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 affect on mixture distribution. If a carburetor's venturi is sized for low to midrange 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 midrange torque and throttle response will suffer. The correctly sized carburetor for some applications will be a compromise of low to midrange torque and top end horsepower.

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 midrange 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. Around the point that the intake tract is constricted, fuel is injected under pressure, allowing it to take maximum advantage of the air speed. In the converging tract manifold, most of the fuel that falls out of suspension as the wall is constricted is picked back up and put into suspension instead of being pushed along the walls.

"Fuel supplied into the nozzle of an EFI Hilborn injector can be as high as 60 pounds per square inch, allowing the injector to spray the fuel in a fan pattern. It also allows a consistently smaller-sized droplet, which is much more consistent than that of a booster. Therefore, the airspeed will not dictate the size of the droplet, which in turn allows the fuel to mix in better proportion with the air, providing improved engine efficiency and therefore making more power.

"Since a Hilborn injector does not require a bowl for fuel storage, it is an ideal system for any application that will create excessive fuel slosh as in road race and auto cross applications.

"Separation caused by the fuel crashing into the plenum floor is eliminated due to the individual throat design of the Hilborn injector. Also important is the reversion from one cylinder has no effect on the other cylinders. This allows each cylinder to act on its own, greatly improving the engine's ability to produce equal power from the fresh intake charge each cylinder receives on the intake stroke. Since each cylinder has its own throat, the line of sight to the intake valve is improved, resulting in a straighter shot for the air/fuel mixture. The fewer turns the mixture has to make, the more the fuel stays in suspension, providing enhanced distribution into each cylinder.

"The Hilborn injector has numerous advantages over carbureted systems. A carburetor requires a correctly sized venturi for its application in order to pull fuel out of the booster. However, the Hilborn, with its injected fuel, can maximize airflow potential by removing the restriction associated with the booster while enlarging the throat diameter allowing maximum breathing for the engine. This increase in throat size does not impede low-speed engine performance but enhances throttle response, and engine acceleration. This allows for maximum engine rpm output without sacrificing low-speed performance."

For maximum power, razor sharp throttle response, street-friendly driveability, and respectable fuel mileage it's quite apparent that the Hilborn fuel injector is the right choice and besides that, they look awesome -especially in a classic pickup!

Hilborn Fuel Injection
22892 Glenwood Drive
Aliso Viejo
CA  92656