For all racing applications, our  V-Max Variable Duration Lifters are the answer. They increase low-end torque and engine vacuum up to 50% more than Original Rhoads Lifters...and they rev higher too. This makes them the best choice for all racing applications. Typical vacuum increases range between 2 to 4 inches at idle when used with bigger cams. They are fully adjustable and require an adjustable valve train. Adjustment is similar to solid lifters. Simply use a feeler gauge to adjust the exact amount of lift reduction you want, anywhere from .010" to .040", and that is exactly what you get at idle. Duration is reduced between 5 and 20 degrees at .050" lift depending on the adjustment. As the rpm increases, so does the lift and duration. Full restoration takes place at approximately 4000 rpm. They may also be used with solid lifter cam in racing applications only.  They are particularly suited for racing applications with vacuum rules. You can run a bigger cam than your competition while still meeting vacuum requirements, giving you the performance advantage.  Our Super Lube Groove Option is highly recommended for better lubrication and longer cam and lifter life.