Doug Thorley Headers THY-303Y-DA-C long tube tri-y headers deliver the ultimate in performance and gas mileage for your 1973-1991 GM Pickup Truck , Suburban, Blazer/Jimmy, 2WD ONLY and 1975-2001 Class 'A' Motorhome with the P-30 chassis. Doug Thorley Headers is the originator of the tri-y header design, which is the most efficient way to increase horsepower and torque over a broad RPM range, and more importantly the range where you use it most. The headers are manufactured using heavy duty 14GA steel tubing, and super flat 3/8 inch head flanges. They are then silver ceramic coated inside and out, which looks great, drastically reduces under-hood temperatures, and creates a strong barrier to protect the headers from the environment. APPLICATION SPECIFICS: 1973-1991 GM Pickup Truck , Suburban, full-size Blazer, full-size Jimmy / 1975-2001 Class A Motorhome, P-30 chassis, 366-454 V8, 2WD ONLY, will not fit D-port cylinder heads, with 8 air injection fittings (7/8 inch). No y-pipes included, may require professional installation.