This video answers the question of how much you can tune a naturally aspirated vehicle by using a dyno as a tool for checking tweaks to both the air-fuel ratio and ignition timing. The guinea pig for this test is a stock 2000 Dodge Viper with just 38,000 miles (61,155 kilometers).
The first step is to get a baseline output on the dyno and check the air-fuel ratio through the rev range. The factory rates this 8.0-liter V10 at 450 horsepower (336 kilowatts) and 490 pound-feet of torque (664 Newton-meters) of torque at the crank. This one is putting down 410 hp (306 kW) and 450 lb-ft (610 Nm) at the wheels. This works out to a drivetrain loss of 8.89 percent, which is impressive for a 20-year-old car.
Gallery: Second-Generation Dodge Viper (1996-2002)
The initial run shows the Viper running rich in the middle of the rev range, so the tuner reduces the air-fuel ratio. Another test on the dyno now shows the Viper making 412 hp (307 kW) and 457 lb-ft (620 Nm).
From there, the tuner continues to tweak the air-fuel ratio until things are ideal. Then, he starts advancing the ignition timing. At this point, the dyno shows the engine making 435 hp (324 kW) and 475 lb-ft (644 Nm). However, adjusting the timing causes the mill to run lean, so the air-fuel ratio needs further changes.
After making the final adjustments, the dyno shows the engine making 438 hp (327 kW) and 483 lb-ft (655 Nm) at the wheels (see the graph above). Compared to the first run, the powerplant now has 6.8 percent more horsepower and 7.3 percent more torque than the stock setup. The tuner believes this is as far as possible to go safely while running on pump gas, at least without installing aftermarket components.
In the real world, the result of this change is that acceleration from 30 mph to 80 mph in second gear goes from 5.93 seconds in stock form to 5.53 seconds with the engine parameter tweaks.