Size does matter. But, bigger isn’t necessarily better. Today we’re talking about carburetor spacers. Recently, I took a trip to High Velocity Heads (HVH) in Knoxville, Tennessee to learn more about their Super Sucker carb spacers. I asked owner Keith Petelle how a spacer works to increase horsepower and torque. He said, “It helps improve the air-fuel distribution into the intake manifold.”
Further research tells us that the air space between the carburetor and the intake manifold, called the plenum, can be a violent place. In a 604, for instance, the single plane manifold is deep and contains a centrally located plenum with runners that lead from the top of the manifold to the port entries in the cylinder head. The common plenum allows each cylinder to draw from all four of the carburetor venturis when the throttle is wide open. When the partially vaporized air-fuel mixture leaves the base of the carburetor, it forms four individual mixture streams. As the cylinders place a demand on the plenum chamber, the mixture streams physically bend in order to meet the demand. The runners within the manifold help to direct the stream and withdraw a larger volume of air-fuel mixture during the available induction time span. As each cylinder withdraws a charge from the plenum, the mixture streams constantly change direction. Adding to the chaos are pressure pulses that travel backward from the cylinders.
A carb spacer increases the distance between the intake manifold and the bottom of the carburetor, which reduces the velocity of the intake charge. A four-hole spacer helps to direct the air-fuel mixture, making the streams more efficient. It also assists in preventing reversion from the pressure pulses. Different configurations and sizes of spacers will affect the system differently, depending on a racer’s needs.
For short track racing, HVH sells both a 1/2" and a 5/8” spacer for 604 engines and a 1” spacer for the 602 engines. Most rules packages allow for a 1” spacer for the 604 and a 2” spacer for the 602. So, I asked Keith, “wouldn’t a bigger spacer be better?” He said, “Actually, the 604 likes a shorter spacer. The engine has a small cam and a larger intake manifold and head. Because the cam doesn’t match, the torque is reduced.” The correct spacer will increase throttle response and help the racer get off the corner faster.
You can find all of our HVH Carb Spacers in our online store. Click here to check them out.