Just some info I thought I would put out for you guys and gal. A car having 3:27 rear end gears is placed on a DynoJet chassis dyno and has a dyno performed. Then this same car is taken off the DynoJet chassis dyno and has the rear end gears changed to 4:10. The car is then placed back on the DynoJet chassis dyno and another dyno is performed. Will the second dyno show a loss of horse power caused by the 3:27 to 4:10 gear change? ANSWER: Yes. This has been a long standing debate among car enthusiast, so I recently emailed DynoJet and asked this exact question. Below is the response I received. "The 4:10 gear will show less horsepower than the 3:27. The reason is due to rate of acceleration changes. The rate of acceleration is quicker with the 4:10 because of torque multiplication being increased to the rear wheel. The horsepower will show less because the targeted RPM is met before the horsepower has a chance to overcome the rotational mass (dyno, drive line, etc.) or moment of inertia in speed. Because the speed is decreased and the RPM is met faster, the horsepower never has a chance to catch up with itself, so to speak. The overall ratio of 1:1 will always produce the most horsepower on the chassis dyno. Having said this, a similar problem can occur with horsepower loss when the rear gear is too high. The horsepower is being absorbed in just trying to keep the rotational mass spinning. Please keep in mind that your engine's horsepower never changes but what gets to the dyno or drive surface does.