Chevy Carburetor Build - Custom Small-Block Chevy Carb

We can just see some of the younger generation out there grinning at their older counterparts and asking, "What's a carburetor?" The mature generation turns red in the face, makes a fist and replies, "I got your carburetor right here!"

Not that we're trying to provoke anything, but the carburetion versus fuel-injection battle will last forever-at least until we start levitating from earth in our hovercraft. With apologies to the fuel-injection crowd, this story is all about carburetion and how it is modified for blow-through supercharged applications.

The technicians at The Carb Shop make this look easy, building a stout high-hp blow-through carburetor like they do here. Our technician, O.J. Bretzing, starts out with a basic Holley 950 HP carb and builds it up from there. First the butterflies are removed from the carb baseplate in order to gain access to the throttle shafts. New seals that can handle 30 psi of boost need to go into the shafts.

The technicians at The Carb Shop make this look easy, building a stout high-hp blow-throug

As a younger version of Dan Ryder, carefree and flying solo in the companion department-as opposed to the weight-gaining/gray-haired/married version-horsepower was atop the list of things to obsess about. With superchargers gaining in popularity, I wanted to be one of the few with a carbureted blow-through system. After mustering up enough dough and bolting the system to my 11:1 compression small-block, reality quickly set in. At first the car started right up, but bogged on acceleration. After making a few calls for help, it was brought to my attention that I hadn't removed the choke horn from the Holley 650 atop the intake. This resulted in airflow obstruction between the carburetor hat and the choke horn.

Beyond removal of the horn via a dremel tool and cut-off wheel, the car ran phenomenally-for about 30 seconds. Suddenly, antifreeze was puking from the exhaust. That's right: Pump gas, 11:1 compression and 10-psi of boost didn't work out too well. Detonation occurred, resulting in exploded cylinder head gaskets! I guess I can be called a "self-learner," which came at substantial cost. Beyond the frustration, it was mission abort on the blow-through system.

Before the new seals are installed, further machining of the baseplate is performed to meet The Carb Shop's exacting standards for functionality and fitment.

Before the new seals are installed, further machining of the baseplate is performed to mee

Some 15 or so years later, dj vu is setting in. This time, however, I've got the patience to perform additional research, as well as consulting professionals in the field for some assistance. Since we are utilizing a ProCharger F2 on Project True SStreet (our '87 Monte Carlo SS), I decided to check out ProCharger's Web site for some insight (www.procharger.com). The site contained an online newsletter entitled "Blow-through Carb Considerations."

After a brief read-through, the relationship needed between the blow-through setup and the carburetor became clearer. Valuable information was gained, such as the fact that modifications would include the use of annular discharge boosters, power-valve restriction modifications, accelerator-pump pullover enrichment, air-bleed sizing, larger needle and seat assemblies, along with a plethora of custom tricks to provide a flat fuel curve under boost and driveability, sans boost.

The new heavy-duty, boost-friendly seals are secured with red Loctite.

Additional modifications are to include nitrophyl floats-because the brass units may collapse under boost pressure-the use of a boost-referenced fuel pressure regulator, and a fuel pump with enough volume to keep the fuel bowls filled under wide-open throttle conditions.

Since True SStreet will be seeing extremely high levels of boost and pumping out over 1,000 hp, we decided to leave the carburetor modifications to the professionals at The Carb Shop in Ontario, California. The Carb Shop houses its own in-house engine dyno for real-world testing and adjustments, as well as utilizing its own custom components for proper modification. We called upon Holley for the 950 HP main body that will be used as the starting foundation (as per The Carb Shop's instruction). The Carb Shop has built many custom blow-through units for enthusiasts across the country and was eager to help us out.

Not a chance of them leaking or moving now.
The throttle shaft is now too large to fit with the new seals. Measuring in at .368, the shaft is machined down to .350.
The throttle shaft is now too large to fit with the new seals. Measuring in at .368, the s
If this was not performed, the seal would rotate within the shaft rather than seal on the actual shaft arm.
If this was not performed, the seal would rotate within the shaft rather than seal on the

Now that all machine work has been completed, the newly revamped baseplate is reassembled.
It is interesting to note that there is a new throttle linkage hole for two possible throttle positions. The first hole positions the throttle for a more street-friendly application, while the second is more aggressive. When the primaries are open at around 15-20 percent in the more aggressive position, the secondaries also start opening.
It is interesting to note that there is a new throttle linkage hole for two possible throt
On the main body of the carburetor, The Carb Shop uses specially made high-flow boosters that will move larger amounts of fuel, which is required to feed the need of a blower mill.
On the main body of the carburetor, The Carb Shop uses specially made high-flow boosters t

In this photo, O.J. is wedging in the new boosters.
To make sure everything seals perfectly, all gasket-sealing surfaces on the main body are milled down. A leaky gasket can wreak havoc, causing a loss in boost pressure.
To make sure everything seals perfectly, all gasket-sealing surfaces on the main body are
After the milling process is completed, O.J. chamfers or rolls all entry points to remove any possible burrs that may exist.
After the milling process is completed, O.J. chamfers or rolls all entry points to remove

Once the larger vent tubes are added to the main body (for better ventilation of the fuel bowls), it is complete.
Once the larger vent tubes are added to the main body (for better ventilation of the fuel
Both the primary and secondary metering blocks start out as blanks and are worked over like one of Rocky Balboa's punching bags.
Both the primary and secondary metering blocks start out as blanks and are worked over lik
The metering blocks are worked to ensure that the fuel curve is linear and moving the correct amounts of fuel.
The metering blocks are worked to ensure that the fuel curve is linear and moving the corr

In this photo the accelerator pump passages are plugged. That is standard procedure on the blank metering blocks.
In this photo the accelerator pump passages are plugged. That is standard procedure on the
Once completed, the metering blocks are set to the side for the moment.
Fresh from the machine shop is a set of exclusively made billet dual needle and seat bowls. After they are sonic washed, they are ready for assembly. These bowls are the latest addition to The Carb Shop's inventory of performance parts. These are specially made to increase the fuel amount in the bowl. In high-fuel demand situations you can't move enough fuel through one needle and seat.
Fresh from the machine shop is a set of exclusively made billet dual needle and seat bowls

There are sight plugs on both sides of the bowls installed. Now it is easy enough to see the float level on either side of the bowl.
There are sight plugs on both sides of the bowls installed. Now it is easy enough to see t
Both bowls receive a set of monster-sized 50cc accelerator pumps.
O.J. sets the floats to a baseline level prior to final dyno tuning of the carburetor.

Now that all parts have been machined and built...
...they all come together for final assembly.
With every panel properly installed and square, final welding begins. External seams at the bottom of the rear windshield are welded smooth.
With every panel properly installed and square, final welding begins. External seams at th