The increased fuel capacity...
The increased fuel capacity necessitated an increase in bowl size as you can see from this picture.
The shelf and its accompanying baffles has a secondary benefit. In the old design, under heavy acceleration the fuel runs to the back of the bowl and up that side and sloshes around, coming back up on top of the needle and float-this can cause problems with the needle and seat closing when you don't want them to. The shelf blocks this whole process from taking place. Instead in the new HP when the fuel comes back under heavy acceleration it hits the shelf and breaks apart instead of rolling all the way to the top like a wave on top of the float. The shelf in addition to all of the different baffles is designed to trap the fuel around the jets and prevent it from sloshing around. And it does so quite nicely.
In a circle track environment, you need to keep the fuel as close to the jets as possible. Conventional thinking says that when you're on a big track running high rpm over a long period of time, you begin to exhaust the fuel out of the bowl so if you lower the jets you will prevent fuel starvation. A common practice to achieve this is to mill out the floor of the bowl and then lower the jets farther into the fuel supply. However, this can cause leakage especially if it's done by somebody not familiar with carburetors. On the new HP, Holley beefed up the sealing lip of the floor so that if someone does decide to mill out the bottom to lower the jets themselves, there is still enough wall to have a solid seal. In addition, engineers created a trough to try and keep fuel on the jets as much as possible.
Here is another angle of the...
Here is another angle of the bowl comparison.
Typically when Holley puts the floats in it cores the section and uses self tapping screws. But that has changed. "We got enough feedback from users that they really prefer that we drill and tap those areas. That's one additional feature that we've added," says McFarland.
Holley is also offering the option to have either a plug or a pyrex sight glass on the new HP. This will allow racers to choose the option that best fits their needs and rules. Speaking of rules, one upgrade that caught our eye, small as it may be, is the fuel bowl drain. It is, for want of a better explanation a brake bleeder screw that allows you to drain fuel out of the bowls before disassembling the carburetor. We thought this was not only a great addition to tech officials who need to take fuel samples, but it's great for the racer too. Just answer this question:
How many times have you changed jets on the carb while it was still on the motor? We had to do that very swap during our recent Project G.R.E.E.N. test. It was dicey at best with the motor and headers hot from running laps on the track and time running short because of approaching bad weather. We got through it fine and none of the spilled fuel ignited but it sure would have been nice to have that fuel bowl drain on our carb. Hey, you can even put a vacuum pump on it a suck all the fuel out.
The metering blocks were designed...
The metering blocks were designed using CAD, in fact, Holley engineers designed the entire HP Aluminum Carb using CAD programs.
In addition to moving the machining of the billet metering blocks and billet baseplate in house, Holley has made a number of other improvements to the HP. The carb now features welded Teflon-coated shafts, with the primary shaft capped on the one end of the throttle shaft. This does a great job of keeping dust and dirt out of the shaft. The primary and secondary links are progressively adjustable so that you can adjust them without replacing links.
Holley has also developed a hand-adjustable speed (idle set) screw. "How many times have you been working on the car and you've tried to bump the speed up but you had to yell to a guy, 'Hey, go get a screwdriver,'" asks McFarland. "With this design you still can use a screwdriver but you have the option to use your fingers. We made it just big enough where you can get a grip on it and its got a nice chamfer on the end of it."