The Pros and Cons of Installing 4.10 Gears
Ford Mustang enthusiasts know that to be a serious threat at the drag track, it is necessary to upgrade your gearing to at least 4.10 gears. Most late model Mustangs and many other sports cars come equipped with standard 3.55 gears in their rear differential, however by adding 4.10 gears they can effectively make their drag times faster and deliver more power to the wheels faster.
What Is All the Fuss over Gear Ratio?
Gear ratio has a great deal to do with how your car performs and handles under load. The gear ratio is the ratio of how many times your engine has to turn the crankshaft to turn the rear wheels one rotation. Therefore, the higher the ratio (4.10 gears compared to 3.55 gears) the higher the gearing and the greater number of rotations before the rear wheels turn. This equates to a greater amount of power transferred to the wheels. Late model Mustangs and sports cars tend to have a lower gearing to accommodate more highway driving, however this can cause them to feel sluggish or slow on the track. In many instances, a simple fix is to install 4.10 gears with the stock motor of the Mustang which should "wake up" the feel of the Mustang on the track, but still provide highway drivability.
The Pros to 4.10 Gears
The obvious pros of installing 4.10 gears is that the car's performance will improve on the track, but with negligible effects to the highway driving. If your car is equipped with an overdrive, you may not even notice a difference in gas mileage with the new higher gearing. Depending on the transmission that you have installed, you might even be able to adjust the overall gearing so that the final drive of your car is nearly the same while in overdrive, but allows you to take advantage of the new gearing in the lower transmission gears.
The main negative aspects of installing 4.10 gears lie in performing transmission modifications in general. If the gearing in your differential is changed in a significant way, then the speedometer calibration is likely to be affected which will make your speedometer inaccurate. The new gearing can affect transmission shift points as well (on automatic transmissions, but this is a non-issue for manual transmissions). Custom tuning by a qualified speed shop is normally a good fix for both of these issues.
The final con associated with 4.10 gears is obviously a drop in fuel economy. Switching from a gear set of 3.55 or 3.73 to 4.10 gears will affect your gas mileage slightly as your engine will be turning more times to rotate the rear wheels once. In most cases you can expect to see a drop of 1 to 2 miles per gallon, but in many cases fuel economy was never a concern for performance enthusiasts anyway.
Installing 4.10 gears is an effective way to wake up a stock sports car and making it a real contender on the drag track on the weekends, but still able to be used as a daily driver too.