Street SweeperAt $4.27 per gallon for 91 octane premium unleaded, the price to fill up the 20-gallon tank in our '68 Chevelle just climbed well over $80. Yikes! On top of that, the actual distance yielded by that gas with our 496-inch big-block and Turbo 400 trans was only about 150 miles. We'll do the math for you: That's about 7.5 miles per gallon. Something had to give, so we contacted the overdrive specialists at Gear Vendors.
We'd heard good things about Gear Vendors overdrives from friends and readers. For one thing, we'd lose none of the strength of our bulletproof TCI Turbo 400 like we might if we switched to a 700-R4, 200-4R, or 4L60E. We'd need none of the complicated programming electronics like we would for a 4L80E or 4L60E. We wouldn't need to break out the chopsaw for tunnel clearance either-only a slight massaging of the tunnel with a rubber mallet would be needed. Traditional overdrive automatics also hunt worse than Elmer Fudd-and that ride is no fun on the highway. We could've gone with an overdrive five- or six-speed manual, but neither of these was right for the street/strip vibe of our Chevelle. The Gear Vendors was our obvious choice, so we made the call.
We spoke to Rick Johnson, the CEO of Gear Vendors, and he told us in no uncertain terms that his 0.78:1 overdrive unit would better our fuel economy by at least 25 percent. Not only that, but his overdrive would be practically indestructible-even behind our big-block-and loads of fun to boot. (Rick's a big fan of splitting gears, which the Gear Vendors overdrive allows because its ratio is split numerically perfect between most transmissions' gears.)
The Gear Vendors overdrive...
The Gear Vendors overdrive kit for the Turbo 400 had everything we needed to add a pleasant 0.78 overdrive to our big-block '68 Chevelle. The kit costs $2,595 (PN 3D0400AFS), and includes everything except labor and a shortened driveshaft.
The guts of the Gear Vendors...
The guts of the Gear Vendors overdrive: A bulletproof mechanical pump at the front of the housing (right) supplies pressure to engage a conical clutch that engages a planetary gearset residing inside an annulus. It's essentially impossible to break, but the practical limit is right around 1,600 hp-not because that's where they're weak, but because the transmission in front of it usually breaks. Sounds like our kind of piece!