Picking the Perfect Spacer

carburetor, racing, spacers, throttle body -

Picking the Perfect Spacer

Whether you’re carbureted or fuel-injected, improving the efficiency of your combination is key to making power and winning races. If you have room under your hood, adding a spacer can help you pick up horsepower, improve part-throttle driveability and acceleration, improve distribution, increase plenum volume, clear some space for your linkage setup, or all of the above!

Picking the correct carburetor/throttle body spacer can be a daunting task with all of the options available on the market these days, but we’re here to help! There are a few crucial questions that will help to narrow down which spacer you should be looking at:

  1. What is this spacer going under (Carburetor? Throttle body? EFI Elbow?)
  2. What manifold is the spacer being used with?
  3. What type of application is it for? (Street, Drag Race, Offshore Boats, Dirt Late Model, Road Race, Offroad truck, etc)

4150 vs 4500: An easy way to differentiate which spacer you need is to determine if you have a 4150 or 4500 style manifold and carburetor/throttle body. 

Choosing The Perfect Spacer - Wilson Manifolds Blog


We make our spacers for both 4150 and 4500 (Dominator) patterns. 

The vast majority of 4150 carburetors and throttle bodies utilize 1.750” throttle bores, so our 4150 4-hole spacer is designed with 1.750” bores to match.

When it comes to 4500 (Dominator) carburetors and throttle bodies, there’s a bit more to it. We make many different 4500 4-hole spacers so that you can match our spacer to the bore size of your carburetor or throttle body. You’ll want to select a spacer with either the same bore size as your carburetor/throttle body or slightly larger. You would not want to pick a spacer with a smaller bore size than your carburetor/throttle body as that will cause a disturbance in the air flow.

4-Hole Tapered vs Open: The next way to differentiate our spacers is by open or 4-hole tapered. 4-Hole tapered spacers are the go-to unless the spacer is going under an elbow. Open spacers only improve plenum volume, but won’t pick up the CFM of the carburetor or throttle body the way the 4-hole tapered spacer does. Wilson Manifolds 4-Hole Tapered Spacers feature a computer generated variable radius taper design that maximizes the airflow through the carburetor and enhances air/fuel distribution for more horsepower.

CFM is picked up using our proprietary convergence design inspired by cutting-edge fluid dynamics technology. This design ensures the mixture entering the plenum has the least amount of air/fuel separation possible, which results in improved horsepower, torque, acceleration, and fuel mileage.

This design originated here at Wilson Manifolds in the 1980s and has been perfected over decades of research and development on the street, at the racetrack, on the water, and on the dyno.


Many variables are at play when determining how tall of a spacer to use for a specific application, such as camshaft specs, manifold size, cylinder head specs, hood height, etc. Some engine combinations benefit most from a tall spacer while others will perform better with a short spacer.

Generally, we recommend 1” tall spacers for street-driven applications. A spacer with 1” height will pick up power and improve distribution throughout the powerband without any compromises. 

For maximum power on dedicated racing applications, you want the tallest spacer possible as long as the engine accepts the added volume -- often this will be a 2” tall spacer. These taller spacers will pick up power on the big end of the powerband, though you may sacrifice some low-end grunt. If the engine spends most or all of its life in the upper regions of the powerband, these tall spacers are the way to go.

For example, here are the flow numbers in CFM for our 4500 2.00” bore throttle body:

  • Throttle Body Only:   1745cfm
  • w/ 1" tapered spacer:    1875cfm
  • w/ 1.5" tapered spacer: 1880cfm
  • w/ 2" tapered spacer:    1890cfm

By adding a spacer under our throttle body, CFM is improved substantially. 

If you have any further questions about which spacer is right for your project, feel free to give us a call (954-771-6216) or send us an email to info@wilsonmanifolds.com. We’re always happy to help!