390 gears

The 8-1/4 is strong enough to handle 400 hp but a c-clip eliminator kit is really good to have. How a car drives with a particular gear is dependent on the tire size. If you have 28" tall tires with 3.90 gears it'll spin about 3100 at 60 mph. If you have 3.90 gears with 24-25" tall tires it'll spin a whole bunch more rpm.