaust, turbo, Intercooler, inlet.

The other reason being smaller, faster spooling turbos. After 6K they start to tail off.

HTH

Kaygee

[Diesel]

Thanks mate. Due to all that plastic coverrs nonsense in the engine bay I couldnt see a thing! I guess they are close to the intake manifold each side then, further reducing lag? [Test drive at 15:00 so I can see for myself ]

[Dippy]

Diesel,

They are actually mounted lower down than that. As you & Keygee note, pipework needs to be kept simple because there's not much space in there. Audi opted to sensibly keep the exhaust pipework to a minimum and put the turbos almost literally off the exhaust manifolds. The ICs are low down too (just behind the fog lights), so the intake piping is the longest:

With the bonnet open you can see the air intake on the left, running up to the MAF and over to the top of the engine where it splits into the silver 'Y' pipe. The two branches then run forwards and to the sides, then down to the turbos. The return route is another 'Y' formation literally at the front of the engine, leading up from the ICs and joining at the rubber TBB which joins the two plastic airpipes to the throttle body (lift the front engine cover to see).