Bi-Turbo with vacuum operated VGTs - can I do it?

V3 BETA TESTS
1

Gents I’m not a turbo guy, but I need to make recommendations on choosing some parts for air-cooled 911 (flat 6).

The idea is to have two small symmetric turbos boosting roughly up to 0.5bar and NO Intercooler that would spool very quickly.

As this is flat-6 this basically means I will have TWO 1.8-1.9L 3-cylinder engines connected at the crank and maybe at the muffler, and each of them with own turbo.

Would I be able to drive those two VGTs with Black V3? Closed loop operated PWM vacuum valve? Two of them?

If not Black V3, then what, PRO?

Thank you.

2

The main question is, will there be a common plenum?

Because if not, you need two MAP sensors and two independent boost controllers.
We don’t have that yet in any ECU.

Perhaps you could create a custom option in PRO, but that’s not ideal.

If the plenum is common, you control both turbos identically.

3

It might be possible at this stage, but then for the under boost conditions I’d need to operate resonance chamber.

Engine is to be a mix of highly effective N/A and small boost.

There will be 6-butterfly ITBs for sure.

4

Just thinking… VGT allows to change how much boost vs rpm (simplification) each turbo gives. With common plenum in theory one turbo can blow a lot and other just a bit and no-one would know?

On the other hand a common plenum would work as a fail safe for such situation, spreading the boost evenly.

Assuming both turbos behave (almost) the same and these share the same plenum - only one PWM controlled valve would be needed to control BOTH VGTs (vacuum hose splitted into 2) based ona closed loop feedback.

Would that be advised setup? No issues in such config with Black V3?

5

That is a possibility.
That’s why you either have everything separate or everything in common.
There is no point in independently controlling turbos if the plenum is common.

That’s precisely what I suggested.
Use one signal to control both turbos.
You can split an electric signal or a pneumatic one.
I don’t see any issues with either of those solutions.

6

The drawback of single plenum is more volume in it. Therefore a bit more lag, and that’s what we don’t want.

7

Is e-controlled VGT preferred over vacuum one?
How to split electric signal, isnt there feedback signal as well?

Sorry for dumb questions :slight_smile:

8

I have no experience with VGTs, so I’m unsure which control method is preferred for that system.

With MAC valves, you can connect two in parallel to a single output.

With an electric actuator, you need two independent motor controllers.
This can be achieved by controlling one actuator with the electronic wastegate mode in the boost controller, and the second actuator can be controlled using a custom DC motor strategy where the target position is the same as in the boost strategy.