One of the best upgrades to happen to classic musclecars, right next to the modern engine swap, is the automatic overdrive transmission swap. While internal gearing for automatics has not necessarily been an issue, the added element of overdrive is a big hit, especially with higher horsepower engines. With modern transmissions offering up to a .65 overdrive gear, that means less Rs on the engine at freeway speed, which in turns means better economy and increasing engine longevity.

Performance Automatic is one of those companies that provides classic musclecar owners with the alternative to frequent fuel stops with a selection of custom built performance GM transmissions for both modern and classic engines. And as great as that is, there’s one area that Performance Automatic can take your GM transmission a step further: close-ratio planet gears.

Fresh off the press is the announcement of its new Close Ratio Power Planet for GM 700R4, 4L60E, 4L65E and 4L70E transmissions. If you’ve ever raced your classic musclecar with one of these transmissions, you’ve noticed that there’s a bit of a gap between first and second gears. It’s great for off the line performance, but with today’s higher horsepower engines, a lower first gear of 3.06 tends to be a bit too low. Second comes in at 1.63, and even that is tightened up with the Close Ratio Power Planet kit, bringing first and second gear to a much closer 2.84/1.55 configuration.

This combination delivers better performance and consistency in a racing environment. In a recent release, Performance Automatic said, “Other features include a six-pinion design with increased durability, it keeps the engine in optimal power band on 1-2 and 2-3 shifts and it allows a longer pull in first and second gears. No special tools or machining is required when installing the Close Ratio Power Planet.

To find out more details on the close ratio planet kit, visit the Performance Automatic website and be sure to follow them on Facebook for updates and information.