Quote:
Originally Posted by Christ
How would a single VGT create more airflow than a setup where one turbo is activating another one? VGT's don't serve that purpose... they are basically there to keep specific boost under varying conditions.
My idea involved spooling the first (smaller) turbo off the engine, and using it's spooled (compressed) air, obviously a much larger CFM than the exhaust flow, to spool another turbo's exhaust side, before going into the engine. The secondary turbo's compressed air would then be fed through ducting into the wake at the rear of the vehicle, hopefully eliminating part of the wake.
Through the feedback loop that standard turbos use, this isn't really possible though. The secondary turbo would never reach "full spool" and thus, wouldn't create the kind of airflow it could otherwise achieve.
Also, a turbo won't spool properly without more airflow than it's host engine can achieve, hence the reason for "turbo lag".
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In terms of wake infill there isn't much that can be filled, so to speak, at reasonable speeds. And regardless of how many turbos you use, the maximal amount of infill will only be however much exhaust gas the engine is putting out.
If going for peak power a twin turbo (or twin charged) setup can be advantageous, but in terms of efficiency they'll still have inefficient portions of their compressor maps that they operate in. I suppose you could overlap those inefficient portions, but by then you might as well just go w/ a VGT in the first place and not add the extra weight/complexity.