One of the features of a Hendrick Motorsports engine is that Hendrick has a wealth of resources in terms of engineers and equipment to continually improve performance. Also, like other NASCAR engines, those built by Hendrick have a large displacement capacity, which boosts horsepower.
The Hendrick engine team builds or rebuilds more than 700 engines a year. The engine department is responsible for designing and manufacturing components that will increase such things as horsepower and efficiency. The department runs a diagnostic on each engine after every race, keeping detailed records for reference.
In general, the cam profiles of engines used by NASCAR racers differ from those of standard vehicle engines. In NASCAR engines, air intake valves open at speeds at which valves would be closed on standard cars. That gives the engine a boost of air at high speeds. The engines also are tuned differently, optimizing the air and energy provided when the vehicle is traveling fast. Other high-powered engines could be tuned this way as well, but it would make the engine only function correctly at high speeds. The carburetors of race cars are tuned, for instance, to allow a large amount of fuel and air to enter the engine, which would not be useful at lower speeds.