The real joy of owning a muscle car is in driving it. Muscle car owners who want to get the most out of their cars often drive to distant car shows or other events, but without an overdrive transmission, a long road trip becomes tedious. If the car has a performance rear axle ratio, it’s even worse. I love the sound of a V8 at high revs as much as any other, but 3600 RPMs going straight for three hours straight with a noisy exhaust is tiring. Most of us have gotten used to being able to carry on a conversation and/or listen to the radio on long trips, and wish we could drive past at least a couple of gas stations without stopping to refuel! An overdrive transmission solves those problems and provides many other benefits as well.

The Tremec TKO is a five-speed manual transmission with overdrive that is ideal for retrofitting classic muscle cars from the 1960s and 1970s. With your choice of an overdrive ratio of 0.82:1, 0.68:1, or 0.64:1 depending on the model, you can really get those revs down to a manageable number. Lower engine RPM on the highway offers several benefits.

First of all, as already mentioned, there is the noise level. If you have a 3.73 axle ratio with a 235/60-15 tire (26.1″ tall), 75 MPH equates to 3600 RPM with four speeds without overdrive. The TKO-600 with a 0.64:1 fifth gear (the version most popular) will drop that 3600 RPM to a quiet 2300 RPM at the same 75 MPH.

Another benefit of lower RPM that I already mentioned is better fuel economy. All things being equal, the engine will obviously use less fuel at 2300 RPM than at 3600 RPM, but with a high-performance car engine that has been built for performance, there is another factor that comes into play. At 3600 RPM, some 4-barrel carbs may have secondaries partially open. If you have a steeper axle ratio, the secondaries are even more likely to be open at highway speeds. With a 4.10 rear gear, that 75 MPH number I’m using results in almost 4000 RPM with a non-overdrive transmission. At that time, many carburetors will have the secondary barrels discharging fuel. Reducing the RPM needed to cruise on the highway will reduce the throttle angle, closing the secondaries and making a big difference in fuel economy. In fact, I’ve seen fuel consumption double on the highway when installing a TKO, due to being able to cruise without having the secondaries open!

Engines wear out faster at higher RPMs. In simplified terms, each motor has a useful life consisting of a certain number of revolutions, barring abuse, neglect, or catastrophic failure. If you use less than those revs every time you drive 200 miles to a car show, your $5,000, $10,000, or even $20,000 engine will last longer. This will be everything that is attached to it and that rotates with the motor. Your alternator, water pump, mechanical fuel pump, power steering pump, and AC compressor will turn at lower RPMs on the highway and their lifespan will increase.

High performance engines produce more heat than normal passenger car engines. Many muscle cars have heat problems due to high RPMs on the highway. Reducing RPM with an overdrive can reduce engine temperature and prevent overheating on long trips.

The intangible advantage of all of the above is that overdrive will allow you to drive your muscle car more. It will and will be more likely to drive you to car shows further afield, or even on vacation! Overdrive allows you to enjoy your car more by driving it places you wouldn’t consider going with its 4-speed motor (or 3-speed automatic) cranking the engine at 3600 RPM.

The TKO is pretty strong for most muscle cars. It is rated for 500 or 600 lb.-ft. continuous input, and those numbers are very conservative. There are a lot of cars out there that run well above rated torque with the TKO, and failures are rare. Although I officially cannot condone using the TKO in an application that exceeds the torque capacity rating, I can tell you from experience that many people have done it and have had no problems, even under race conditions.

The Tremec TKO will decrease the noise level on the road, increase fuel consumption, increase the life of your engine and everything related to it, could reduce or eliminate temperature problems and allow you to drive your car to places where I would. with an old four-speed. It is stronger than the old Muncies, T-10, Toploader and A-833. Versions are available that will bolt directly to a stock GM or Ford 4-speed bell, and custom Mopar bells are available to retrofit a TKO to a Mopar small-block, big-block, or late-model Hemi. All in all, it’s an ideal transmission for a highway-driving muscle car. For more detailed information on TKO specs and options, check out my other articles in this series.