http://www.jayski.com/pages/diff.htm
Currently, the three top series — Nextel Cup, Busch and Craftsman Truck — run a 12:1 compression ratio. That rule went into effect during the 2001 season. They all use cast-iron, 5.7-liter V8 engines with aluminum cylinder heads, and each engine has a maximum displacement of 358 cubic inches.
But the main difference among the Cup, Busch and truck engines is the size of the carburetors — 830 cubic feet per minute (cfm) in Cup and 390 cfm for Busch and trucks — which allows a richer air-fuel mixture in Nextel Cup. According to the NASCAR media guide, the torque is 550 feet per pound at 7,500 RPM for Cup, 535 feet per pound at 6,500 RPM for Busch and 535 feet per pound at 6,500 RPM for trucks. That gives the engines the ability to produce horsepower in the range of 850 at 9,000 RPM for Cup, 750 at 8,400 RPM for Busch and 750 at 8,400 RPM for trucks.
Thank you! :-)
Speeds in both races seemed to be pretty close in my estimation.