<VV> Re: Turbocharging using standard 110 carburetors

[Craig Nicol]

<snip> Does any know if anyone attempted to modify a corvair standard turbo
engine by removing the standard carburetor, and just using an air cleaner,
and then blowing  the  air through 2 standard 110 carburetors by modifying
the tube  running from the  turbo to the intake. I am looking for anyone who
has done it or may have some  pictures of it? <unsnip>

Craig Replies:
As you have seen in the pix, it has been done.  It's commonly referred to as
a "blow through" system and Studebaker used such a system with the
Supercharged Avanti. Frank is right about carburetor and fuel pump
calibration.  I have seen fuel pumps pressurized by the turbo/super charger
but I don't know the physics of how and why that works. There are other
"blow-through" concerns such as spraying pressurized (combustible) fuel/air
mixture out the unsealed throttle shafts and what follows below.

The cleanest way to make it all work is to encase the entire carburetor(s)
in a sealed box and pressurize the whole box or boxes.  This approach
pressurizes the float bowl, which is necessary to promote fuel flow into the
venturi. In a normally aspirated carburetor, the venturi area is below
atmospheric pressure and the surface of the fuel in the float area is at
atmospheric pressure. This pressure difference is what makes fuel flow into
the intake airflow; the jet merely controls the flow. If you simply
pressurize the intake and not the float bowl, you won't have any fuel flow
under boost; in fact, all you will get is a stream of bubbles going the
opposite way into the float bowl fuel.  


The neat thing about a blow through system is that you fit an intercooler
(without the hazards of a draw-through intercooler) and realize substantial
HP gains.  Going to EFI gets around all of the pressurized carb issues (but
brings with is a host of different issues, BTW)
Craig (why not EFI) Nicol