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Tuning With Carburetor Spacers

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Most people think of carburetor spacers as simple horsepower -  increasing devises.  In most cases carburetor spacers can be used to increase engine power levels, but even more important they can be used as sophisticated tuning aids.  Spacers often provide an increase in top-end power as well as mid range torque.  Typically, power gain comes from increased plenum volume.  To better understand spacers you must first learn of the different types, sizes, and thicknesses of carburetor spacers available. 

Carburetor Spacers come in 4 hole, open, and combination.  They are also available in different materials wood, plastic, and what is viewed to be the  most durable aluminum.  Carburetor spacers also come in several different thicknesses each providing a different effect. 

4 Hole Spacers 

A 4 hole spacer is one with 4 holes that align with the four barrels of the carburetor.  This spacer will increase throttle response and acceleration.  It can also lower torque and power-bands within the RPM range.  This is accomplished by keeping the columns of air and fuel flowing longer, which increases the air velocity.  Adding a 4 hole spacer can be an effective and practical solution for a vehicle with a sluggish throttle response or lethargic corner exit speeds.  In addition, a 4 hole spacer can also help compensate for an oversized component; such as, a carburetor, camshaft, or intake manifold.


Open Spacers

An open spacer is one with a large square - shaped hole beneath the carburetor.  This spacer will decrease throttle response and dampen acceleration.  It can also raise torque and power-band within the RPM range.  This is accomplished by increasing the plenum area.  Adding an open spacer can also be helpful in overcoming traction problems during acceleration or corner exit.  An open spacer can also compensate for an undersized component, such as a carburetor,camshaft or intake manifold.

Combination Spacers

A combination spacer is part 4 hole, and part open spacer.  A combination spacer can provide the best of both.  Choosing a combination spacer increases throttle response and acceleration.  A combination spacer can also increase or broaden the torque and power-band.  The four hole surface of the spacer interfaces with the base of the carburetor. 

Plenum Dividers             Coming soon!

In an open plenum intake manifold, a plenum divider partitions the plenum from side to side.  The divider helps prevent unwanted side to side fuel movement in high G-force oval track or road race applications.  On certain engines, it is common to have lean cylinders due to fuel surge.  An example would be a small-block Chevy oval track engine running on methanol can run lean on cylinders 3 and 5, while cylinders 4 and 6 are rich.  By using a plenum divider , equal fuel distribution can be restored to each cylinder bank. 

Spacer Thickness

A thicker spacer will increase the effect, that is , if a 1/2" thick spacer improves matters, a 2" thick spacer will further increase the effect.  Varying thicknesses of a spacer affects engine preformance. 

Spacer Materials

There are many different types of material used to make carburetor spacers.  Wood, plastic,and aluminum, are the most common.  Wood is a poor conductor of heat and not very efficient.  Plastic, or composite spacers are thermally efficient but are not as strong as phenolic (coming soon!) or aluminum. 

Spacers and Tuning

Since each carburetor spacer will react differently to each engine combination, there is neither a right nor a wrong type.  Spacer are valuable tuning aids.  They are especially  helpful when dialing in a new combination or when tuning a race car for varying race conditions.  Swapping out a spacer is a quick and simple procedure.  The change in spacers can have a significant influence on the drivability of a race car or street car. It is highly viewed by most, in the race car industry that  purchasing a carburetor spacer is a sound investment.