Chevy High Performance – November 2019

NOVEMBER 2019 II CHEVY HIGH PERFORMANCE 25

01 | The AVS2 doesn’t really look any different than older AVS

model carbs except for the new logo, but don’t let appearances

dissuade you. The boosters make an amazing difference.

02 | We bolted a stock AVS2 on a small-block El Camino and measured the difference in throttle position

under light acceleration compared to a typical square flange carburetor with downleg, single-outlet boosters.

Light acceleration was measurably better. This was an early prototype that did not yet display the AVS2

identity plate.

annular boosters. We then duplicated
the test and the engine ran smoothly
and gained over 80 lb-ft of torque at
that same 1,800 rpm. That was our
introduction to annular boosters.
Boosters in a carburetor are those
small, round components that jut out
into each venturi. Their job is to create
a low-pressure area for the main
metering circuit. Here’s how it works.
Fuel begins its passage to the engine
in the carburetor’s float bowl. When
the throttle opens, air moves past and
through the boosters, this creates
low pressure inside the booster. With
atmospheric (high) pressure pushing
on the fuel in the bowls, the fuel
moves through the main metering jets,
is mixed with air (emulsified) in the
main well, and then is pushed out the
boosters and mixed with the engine’s
incoming air.
Standard boosters employ a single,
large fuel outlet. At minor throttle
openings and low engine speeds,
fuel is introduced into the airstream in
large drops, or globs. But large drops
of fuel burn very slowly and it requires
more fuel to vaporize even a portion of
this fuel. Only vaporized fuel actually
burns, some of this unburned fuel
continues out the exhaust, making the
engine run very poorly.

An annular booster externally

appears similar to a standard booster

but employs an annulus, or channel,

to move fuel around the circumference

of the inside diameter of the booster.

Edelbrock’s annular booster uses

12 small, equally spaced holes to

introduce fuel into the incoming

air. These multiple small holes do a

better job of shearing and efficiently

vaporizing the fuel as it enters the

airstream. Oftentimes, this means

less fuel is required, especially at low

speeds, to make the same power.