Which carb spacer to use

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. But there's still the issue of total system volume versus engine airflow requirements, so in that sense spacers could still prove to be of benefit on EFI setups, although less so than in a traditional carbureted application.

Close Ad. Join MotorTrend. Eddie Otanez Via email. They may enhance fuel vaporization time by moving the boosters further away from the manifold runners. But they still have sharp edges on the bottom, which tends to separate the fuel out of the air, and may even cause reversion. Open spacer: Open spacers sometimes add a little more top-end power, but usually trade-off lower rpm performance to do so.

But as noted above a lot of this depends on the total combo, especially the camshaft. Aluminum, wood, and phenolic resin spacers can be stacked. Now that you know some of the basics concerning carburetor spacers, you should have a better idea of which type fits your needs.

Your email address will not be published. Your Website. Save my name, email, and website in this browser for the next time I comment. This site uses Akismet to reduce spam. Learn how your comment data is processed. Summit Racing Equipment. Underneath these twin Holley Dominators are two plywood carburetor spacers. During his year career in the auto industry, he has covered a variety of races, shows, and industry events and has authored articles for multiple magazines.

He has also partnered with mainstream and trade publications on a wide range of editorial projects. In , he helped establish OnAllCylinders, where he enjoys covering all facets of hot rodding and racing. What about runners on EFI cars such as Ford? You know, between upper and lower intake. Many single plane manifolds don't have any provisions for a manifold vacuum source for things like power brakes,a PCV valve, etc, so some guys will run a spacer that has a vacuum port on it when running a single plane manifold equipped street engine so they can run their power brakes or have a PCV line, etc.

What I do, rather than messing with the plenum size by using a spacer, is to just drill and tap the manifold before you install it , for a vacuum port. There are almost always places on manifolds to put one, either on the side of the plenum where we prefer to put them , or in one of the runners.

Now, do not confuse a carb "spacer" with a carb 'adapter'. Sometimes adapters are necessary when running a particular carburetor on a manifold that might not be designed for it, such as say, a spread bore Quadrajet carb on a square bore intake manifold, or vise versa.