HotRod Dec. 2014 Issue
















RCS Performance Engineering

Fuel Systems

From the picture above is an Electronic Fuel Injected IR (Individual Runner) fuel system, which has 8 individual throttle bodies. IR fuel systems are commonly used in road racing applications where hood clearances require a lower profile induction. There are no advantages to using an IR over a single 4 barrel manifold, actually the power bands can be rather short in width and the power levels are still not as good as a EFI 4 barrel conversion manifold, while induction reversion seems to be a large part of its demise. Nostalgia in design they look really cool and offer a challenge to novice tuners, requiring a manometer to set each throttle blade angle/air gaps to balance the throttle blades for idle quality and drivability.

4150 Series Holley Carburetors

Holley carburetors as a fuel system can be a great choice for reliability and cost, old school performance that may never go away. 4150 style carburetors are universal, and have a wide range of adjustable, although there are several other models than the ones below the 4150 Series. Carburetor tuning is fairly basic and easy for the novice if they have an understanding of the engines demands, the only issue would be to know what the engine requires before you go at it. You have basically 5 fuel circuits that deliver fuel to the engine. During operation you may only require as few as 1 to 2 while the remaining 3 others begin to work as the throttle is opened. Some tunnel ram carburetors may have a 6th circuit to aid in tuning part throttle transitions. Every carburetor has air bleeds to add air to the metered fuel to aid in fuel atomization and fuel emulsion. At his level of tuning it is not necessary to modify the air bleeds.

Below are a pair of 4150 Series 750 cfm Carburetors

2x4 Carburetion

Below are a pair of 4500 Series 1150 cfm Dominator Carburetors

2x4 Dominators

EFI Converted 4 barrel manifolds are a great choice when retro-fitting an EFI fuel system to a center throttle body manifold. Single 4 barrel manifolds appear to be the perfect intake manifolds being actually centered on the engine, but they suffer extreme amounts of pulsation at low air speed due to runner length variation and sizes.

Don't let me scare you, they're a great choice in creating a strong wide power band that can support high rpm power. Small plenums help in creating a path to the runners supporting a combine effort for filling all the ports and can boost volumetric efficiency simulating the effect of longer intake runners. The placement of the injectors has some versatility and creates an open area to work with.

EFI Converted 4 Barrel Manifolds

In the upper picture is a 1,325 CFM 4 barrel (butterfly) throttle body using a 4150 bolt pattern, while below is a 2,400 CFM 4 barrel (butterfly) throttle body using a 4150-4500 dual bolt pattern.

2400 CFM Throttle Body

EFI Supercharged EFI fuel systems are another choice. The fuel injectors are just above the blower housing and below the throttle hat. Not like in a 4 barrel manifold where they are halfway down the runners. This can create an issue with fuel spray (a fine mist) exiting the throttle blades under low engines speeds or even possibly higher speeds until boost builds. This comes from having a limiting or restricted exhaust system with a blower, and or when using in conjunction a larger camshaft duration with increased overlap. Induction air speed is generally slow at this point due to the large opening above the blower impellors, reversion plays a rule allowing fuel to be thrown around by the impellors. Other than that when it comes to fuel delivery it’s nothing more than having two carburetors above the blower. Where the benefit comes is the fuel is sprayed into the blower impellors and with carburetors the fuel has to be drawn in through the booster. When it comes to performance, spraying the fuel into the engines increase the throttle response tremendously over a carbureted fuel system. The mass weight of the fuel slows down the available air and fuel when using a carburetor hence slower acceleration, this unfortunate issue is applicable to all carbureted applications not just a supercharger.

EFI Blower Hat

In the next EFI manifold the throttle is in front of engine creating a larger plemum for air to be stored, complimenting the longer intake runners that support cylinder fill. The injectors are placed low in the intake runner so fuel standoff exiting the throttle body is not present.

EFI throttle body