I have done it both ways.

But to answer your question, by plugging the output side of one turbo and charging the output side of the other, you are creating boost pressure in the intake side of your car's system -- basically balancing boost across the two sides via the intake Y-pipe. The same way the turbos do, but just on one side as it's easier that than adding pressure on both the driver and passenger turbos' output sides.

It has nothing to do with the exhaust as the exhaust simply spins the turbo fans to create boost, which you are replacing with pressurized are in a sealed off intake system.

 

wont 20psi blow out the oil seals???

 

I have a quick question. If you had a boost leak that was significant, wouldn't that throw a CEL? I mean, these machines are fairly complex and I would think that the brain could easily detect a boost leak....

 

Yes, usually if a boost leak is so bad it checks a light (CEL), you can also hear it...