This high-quality spun aluminum velocity stack is designed specifically to fit the 1.5 inch SU H4 / HS4 and Zenith-Stromberg CD150 carburetors on many Austin-Healey (100, 100-6, & 3000), Triumph Spitfire (Mk III, IV, & 1500), Triumph GT6, MG Midget 1500, and BMC Mini engines. (Please note that the vast majority of these vehicles have been modified over the past half century and may no longer have their original carburetors -- please be sure to check before ordering!)
This part is carefully crafted to the original Kas Kastner pattern. Dyno tests have shown an amazing increase of up to 4 horsepower on race-tuned four cylinder Triumph engines, and 6-8 horsepower increase on full-race Triumph GT-6s. The overall height including mounting flange is approximately 2.5" (+/- 0.25"), and the bell has a maximum OD of 5.2" (+/- 0.1"). Throat ID at mounting flange 1.375". Sold individually.
How does a 1 3/8" horn fit a 1 1/2" carb? Carburetor size nomenclature refers to the diameter of the throttle plate, not to the size of the inlet opening. H4/HS4 and CD150 carburetors have a 1.50" (38mm) diameter throttle butterfly. If you remove one of these carbs from the manifold, you will measure a 1.5" diameter outlet on the back of the carb. The opening on the inlet (air filter) side on all of these 1.5" carbs is 1.375" diameter.
