Holley started using billet metering blocks a few years ago on the Ultra HP carburetors. The billet metering blocks are lightweight and are fully adjustable, with jets in all of the fuel circuits. The emulsion jets are replaceable, as are the power valve restrictions and the idle circuit jets. The replaceable power valve restrictions allow street guys to run leaner main jets for crisp freeway cruising, but still have plenty of fuel flow capability at wide open throttle.
The billet metering blocks are fully machined on all surfaces to provide better gasket sealing, and they have integrated pry points for easier disassembly. The metering blocks are black anodized for improved corrosion resistance, as well as good looks.
The fuel bowls are all new for these aluminum Ultra HP carbs. Not only are the fuel bowls lighter in weight, but they are slightly larger than previous fuel bowls. The extra size provides an additional 20-percent fuel capacity, but the longer length of the fuel bowl means that you might need to modify your fuel lines. The fuel inlet threads have also been changed, to a -8AN o-ring style inlet rather than the long standing 7/8-20 inverted flare fitting.
Holley started to use the clear Pyrex sight windows on some of the HP carburetors recently, but these new aluminum float bowls step up the game by putting sight widows on both sides of the bowl. Another handy feature on these new float bowls is the drain plug located on each bowl. The float bowls also have some internal baffles and troughs to reduce fuel slosh, minimize aeration, and route the fuel to the main jets.
The baseplates are machined from billet aluminum and then anodized. The mounting holes have been elongated so these carburetors will bolt on an intake with a Dominator flange, as well as any intake with a 4150 pattern. Even though the carburetor will physically bolt onto a Dominator flange, the linkage will not always clear the larger mounting flange used on 4500 style intakes. We ran into this problem when trying to install our 950 carburetor on a M1 intake, but the fix was fairly easy.
The throttle linkage has been simplified for racing by removing some of the passenger car brackets, and the idle screws have been fitted with knurled knobs for easier adjustment. The secondary linkage is adjustable and can be converted to 1:1 operation by simply selecting the alternate attachment point.
We were fortunate enough to get our new 950 carburetor onto our 514-inch engine that has been on the dyno multiple times. It usually makes about 825 horsepower with an 1150 Dominator carb, and we didn't want to change intake manifolds for this test, so we built a flat plate adapter to center the 4150 throttle bores over the large plenum in the Super Victor intake. The best power came on the third pull when we recorded 800 horsepower at 6,700 rpm. Swapping back to the 1150 Dominator produced a pull of 820 horsepower at 6,700 rpm, so we considered that to be a good A-B-A comparison test. It is possible that our flat plate adapter was costing us a little power when compared to a tapered adapter, so that is another variable that could be explored down the road.
The extra adjustability of Ultra HP design allowed us to quickly make the changes necessary. The idle-air bypass feature was handy for setting the idle speed without disturbing the relationship between the throttle blade and the transition slot, while the bowl drain feature makes jet changes a little faster and cleaner. All in all, we had great success with this new Holley design and look forward to using it on future projects.
The Cash Outlay
| Part | Part Number | Cost |
|---|
| Holley 950 | 80805BK | $749 |
| 9.75 inch fuel inlet | AT104195ERL | $90 |
This carb can be mounted to...
This carb can be mounted to either 4150 or 4500-style intake manifolds (notice the elongated mounting holes). This carb also has dual accelerator pumps, as well as four corner idle capabilities.
The aluminum Ultra HP carb...
The aluminum Ultra HP carb is longer than previous Holley 4150s, so a fuel inlet with a 9.75-inch center-to-center spacing is required. We used this -6 AN inlet assembly from Earl's.
A side by side comparison...
A side by side comparison with a Holley HP carb shows some obvious differences in the linkage as well as the castings. Not seen is the big difference in weight between these two carbs.
When we tried to bolt the...
When we tried to bolt the 950 carb onto this M1 4500-style intake, the throttle linkage hit the side of the carb pad. We happened to have a milling machine handy, but a little clearancing with a hand grinder can fix the problem.
The engine we used for testing...
The engine we used for testing was set up for a Dominator carb. We learned that while the carb will physically bolt to a 4500-style intake, some Dominator intakes have a really big plenum opening, and you'll end up with a vacuum leak along the sides of the carb. For dyno testing we built a simple adapter to mount the 4150 throttle bores to the 4500 spacer on our engine. We milled the back side of the spacer to provide a shear ring around each throttle bore.
The new 950 compared fairly...
The new 950 compared fairly well to the 1150 Dominator that we usually run on this 514-inch dyno motor. The 950 made excellent power right out of the box; all we did was adjusted the float level and then made full power dyno pulls. We did not need to change the jetting.