Rearend Gear Swap & Air Filter Performance Test

Do Speed Parts Really Work Edelbrock Intake And Carb Making Horsepower

Rearend Gear Swap
Price: Gear swap only, with bearings and stuff: $305.85; TSD differential and gears: $669.95
E.T. Gain: 0.645 second/1.3 mph

Swap lower-ratio gears into a car and chances are good that it'll get across an intersection much quicker. But go too low (numerically higher) and you may overrev the engine at the top-end, cut your cruise rpm, and kill gas mileage. If you have those concerns, then gears like 4.10s are probably out of the question. You may want to swap to slightly lower cogs, but will a slight change really make a noticeable difference in performance?

Our '66 Mustang was the perfect candidate to show the effectiveness of such a change. It runs a 5.0L EFI engine and AOD overdrive trans, and we started with stock 2.80:1 gears in the 8-inch rear. Surprisingly, a change to still-freeway-friendly 3.25:1 gears and a limited-slip made it measurably quicker. The difference can really be felt on the street, and the track-test results are shown below. For testing, we stalled-up the car at the starting line to about 1,500 rpm and shifted at 5,500 rpm. Wheelspin on all runs was minimal running on P225/50HR15 BFGoodrich Euro TA tires. -Miles Cook

Other than a set of JBA headers, a GT-40 intake, and a 65mm throttle body, the SVO 5.0L crate motor in this '66 is bone stock. The car's AOD trans and converter are also untouched.
Other than a set of JBA headers, a GT-40 intake, and a 65mm throttle body, the SVO 5.0L cr
Currie Enterprises has all the goods for freshening up Ford 8-inch rearends, including a Torque Sensing Differential (TSD) that was added while the rearend was apart. New 3.25:1 gears for Ford 8-inch diffs are currently unavailable, and Currie stocks used gears-inspected used sets-in various ratios. Later this year, Currie will have new gears on the shelf in a number of 8-inch ratios.
Currie Enterprises has all the goods for freshening up Ford 8-inch rearends, including a T
Two types of 8-inch carriers are used in Mustangs. The earlier '65-'67 carriers did not have the reinforcing ribs as shown here. This heavier-duty version is what was used in '68-and-newer Mustangs and the ribs are easy to see to the right of the driveshaft.
Two types of 8-inch carriers are used in Mustangs. The earlier '65-'67 carriers did not ha

Performance Testing
Description	ET	MPH	Improvement
2.80:1 gears	14.921	96.02	Baseline
3.25:1 gears	14.276	97.32	-0.645 sec/+1.3 mph

Source
Currie Enterprises
Dept. CC
1480 B North Tustin Ave.
Anaheim, CA 92807
714/528-6957

Do Speed Parts Really Work Paper Air Filter Vs K&N Air Filter

Both air filters were new, 14x3 inches in size, and used the same top cover and bottom drop-style base. In testing, the engine was warmed to the same temperature and the shifts were made at the same point. The result: the K&N filter provided a 0.092-second e.t. reduction. Sure, it's only about a 0.10-second drop, but considering the install ease and cost, it's a worthwhile upgrade.

Both air filters were new, 14x3 inches in size, and used the same top cover and bottom dro

Aftermarket Air Filter Test
Price: $36.95 filter only (PN E1650), $56.50 complete filter assembly (PN 60-1280)
How Much Faster?: 0.092 second/0.81 mph
Although stock paper-element air filters do a fair job of trapping dirt, they're not well-noted for high-cfm airflow as needed with a hi-perf engine. According to aftermarket companies, upgrading to a high-flow aftermarket filter not only filters the air better, but generates more horsepower. In the Mar. '96 issue we put this to the test on K&N Engineering's Dynojet chassis dyno by back-to-back testing a traditional paper filter versus a same-sized K&N filter. According to the dyno, our engine pumped out 6 more horsepower with the K&N unit. Although our old 355 small-block was up 6 hp, we decided to drag-test our Cheap Street Chevelle with its new 502 big-block to see if the filter actually made the car any quicker in the quarter-mile.-John Kiewicz