Jack W Drews wrote:
>
> Every once in awhile I come up against a question I can't answer. It
> keeps me humble. Since I'm feeling pretty humble right now, please help
> me with this:
>
> On constant vacuum carburetors like SU's and Side draft Strombergs, is
> the piston opening at a given rpm the same whether or not the engine is
> under load?
>
> Stated another way, if my car is on jack stands running at 3000 rpm,
> will the pistons be the same distance up as they are when going down the
> track under full throttle at 3000 rpm?
No they will not. In a fixed venturi carb, there would be less vacuum
under load since you would have to depress the throttle more to maintain
the RPM. In a variable venturi (or constant vacuum) carb, developing
vacuum is used to raise or lower the piston which uses its base as the
top of the venturi. Since the potential vacuum is different, the piston
position is also different. Jarl de Boer
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