We've heard average estimates of around 15 percent for most street cars, but based on these tests, that might be a bit low for an average. It appears that this average-power-loss number will change based on the specific automatic transmission used, with a greater percentage loss for the heavier, less-efficient units. This probably deserves a closer look into the efficiencies of different automatic transmissions. The bottom line is that there's rear-wheel power to be gained by paying attention to those details.
| Test A |
| Small-block Ford 357 ci in a ’63 Mercury Comet with an AOD automatic, a 9-inch rear, and a 3.50 gear. |
| RPM | Flywheel | Rear Wheel | Difference | Differential |
| Power | Power | w/o fan |
| TQ | HP | TQ | HP | HP | % | HP | % |
| 2,500 | 384 | 183 | - | - | - | - | - | - |
| 3,000 | 410 | 234 | - | - | - | - | - | - |
| 3,500 | 420 | 280 | 270 | 180 | 100 | 26 | - | - |
| 4,000 | 426 | 325 | 304 | 230 | 95 | 41 | 85 | 37 |
| 4,500 | 413 | 353 | 297 | 254 | 99 | 39 | 83 | 32 |
| 5,000 | 389 | 371 | 277 | 265 | 106 | 40 | 88 | 33 |
| 5,500 | 344 | 361 | 254 | 266 | 95 | 36 | 76 | 29 |
| | Avg. | 99 hp | 36.4% | 83 hp | 32.7% |
| Test B |
| Chassis Dyno Fan Comparison |
| RPM | HP | HP | Difference |
| w/fan | w/o fan | HP | % |
| 3,600 | 222 | 235 | +13 | 6 |
| 4,100 | 281 | 298 | +17 | 6 |
| 4,700 | 310 | 329 | +19 | 6 |
| 5,200 | 321 | 343 | +22 | 7 |
| 5,900 | 299 | 318 | +19 | 6 |
| Avg. | +18 hp | 6% |