by Jon Mikelonis
A few short days after FordMuscle announced the acquisition
Redneck, we received numerous emails from experienced
offering truck-specific tips and advice to the staff. In more
than one instance, FordMuscle was advised to resist running
a Holley if we planned to do anything more than dump-duty
with the 1978 F250 4x4. You have to respect the insight of
the FordMuscle readership because these guys obviously knew
that FM's focus on street machines and nothing more than a
freshman orientation in the world of off-roading, might cause
us to make some mistakes. Unfortunately, those emails came
a little too late. In the article First
Load, adding a remanufactured 600 CFM Holley double pumper
was among our initial upgrades. While we never had a chance
to test it off-road, the carburetor proved to be a mediocre
solution even on the street. The shear weight of the F250,
combined with the underpowered 351M had us starting in first
gear around town just to maintain a signal. If you are at
all familiar with these trucks, you'll know that first gear
is reserved for pulling stumps out of the ground, not pulling
out into highway traffic.
Workarounds do exist for standard Holley carburetors that
make them better off-road performers. Adding extensions
to the vent tubes and incorporating the Holley vent
whistle to the metering block(s) are just some of the
common tricks for four-wheelers running Holleys. We'll cover
those options at the end of this article. Either way, when
Holley offered a Truck Avenger to FordMuscle to test on Project
Redneck, we gladly accepted the offer and requested the smallest
carb of the series, the 470 CFM model.
Flood-Free duty on inclines and nose-down descents is where
the Truck Avenger is designed to showoff its most unique benefits.
On some beginner backroads in Northern Nevada, we tested the
Truck Avenger at a 30 degree descent. As the video below shows,
our F250 maintained an idle and showed no spill-over during
Project Redneck and The Holley Truck Avenger In Action
How Does it Work? Key Features and
Benefits of the Truck Avenger
The Truck Avenger uses Holley's most off-road friendly carburetor
design as a foundation and adds a few key features that make
it off-road full-proof. Vacuum secondaries and side-hung floats
are not unique to the Truck Avenger, but both are advantageous
for trail use. By nature, side- hung floats are more resistant
to bouncing and control sloshing in the bowl better than center-hung
floats. Vacuum secondaries delay fuel metering until sufficient
engine speeds are reached. Since many off-roaders spend a
great deal of time at low engine speeds, vacuum secondaries
are preferred. A vacuum actuated secondary helps prevent the
bog effect sometimes associated with carburetors equipped
with mechanical secondaries. This can be especially important
when climbing out of a hole.
So this brings us to what makes the Truck Avenger unique.
While the list of features and benefits from the manufacturer
is long, the three key components of this carburetor series
according to FordMuscle are its...
Block with Integrated Check-Valve in Main Well
Loaded Needle and Seat
After running Project Redneck on a few trails and around town
for a month or so with the Truck Avenger installed, we took
the time to pull the carburetor off and get it on the bench
for a close-up.
The Truck Avenger just looked appropriate on top of the
351M in Project Redneck. Other than the one-piece vent
tube, the Truck Avenger appears to be a standard Holley
4160 carburetor at first glance. However, it's not a 4160,
the Truck Avenger is a 4150 with vacuum secondaries, electric
choke, side-hung float bowls, and metering blocks with
replaceable jets on both the primary and secondary sides.
Without question, the "sexiest" part of the
Truck Avenger is the one-piece vent tube. With a standard
Holley, extreme angles can force fuel up the vent and
straight down the venturis. This "crossover"
tube prevents that from happening.
To see for ourselves what made the Truck Avenger tick,
we cracked open the primary bowl.
Take note of the spring-loaded needle and seat and the
baffle. Both are used to provide good resistance to fuel
moving in the bowl. The spring-loaded needle and seat
is especially important during a high-speed trail run
on rough terrain.
While the 470 CFM Truck Avenger is jetted for small motors,
it also works well for an underpowered stock 351M. The
470 CFM Truck Avenger comes equipped with number 57 jets
in the primaries and a 2.5 power valve. The combination
turned out to work quite well for the F250.
Hello? No that's not a new Holley cell phone, it's a metering
block with something rattling inside. That rattling is
from the Truck Avenger's exclusive check valve that is
integrated into the main well. The check valve prevents
fuel from flooding out the boosters on an extreme incline
Avenger main well check valve. It's in there, take a listen.
Off-roading with a heavy vehicle requires a carburetor
that supports great low to mid-range throttle response.
The Truck Avenger uses "High Vacuum Signal"
annular boosters in the primaries. By design, annular
boosters create a venturi within the main venturi to create
The Truck Avenger comes with site plugs for setting the
float level. These are not intended to remain in place
and should be replaced with the standard brass plugs once
the floats are set properly.
For a complete run-down of features
according to Holley themselves, you can see the Holley
Off-Road Truck Avenger series at www.holley.com.
Do-It-Yourselfer's Make Their Own "Truck Avenger"
As we mentioned, off-road enthusiasts have been implementing
some of the Truck Avenger's features long before Holley decided
to market the product. While it would take some serious work
to fully convert a standard Holley to equal the Truck Avenger,
a few modifications to your Holley may satisfy your personal
off-road requirements. Jody York, a technical contributor
offered FordMuscle these DIY tips for those willing to take
on the task.
For more information on the tips shown
here, see Off-Road
Tricks for Holley 4 Barrel Carbs by Jody York at www.classicbroncos.com.
Small 470 CFM Truck Avenger Performs 'Round Town
Summon your peers about the right-sized carburetor for your
and you'll get a wide range of opinions. In this hobby, with
age comes wisdom and the wise can confirm that there's something
valid about backing off your tendency to go with big carburetors.
It may seem that a 470 CFM Holley is tiny for a 351 cubic
inch motor but that's where the standard carb formula lead
us when choosing from the three available Truck Avenger carbs.
According to Holley, the 470 CFM unit is best suited for 4-cylinders,
V6s, and V8s under 334 cubic inches even though it worked
well for our larger displacement application.
Computing the standard carb selection
formula for Project Redneck we arrived at a figure of 406
CFM. We came to this result using 351 cubic inches, 5000 RPMs,
and a volumetric efficiency of 80%. Most stock, production,
low performance motors fall between 75% and 85% in volumetric
efficiency, so 80% seemed to be a conservative figure for
this our "M" motor.
In this case, experience paid off providing us with great
drivability around town and adequate throttle response even
with the stock 351M. Besides, at $3.50 a gallon, we could
use all the help we could get.