Spacers isolate carburetor from manifold, preventing horsepower-robbing heat transfer while also increasing air flow due to the increase in distance from the bottom of the carburetor to the manifold plenum Spacers are precision cNc-machined in the US from a state-of-the-art polymer compound and can withstand temperatures up to 400deg F Available in open or four hole versions for popular 4150 and 4500 Holley style carburetors in 12 inch, 1 inch and 2 inch thicknesses Four hole spacers are additionally offered with specially contoured holes which helps increase air velocity under the carburetor For Drag Race Only