[DeTomaso] Edelbrock Performer vs. Thunder Series AVS

[Daniel C Jones]

> can someone explain the differences about the Edelbrock between performer and
> the thunder series avs

I didn't see anyone respond to your post so I thought I would comment.
The Edelbrock Performer is a copy of the Carter AFB.  The Edelbrock AVS is a
copy of the Carter AVS.  The AVS is essentially an AFB with a spring-loaded
secondary instead of the AFB's counter-weighted approach).  The primary side
of the AFB and AVS are very similar and both carbs use stepped rods which
slide up and down in the jets (actuated by a vacuum-referenced spring and
piston).  When cruising, the rod is on the lean step.  Under high load, low
vacuum, conditions the rod moves to the rich step.  The rods and springs are
easily accessed from the top without disassembling the carb.  To get to the
jets you have to remove the lid.  Carter AVS carbs used longer 3 step rods
under a raised cover on the primary side while most AFB's used 2 step rods
under a flat cover.  I'm not sure if the Edelbrock AVS versions uses the AFB
2 step rods or the 3 step but, from a quick glance at their site, it appears
that 2 step rods are used in both Edelbrock AFB and AVS carbs.  3 step Carter
rods could likely be substituted if you used the raised covers.  The rods,
jets and step up spring/piston arrangement serves the same purpose as fixed
jets and power valves serve on a Holley.

The secondary butterflies on an AFB are opened mechanically in response
to accelerator pedal position.  However, a counter-weighted flap, the air
valve, is positioned over the secondaries.  The opening rate and amount
the flap opens is controlled by the airflow demand and the counterweight
resistance the airflow must overcome.  In theory, it shouldn't open the
secondaries until there is sufficient air flow.  One of the drawbacks of
the AFB is that to adjust its secondary opening rate you must add or
subtract material to/from the counter weights.  The AVS, like the later
Thermo Quads and Quadrajets, uses a spring-loaded air valve that can be
easily adjusted.  AFB's use a conventional booster venturi to deliver the
secondary fuel flow.  The AVS (Air Valve Secondary) uses an adjustable
spring-loaded air door that is placed above the fuel-discharge point.
The placement creates a low-pressure area at the fuel-discharge point so
conventional booster venturis aren't needed.  Instead AVS carbs used fuel
spray bars.  Originally, the AVS was only offered as an OEM carb, primarily
on Chrysler products but also on some Chevrolets but Edelbrock offers it
as an aftermarket carb now.  It's also available is a version with
spring-loaded needles and seats (for off-roading).

Dan Jones