Building A Blow-Through Carburetor - Feeding The Fire

Another modification is to change the size of the main well where the fuel is emulsified. This allows the carb to move the amount of fuel it needs. Think about it, these carbs were never designed to support 2,000 hp.

At this time, the booster exit on the metering block is plunge-cut for a smoother transition.

To reassemble the carb, new air bleeds were installed, featuring a different orifice size that are calibrated specifically for our engine combination.

Idle mixture screws were put back into the metering block. To set them, they're first turned all the way in and then backed out by a turn and a half as a starting point.

Next, the four power valve restrictors were enlarged to a proprietary size, one for each main jet.

From here the boost-activated power valves were installed. Unlike standard power valves, which work off of vacuum, the new power valves are boost activated, allowing a more linear fuel curve as the boost comes in.

The needle and seat used is different in where the fuel exits. The standard design has the fuel coming out of the window just below the seat (right), where as the down-feed design (left) exits the fuel as it sounds-from the bottom. The needle then rides on the float and helps minimize aeration.

To provide maximum fuel under hard acceleration, The Carb Shop utilizes a press-fit power valve extension that gets its fuel from the back of the bowl, similar to jet extensions. Below that are the two jet extensions. The horsepower level and engine combination determine which jets are placed into the metering blocks; in this case, 84/89 jets were installed as a starting point for its new home-a 540ci big-block.

The billet aluminum float bowls shown here are unique in that they feature AN-6 fittings, dual needles and seats with dual floats, and significantly larger fuel bowls to prevent starvation.

As a comparison, here's the latest design that The Carb Shop will be converting over to. Mechanically, the newer design works the same; the change is simply for a smoother modern look.

With both bowls installed, the upper AN fittings and braided-stainless line are put in place. This is the balance tube, which helps to equalize the float bowl pressure.

Before leaving the shop, every carburetor is tested with the in-house mule, a 532ci big-block with a ProCharger F2 huffer. Old reliable here has been proven to hit 1,100hp figures with ease. They also have a 535ci big-block with a set of Brodix heads that generates 1,660 hp around 7,500 rpm. Boost levels are around 16 to 17 psi for the 532ci, whereas the 535ci peaks in around 18 psi.