Specially designed for drag race applications to isolate carburetor from manifold spacers prevent horsepower-robbing heat transfer and increase the distance from the bottom of the carburetor to the manifold plenum for better air flow Spacers are CNC-machined in the U S from a polymer compound able to withstand temperatures up to 400°F Available in open or four hole versions for 4150 and 4500 series Holley and Holley style carburetors in 1/2" 1" and 2" thicknesses Tapered four-hole spacers have specially contoured holes to increase air velocity under the carburetor Not intended or recommended for street or circle track use