What Turbo Set-Up On A V Motor In A B6 - Single Engine Bay, Or Twin Rear Mount?

[Nollywood]

Howdy, guys!

As the title states.

I'm building a 4.2 V8 40V, to run boost. Not light pressure, but full-on, so between 14 and 18psi. This will be using the factory C5 RS6 pistons and rods, (I picked up a high-mileage bare RS6 longblock) but retaining the N/A 40V 8-bolt crank. This is all being stuffed into my B6 Avant 3.0 Quattro Sport, running through an 01E 6-speed.

Now, I have 2 options:

Single snail in the engine bay, sitting at the rear of the motor, as in 2.7 STK.
Twin snails mounted at the rear, underneath the deck.

They both have their peculiarities, pros and cons. What would you guys go with, say you were looking at the same set-up, on a 2.7T?

Thanks in advance, for your contributions.

[SleeperAvant]

Sounds very interesting.

Depending on your driveability and power output, what turbo sizes are you considering for each configuration? Single vs. Twin.

[diagnosticator]

I would go with twin low mounted turbos like a 2.7T. I would also cross link the charge air to the opposite bank. IE, the left turbo will feed charge air to the right bank and vice versa. this setup will spool faster than a single larger turbo, and naturally balances the load on the engine. If the left bank is working harder than the right, the right bank gets more boost and vise versa. This balances the load between both banks. This is how large diesels are setup for charge air balancing. The final result is that both banks will produce the exact same amount of torque. The plumbing is a little more complicated, but the load balancing makes it worth the extra complication.

[Nollywood]

Thanks, Diagnosticator. I was hoping you'd chime in, your points are pretty valid.

My primary concern with twins in the 2.7T / RS6 location is heat. The 4.2 V8 40V fills the engine bay of a B6 a lot more, too.

[diagnosticator]

Thanks, Diagnosticator. I was hoping you'd chime in, your points are pretty valid.

My primary concern with twins in the 2.7T / RS6 location is heat. The 4.2 V8 40V fills the engine bay of a B6 a lot more, too.

You can use air ducts to blow cooling air on the turbos. Added heat up top could be a problem too.4" round aluminum duct like used for dryer vents, can be shaped into an oval cross section to clear tight spots, connected to scoops under the car or attached behind the fog light grills.

[Steve Bassen]

Having good diameter downpipes with no pre-cats removes the bulk of the heat that is common with the stock 2.7T turbo setup...

[MoparFreak69]

I'm kinda partial to the big single turbo route.

Only problem is that you're going to have to cut the front firewall out to even fit one, not to mention the crazy plumbing it would take to connect everything. Get the right turbine to compressor ratio and you can make great power and still have good spool times. My current turbine housing is a little large for my power goals with this engine so I'll be swapping in a smaller one tomorrow that will still flow enough for ~550hp but give very usable boost before 3K. The current turbine housing will get me over 600hp easy but doesn't build good boost till after 4K.

[diagnosticator]

Having good diameter downpipes with no pre-cats removes the bulk of the heat that is common with the stock 2.7T turbo setup...

That is very true. Being in the UK running without precats should not be a problem.

[Nollywood]

Turbo service access is important, too. The 2.7T's location isn't ideal, if you need to replace any of the snails, or oil feed copper washers.