Chevy Chevelle Rear Axle Power Charts - The Great Rear Axle Comparo

This may be due to the power required to spin the larger ring gear, but that doesn't account for the fact that it appears the curve is beginning to climb at the last data point. Send us your theory on that one. What is apparent is how much the 9-inch power curve drops off at the higher engine speeds. If we had used an engine with more rpm potential, the power difference may have been even greater at 7,000 rpm. The horsepower difference at 5,800 rpm was 13 hp between the 12-bolt and the 9-inch. At 324 hp for the 12-bolt, this is a difference of 4 percent at that specific data point. If we look at the overall average, the difference is only 2 percent between the 9-inch and the 12-bolt and virtually a push between the S60 and the 12-bolt.

Each rearend required its own specific-length driveshaft. Denny's Drive Shaft built this nitrous-ready, steel, 3-inch tube driveshaft for the Ford 9-inch.
Each rearend required its own specific-length driveshaft. Denny's Drive Shaft built this n
This graph shows the overall torque and horsepower runs for all three rearends. Note how the 12-bolt and the S60 rearends virtually overlap until roughly 5,000 rpm. It would be difficult to see a measurable difference on the dragstrip between the 12-bolt and the Strange S60.
This graph shows the overall torque and horsepower runs for all three rearends. Note how t
We expanded the peak horsepower graph to give you a better idea of the peak horsepower differences among the three rearends. This graph makes the differences look dramatic, but notice that each horizontal line only represents 5 hp.
We expanded the peak horsepower graph to give you a better idea of the peak horsepower dif

What we've discovered is that there is definitely a rear-wheel power difference between a 9-inch Ford and the 12-bolt, which appears to be the difference in hypoid offset between these two rearends. Just for fun, consider that submitting a Ford 9-inch to either the Mikronite or REM gear-treatment process could improve the rear-wheel horsepower numbers. Car Craft did a test last year on a Ford 8.8 rearend ("Mikronite for Power," Jan. '07) using a Fox-bodied Mustang and saw a 6hp increase in rear-wheel horsepower by just treating the gears. When we brought this up to Ray Currie, he mentioned that he prefers the REM process, which creates a similar treatment to the ring-and-pinion gear surfaces that would no doubt produce similar results. That would put the 9-inch on equal terms with a 12-bolt-unless you did the same mod to the 12-bolt. The cost for the Mikronite process on a ring-and-pinion is $275.

Overall, we've learned that the 9-inch doesn't eat as much power as we thought, the 11-inch rear drum brakes for a Ford weigh a ton, the S60 isn't as heavy as we believed, and the 9-inch housing, gears, and axles are only 5 pounds heavier than a 12-bolt, which was a bit of a surprise. Add in the minimal power differences, and we've just placed another piece in the mosaic of the musclecar puzzle. Plus, as with any successful dyno test, it has created as many questions as it has answered. Now we're looking at that TH400 and wondering how much power it eats compared with a TH350. Hmm . . . .