Carburetor Spacers

Common consensus asserts that a carburetor spacer is a simple engine-tuning device, useable for only a select few applications, and they don’t produce much extra power either. Sweet and simple, however that might not be completely true. Certainly in many cases they can be used to change engine characteristics. But they can also be used to find measurable horsepower (more on that later). Here are the bare bones basics of how a spacer functions:

What a Spacer Does
The addition of a spacer effectively increases the distance between the carburetor and the floor of the intake manifold plenum. In many cases, this straightens out the intake mixture flow pattern. Because of this added distance, the carburetor signal is weakened. And when the signal is weakened then larger jets in the carburetor will be required. Carburetor spacers designed with four separate holes tend to recapture the velocity of the mixture stream, which has been lost when an open carburetor spacer is installed. In simple terms, more exit velocity in the mixture stream creates a stronger carburetor signal than that found with an open spacer. Generally speaking, the jet size will still have to be increased when a four-hole spacer is used, but not as much as with an open spacer.


How much spacer should you use? As a rule of thumb, single plane intake manifolds seem to respond best with larger spacers (in the order of 2-inches in height and larger). On the other hand, most dual plane intake manifolds work best with open spacers with a height of between 5/8-inch and 1-1/2-inches.

Material World
When it comes to materials for spacers, plywood is a pretty good choice. Thin layers of laminated wood, bonded together with resin, form a natural heat sink. For example, a wooden spacer features top quality hardwood plywood with a sheet of phenolic resin-impregnated paper bonded to both sides. As expected, plywood spacers are easy to modify to suit a given manifold for optimum performance. On the other hand, pure phenolic spacers are constructed from an advanced composite material (similar to plastic), which can reduce heat conductivity 10 times greater than aluminum for a much denser air/fuel charge. Obviously, aluminum spacers are still widely available. The advantage in aluminum is that it can be easily modified for a given application. The disadvantage is that in some cases, an aluminum casting can be porous. Because of this, several manufacturers now offer billet aluminum spacers CNC-machined from 6061-T6 material.

So Do They Work?
For the most part, the answer is yes. Certain engine combinations respond more favorably than others, particularly to traditional spacers. But there’s a new wrinkle in the world of carb spacers and airflow. It’s called a “Super Sucker,” and it’s manufactured by a company named “HVH” (High Velocity Heads). Like others, it’s made from an advanced composite material. And like others, most are 1-inch tall. And yes, the topside (carburetor mount side) looks like any other four-hole spacer. But the bottom (intake manifold side) is far different than anything seen before (see the accompanying photos). Ok. It’s different, but does it work? We tested one with remarkable results: