Car Craft – November 2019

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36 CAR CRAFT NOVEMBER 2019

The main-channel air bleeds were dropped

from 28s to 25s.

In high-end carbs like the Ultra Dominator,

there are flow restrictors that limit fuel flow

once the power valve is open. We simply

removed them to richen the mixture.

MORE POWER VALVE

A carburetor’s power valve is initiated

by vacuum conditions to allow

additional fuel into the airstream when

necessary. The idea is that when you

apply throttle, the blades in the

carburetor open, dropping vacuum in

the engine. The power valve sees this

drop in vacuum and provides needed

fuel for acceleration until the air speed

through the carburetor picks up and

the main jets can, once again, provide

the necessary fuel. It is similar to the

accelerator pump, but doesn’t depend

on throttle-pedal position.

The Dominator comes stock with

only a power valve in the front billet

metering block. The secondary side is

machined to accept a power valve, but

is plugged. Senior began by swapping

out the plug for a second power valve.

That helped, but more fuel was still

needed. So next we took the restrictors

out of the power-valve circuits. This

option isn’t too commonly available in

many carburetors, but it is one of the

many adjustment options on the Ultra

series of carbs from Holley.

Again, that helped, but even more

fuel was needed, so the next step was

to remove both power valves and drop

in a pair of high-flow power valves. The

stock power valve was rated at 5.5, so

we kept that same rating for the new

high-flow power valves.

MAIN-CHANNEL

AIR BLEEDS

The final change was to swap out the

main-channel air bleeds for a smaller

size. Again, the idea—just as with the

high-speed air bleeds—is to reduce the

airflow so there’s less emulsification of

the fuel, which will richen the mixture.

The Ultra Dominator has adjustable

main-channel air bleeds in the billet

metering blocks, and we changed out

the stock 28-sized restrictors to 25s.

On the engine dyno, we finally saw

a fuel curve that made Senior happy.

Previously, to get enough fuel into the

engine at WOT, Senior had upped the jet

sizes from 92 in the front to 102 and

102 in the rear to 105. With these

changes, we were able to bring the jets

back down to 96 and 100 front and rear

while maintaining a proper fuel curve

throughout the rpm range. Success!

THE NEXT STEP

A common trait we’ve noticed among

the very best engine builders is never

being able to leave well enough alone.

Now that the big Ultra Dominator carb

was functioning properly, Senior pulled

it off the engine and bolted up one of

Holley’s new Dominator-sized Sniper

Stealth 4500 fuel injection systems for

a little A/B testing. This is the Sniper

system for big-inch engines with a

1,440-cfm rating, eight 100-lb/hr

injectors, and integrated timing

controls. We did, however, keep the

DUI HEI distributor in place instead of

accessing the built-in timing controls

to limit variables for this test. Holley

says this system is capable of handling

1,500 hp naturally aspirated or 1,250

hp with forced induction. Maybe most

ON THE DYNO

ULTRA DOMINATOR VS. SNIPER STEALTH

RPM

CARB EFI

TQ HP A/F TQ HP A/F

2,500 682.2 324.7 12.17 642.6 305.9 12.71

2,600 693.5 343.3 12.15 656.1 324.8 12.62

2,700 712.5 366.3 12.24 678.2 348.7 12.64

2,800 728.7 388.5 12.33 685.8 365.6 12.61

2,900 745.4 411.6 12.34 690.7 381.4 12.42

3,000 760.3 434.3 12.27 704.2 402.2 12.08

3,100 771.9 455.6 12.30 726.3 428.7 11.70

3,200 776.2 472.9 12.41 744.4 453.6 11.43

3,300 770.5 484.1 12.27 752.8 473.0 11.46

3,400 762.3 493.5 12.27 753.2 487.6 11.66

3,500 756.6 504.2 12.37 748.5 498.8 11.93

3,600 754.3 517.0 12.54 744.3 510.2 12.34

3,700 762.4 537.1 12.66 742.3 522.9 12.47

3,800 785.5 568.3 12.77 747.5 540.8 12.49

3,900 800.8 594.7 12.78 764.6 567.8 12.66

4,000 806.8 614.5 12.67 785.4 598.2 12.95

4,100 813.5 635.1 12.61 792.7 618.8 12.78

4,200 818.3 654.4 12.57 818.7 654.7 12.27

4,300 821.8 672.8 12.61 820.1 671.4 11.92

4,400 824.4 690.7 12.69 825.5 691.6 11.87

4,500 824.9 706.8 12.71 827.3 708.8 11.86

4,600 818.4 716.8 12.69 824.5 722.1 11.89

4,700 810.6 725.4 12.71 817.5 731.6 12.03

4,800 803.3 734.2 12.62 811.2 741.4 12.07

4,900 794.1 740.9 12.54 802.0 748.2 12.06

5,000 786.9 749.1 12.60 793.7 755.6 12.11

5,100 784.6 761.9 12.69 790.0 767.1 12.10

5,200 779.2 771.5 12.80 786.9 779.1 12.13

5,300 771.2 778.2 12.75 777.7 784.8 12.11

5,400 760.9 782.3 12.72 765.3 786.9 12.19

5,500 745.2 780.4 12.71 751.2 786.7 12.35

5,600 733.2 781.8 12.64 738.5 787.4 12.40