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34 CAR CRAFT NOVEMBER 2019
Swapping out the high-speed air bleeds (the
two inner restrictors on both sides of the
top of the carb) for smaller units restricts
the air that can mix with the fuel to
emulsify it. Because there isn’t as much air
mixed with the fuel, it automatically richens
the air/fuel mixture through that circuit.After bringing the jets up to 102 in the front
and 105 in the rear to provide enough fuel
at WOT, the engine would go dead rich at
steady-state part throttle. To fix this, Senior
from Prestige Motorsports had to find other
ways to provide enough fuel while also
bringing the main jets back down in size.
The first step was to balance the barrels
front to back. By moving the linkage to
the first hole and taking out the slop, the
secondary throttle blades opened just about
at the same time as the primaries, evening
out the flow through all four barrels and
dropping the air speed in the front two
boosters.the engine at 2,500 rpm and slowly
adding throttle. This simulates a com-
mon situation in automobiles like riding
down the highway at 60 mph in high
gear and giving the engine more throttle
to maintain speed as you go up a hill,
only to have the engine fall on its face.
The fix for this isn’t as simple as a jet
change, but a fix is definitely possible.
Senior explained that the idea is to add
fuel through other means so you can
swap in smaller main jets (which are
more resistant to booster tip). He
walked us through these steps, testing
each on the engine dyno until he got
the results he wanted.BALANCE THE
BUTTERFLIES
One way to reduce the chances of
booster tip is to lower the velocity of air
through the boosters. Going to a larger
carburetor isn’t always the best idea,
but there are other options that can
help. This engine is using a 1,250-cfm
Holley Ultra Dominator double-pumper
carb. Most double-pumper–style carbs
open the front set of throttle blades
before the secondaries to help
acceleration. But this will significantly
increase the air velocity through those
two barrels before the secondary set of
throttle blades opens up. Not good if
you are fighting booster tip.
By readjusting the throttle linkage,
you can cause the secondary blades to
open more quickly relative to the pri-
maries. This helps balance the airflow
throughout the carb so that one pair of
boosters doesn’t see too much air
velocity.HIGH-SPEED BLEEDS
Balancing the timing of the throttle
blades helped, but not enough.
Senior’s next step was to swap out the
adjustable high-speed air bleeds for
units with a smaller opening. The job
of the high-speed air bleeds is to pro-
vide air to emulsify the fuel before it is
injected into the airstream. By swap-
ping out to smaller air bleeds, the fuel
isn’t mixed with air as thoroughly, and
more fuel gets into the airstream. It
essentially provides a way to richen
the mixture without changing the
main jet size. The Ultra Dominator
came out of the box with size 32 high-
speed bleeds, and Senior swapped in
four that were size 30.Out of the box, the Ultra Dominator has a
power valve in the front metering block and
a blank in the rear—that’s the plug on the
right. We replaced it with a matching power
valve for the front (center). It helped, but
wasn’t quite enough, so Senior installed
two high-flow power valves (left). The high-
flow design is also known as a “four door”
because of the four flow slots versus the
standard power valve’s two.Prestige started with a 1,050-cfm 4150-sized Quick
Fuel carb, but found the engine wanted more air, so it
settled on a 1,250-cfm Ultra Dominator from Holley.
Thankfully, the Ultra Dominator is one of the most
tunable carburetors available today. That’s good,
because we needed it for this complex issue.