exercise. On your next in-town
outing with your car, log the time you
drive and keep track of how many
times you lightly accelerate away
from a dead stop compared to the
number of times when you mash the
throttle. Some people drive more
conservatively than others, but unless
you live on a dragstrip, the relationship
will be 40 or 50:1 of light acceleration
versus hard acceleration.
As a further test of this annular
booster concept, we performed a
simple driveability evaluation. We
started with a carbureted small-block
backed with a 4L60E transmission.
This required the use of a carburetor-
mounted throttle position sensor.
The advantage to this was that we
were able to record the exact throttle
position for light acceleration away
from a stop light. After 20 minutes
of light acceleration driving from a
dead stop, we registered an average
15 percent throttle opening on our
standard flange carburetor using
downleg boosters.
We then replaced that carb with
an AVS2 with stock jetting. The
only modification performed on the
carburetor was to set the idle mixture
and idle speed. With those set, we
duplicated our drive procedure and
recorded an average of between 12
and 13 percent throttle opening to
produce the same light acceleration.
While this is not a huge difference, it
does point out that the more efficient
annular boosters did improve the
carburetor’s low-speed efficiency
to require less throttle opening to
accelerate at the same rate.
Currently, Edelbrock is offering
three different size carburetors in the
AVS2 line with a 500-, 650-, and a
large 800-cfm version. AVS stands for
air valve secondary, which describes
the spring-loaded air-valve door. The
Edelbrock carb uses a mechanical
secondary but does not employ a
secondary accelerator pump. At
low engine speeds, if the throttle is
slammed open, the air-valve remains
closed until sufficient air demand from
the engine increases air velocity that
will push the air-valve open. This then
initiates fuel flow from the secondary
boosters.
The air-valve door spring tension
is easily adjustable, and some might
think that loosening the spring
tension would add power at low
speeds. While a slight loosening of
the adjustments might make a minor
improvement, drastically reducing its
tension will only create a hesitation
under hard throttle opening. The
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