frequently asked question

Why does the dyno show a power loss after a differential gear change (say a 3.42 to 4.10 gear)?

The Chassis Dynamometer measures power that reaches the tires, not Engine Power. Therefore, any changes you make to your drivetrain may result in a change in your chassis Dynamometer results. A steeper gear ratio will provide the following,

1. Higher peak force to the ground

2. Higher average force to the ground

3. Lower top speed (MPH)

4. Higher peak acceleration rate in all gears

5. Lower peak horsepower

The reason you lose your peak hp is based on higher acceleration rates, increased gear mesh/losses, higher tire losses. These will affect your peak horsepower number in a negative fashion. Losing approx. 5% is expected when changing to a significantly steeper rear gear. Engine power was not reduced, power to the ground was. In exchange, you have more force available which is what allows you to accelerate faster off the line. If you enjoy the feeling of Gs forces as you accelerate, you made a wise choice. Do not be discouraged by the peak power numbers—they are just a reference.