By JEFF SMITH MARCH 28, 2023
Our friends at Westech performed a major dyno test a number of years ago that tested a whole series of single-plane small-block Chevy intake manifolds. One major detail that jumped out at us after all the data was assembled was that power for both average and peak horsepower was directly related to carburetor mounting pad height. This was measured between the rear carb mounting pad and the rear china wall point of the manifold. This sounds overly simplistic, but the data did not lie. We’ve pulled details from three Edelbrock small-block manifolds to illustrate this point.
The test engine was a 400ci small-block Chevy making nearly 550 horsepower. We assembled a chart that lists average and peak horsepower as well as the carburetor mounting height. By studying the chart, it’s clear that carb height plays an important role in both average torque and peak horsepower. The chart also indicates the power difference between the short Torker II and the taller manifolds. A 57-horsepower increase is certainly worthy of notice!
Another important point worth mentioning is that manifold port design plays a significant role in this trend. In other words, just bolting a 1-inch-tall spacer on a Torker II manifold will not improve power by 50 horsepower. But, it will help both average and peak power. The idea behind this is that by increasing the distance between the throttle plates on the carburetor to the plenum floor, it allows the air and fuel to more gradually transition into the intake ports and reduce turbulence. Another variable that can help with this transition is a larger CFM carburetor, because the larger venturi will slow air and fuel speed exiting the carburetor and allow the mass flow to more easily make the transition.
If increasing average torque along with peak horsepower is one of your goals and there’s room to fit a taller carbureted intake manifold under the hood, it’s worth the effort. As an aside, this same concept of a taller carb mounting height applies to dual-plane manifolds as well. It’s a simple idea – but it works!
The critical depth is the distance from the carb mounting flange to the manifold floor. As this depth increases, it offers more of a gradual turn for the air and fuel leaving the carburetor to enter the intake ports. A short height makes this transition much too abrupt which causes turbulence in the manifold and directly affects power.
