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.
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.
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.
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.