Gear Vendors Overdrive

Increased performance always comes with a price. In the case of hot rods built primarily for acceleration and without the aid of a modern overdrive transmission, the price is the compromise of excessive highway engine rpm and the poor mileage and engine wear that comes with it. Many people swap in a late-model overdrive transmission, but even more are content with their setup of a good old-school three-speed auto or four-speed stick. A Gear Vendors (GV) overdrive is the mechanical amends for excessive highway RPM and short dragstrip gearing. It is designed to bolt directly to the back of most popular automatic and manual transmissions, and it will also handle as much power as you can throw at it. The price is a tad stiff compared to a late-model junkyard trans swap, but eliminating compromise does not come cheap-a complete GV overdrive kit will set you back about $2,400.

There are two main benefits of a Gear Vendors overdrive, and one of them is actually performance. But first, let's look at the reason most people turn to a GV-the overdrive "highway gear." The Gear Vendors unit revolves around the robust Leycock-DeNormanville planetary overdrive, which GV claims can handle 1,200 hp and comes with a warranty to back up the claim. The overdrive ratio is 0.78:1, making a 4.11:1 rear gear behave like a 3.20:1 gear when you engage the GV. Likewise, 3.55:1 gears cruise like 2.77 cogs. The ratio is a straight 1.0:1 when not engaged. The overdrive ratio is generated by a 77-tooth ring gear acting through planetary gears upon a 22-tooth sun gear. Parasitic loss is less than 1 hp per 400, efficient by any standard, let alone automotive transmissions where internal loss can run over 20 percent. Low drag also means low heat, so the unit holds just 28 ounces of oil whether it's a street car or an 850hp trophy truck running the Paris-Dakar rally. The GV input shaft is 300M high-tensile axle steel, and the all-important tailshaft coupler is 4130 high-tensile. The output yoke is a Dana 1350-series performance unit.

There is also a potential performance benefit to a GV unit, since it basically doubles the number of gears you have available and allows a few clutchless shifts with manual transmissions and the potential of ratio splitting on automatics. Use a GV with a manual trans like an M21 and your one-two shift requires no clutch operation-bang the button and you're in Second. The stock gearset on that box is 2.20, 1.64, 1.28, and 1.00:1, so that's a step from 2.20:1 to an overdriven 2.20:1, which equals 1.71:1, meaning less rpm drop between gears than if you just went from First to Second.

The shift is firm like a prepped automatic, but there is lag time between when you hit the button and when the unit actually shifts, so coordinating shifting manually while engaging/disengaging the GV unit is very difficult. GV president Rick Johnson says it can be done, but we've never been able to master it. The effect is similar with a three-speed automatic, and because automatics have wider ratios, actuation of the overdrive can be done in each gear-First, First-OD; Second, Second-OD; Third, Third-OD. Your three-speed auto therefore becomes a close-ratio six-speed. With more shifts, the engine RPM can be kept in the fat of the torque curve. Gear Vendors claims that its mildly built W-31 Cutlass (with a 3,000-stall converter in a TH350 and 3.42:1 rear gears) dropped from 14.7 in the quarter to 13.42 by adding the overdrive. Of course, that assumes you are coordinated enough to hit the button at the right time to avoid "hunting" caused by the delay time. In years past, we couldn't manage a smooth run through the gears, so GV developed its AutoShift Sequencer to make it easier. See the sidebar in this story for more info on the Sequencer.

With the standard electronics that come with the GV unit, activation can behave automatically, like a factory overdrive, switching on in high gear at the preset 47 mph and off at lower speeds. The driver can also select "Manual" and use overdrive at any time via a cockpit switch, typically mounted on the shifter or via a secondary headlight dimmer switch on the floor. The electronics package is set at the factory when the product is ordered-consumers specify gearing and tire size to be used. Gear Vendors will flash a new chip for $35 should vehicle specs change. Included in the supplied software package is a program called AutoLaunch, which is capable of popping the vehicle into First-OD at a preselected speed, getting you 28 percent farther down the track before a one-two clutch shift.