This combination yielded the largest and highest torque curve, which peaked at 663.4 lb-ft at 3,700 rpm. The engine delivered 19 inches of manifold vacuum at 800 rpm with the total ignition timing set at 33 degrees. But what's especially amazing is at just 2,000 rpm, the 572 now had 595 lb-ft of torque. Granted, our peak horsepower numbers dropped from 648 to 549, but torque is what accelerates a car. We performed all of our testing with 91-octane Chevron.