Re: Re: Re: Jim Becker

Posted by Jim Becker on December 19, 2001 at 07:47:48 from (4.61.16.38):

In Reply to: Re: Re: Jim Becker posted by Bill Jones on December 18, 2001 at 21:22:43:

I guess one could say that a lot of external superchargers are turbos. But the GM Diesels are a fairly major exception. To say that most,if not all external supers are turbos is probably true in the aviation world.

In the '60s, there were a few turbochargers that got automotive use. The Chevy Corvair and Oldsmobile F-85 both had turbos available from about the same time. The IH Scout was available with a turbo a bit later. This web page:
http://www.corvaircorsa.com/turbo02.html
has a picture and description of the Corvair unit. You can see that the tubrocharger is mounted after the carburetor. That page has a reference to a homemade conversion that put carburetors after the compressor (thus becoming an external supercharger). This page shows it:
http://www.corvaircorsa.com/binnie03.html
If you look at that page, it hints at some of the problems inherent in making that change. The main ones are modifications required to the carburetors themselves. To get by the pressurized venturi area problem that I mentioned in an earlier post, he is pressurizing the carburetor bowl with the boost pressure. Then he had to use a higher pressure fuel pump (with pressure regulation) in order to keep fuel flowing into the bowl. These don't sound that major, but try finding suitable components out of a 1960's standard parts catalog.

The Corvair unit was pretty simple. There was no waste gate. Pressure was limited only by the inherent design of the system. Engine speed had to be fairly high before positive manifold pressure showed. There was no water injection either. A pressure retard was used on the distributor to back the spark off at higher pressures. I don't know much about the Olds or Scout systems, I presume they were similar. The Olds did have a water injection system and probably a waste gate.

There were aftermarket supercharger kits available in the '60s as well. I know there was at least one belt driven supercharger (Paxton maybe) that basicly put the entire carburetor inside a pressurized box. That way they avoided any carburetor modifications (other than maybe jets). But they still needed a higher pressure fuel pump. That too would be an example of an external supercharger that is not a turbo.

The next round of turbocharged passenger cars must have started in the mid/late '70s. At that point, port fuel injection was starting to come into play. So I would guess most, if not all, of those would qualify as external superchargers. Those injection systems could produce enough pressure to not be impacted much by the supercharger air pressure.

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