"The legendary Smokey Yunick states, 'The carburetor is a big restriction in the intake system. This is because in a round column of airflow, flow speed is fastest toward the center of the column. The design of the carburetor places the booster toward the center of that column in order to receive the strongest signal, or pressure drop at the booster, for maximum booster performance. Since airflow is impeded, the direction of part of that flow is diverted into eddies of spinning air that will disrupt the rest of the airflow around it.'
This is an example of an early...
This is an example of an early mechanical setup for the Ford Flathead V-8. These days Hilborn offers street-friendly electronic setups that are every bit as impressive to look at as they are dependable and streetable.
"Float bowl volume is essential for correct air/fuel ratio. With a needle and seat size a nominal .110-inch for gas, coupled with fuel pressure of 6 to 8 lbs psi at the needle and seat, it is difficult to keep the bowl filled. Carburetors use atmospheric pressure to provide lift of the fuel, therefore as the bowl empties, an increase in pressure drop is required to lift the fuel up the main well into the booster, compromising consistent air/fuel ratio. Fuel bowl problems also manifest themselves in applications that incur aggressive changes in direction, as in road-race and autocross applications.
"Cfm ratings for carburetors were introduced as a way to identify correct carburetor sizing for specific applications. In actuality, only the throttle blade size is needed to identify size, since a venturi will only flow so much air at a certain depression. Any published cfm ratings, regardless of product, should also include their depression in inches of water. Unlike the cylinder-head aftermarket where the standard for cfm ratings is 28 inches of mercury for pressure drop, there is nothing published for the carburetor aftermarket. As an example, all of Holley's 750-cfm carburetors use a 1.375 primary and secondary throttle blade, yet there are many companies who will claim up to 950 cfm with the same throttle blade size. These types of exaggerated specifications only lead to confusion for the end user on what size carburetor will fit his needs. Qualified carburetor shops will sell a carburetor by throttle blade size and not by exaggerated cfm ratings.
"At idle when air speed is low, the fuel droplet pulled from the booster is much larger than the one pulled when air speed is greatest or wide-open throttle. This has a profound effect on mixture distribution. If a carburetor's venturi is sized for low- to mid-range torque and strong acceleration, it will be too small to produce top-end power. Conversely, if the venturi is sized for top-end power, low- to mid-range torque and throttle response will suffer. The correctly sized carburetor for some applications will be a compromise of low- to mid-range torque and top-end horsepower."
With an abundance of ram tube...
With an abundance of ram tube and air filter designs, a Hilborn injection system can be tailored to the user's styling preferences-whether that's contemporary or traditional, they've got you covered.
The Eight-Stack Manifold"In a test conducted with a common plenum intake against the same engine with a Hilborn eight-stack manifold, with both adjusted to provide the same air/fuel ratio, the eight-stack manifold made more power. There are numerous reasons why.
"Without a carburetor's booster in the way, the eight-stack manifold will flow more air than a comparably sized carburetor venturi. Without the need for a pressure drop to supply fuel for the engine, the bore size of the eight-stack can be increased to supply the required air for top-end horsepower, yet have increased throttle response along with increased low- to mid-range power. The mild turning radius of the eight-stack intake helps promote line of sight for the air/fuel into the cylinder head. Since there is no common plentinum, the cylinders no longer need to digest an air/fuel mixture that is contaminated with pulses from companion cylinders. Since each cylinder is separate, there is no dilution to companion cylinders from reversion, eddy currents, fuel puddles, and the tight bends for the air/fuel to follow causing mixture distribution concerns.
"The eight-stack manifold employs a converging tract design, meaning the larger ram tube top is reduced in size as it enters the lower portion of the manifold before entering the opening of the cylinder head runner. With this design, air/fuel speed is increased when going from the larger opening to the smaller opening, ensuring that the air/fuel stays in suspension, unlike the tract of the common plenum manifold, which allows the air to slow when going from the small venturi of the carburetor to the larger opening of the plenum.