1968 Chevrolet Chevelle SS - Put It Into Overdrive!

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.)

Rick invited us down to the Gear Vendors company headquarters in El Cajon, California (near San Diego), where his crew installed one in our Street Sweeper '68 Chevelle project car. What's interesting to note is that a Gear Vendors installation is remarkably simple. Even with photos, we were out in about five hours. (Try that with a five-speed manual swap.) But you don't have to go to Cali to get one installed-there are certified Gear Vendors installation facilities all over the country. (You can check the Web site or call to find one in your neck of the woods.) In fact, in order to sell a Gear Vendors overdrive, a retailer must be a qualified installation center for the entire Gear Vendors product line.

The short of it: For just under $2,600, you can get a kit for your Turbo 400-equipped GM A-body. Another $750 or so gets it installed for you (it's about $100 less for Camaros and Firebirds), which also includes the cost of shortening your driveshaft. Many Gear Vendors kits are available for Ford and Mopar musclecars, too, and that includes kits for four-speed manuals. While we were there, we got the chance to sample a late-model C5 Corvette, a '32 Ford street rod, and a '56 Chevy truck with a Gear Vendors overdrive, and they were all just as fun to drive.

Yeah, we said "fun." We didn't really expect that an overdrive button could be so cool, but it was a blast to chirp the tires by clicking it on. Likewise, turning it off on the highway, into a non-overdrive passing gear, was a thrill, too. And the icing on the cake: blasting through all the gears, splitting them with the overdrive (that's six in all for our Turbo 400-equipped Chevelle). It was so fun, we almost forgot the initial impetus for going overdrive: better gas mileage.

A careful measure of fuel economy before and after the Gear Vendors installation revealed that even under ideal conditions (55-mph top speed, no full-throttle blasts), the best we could muster on the highway without overdrive was 7.5 mpg. After the install, we easily pulled down 10 mpg, and we were going way faster than 55 mph, more like 65 mph. That's an improvement of 25 percent. Put another way, we could go the same amount of miles from our fill-up for about 20 bucks less-and still have 5 gallons left in the tank. The only question we're asking now is: "Why didn't we do it sooner?"

The Beauty Of Gear Splitting
The first thing most people think about when contemplating the purchase of a Gear Vendors overdrive is the improved fuel economy. The thought coming just after that is imagining what it would be like to extend the life of a high-performance engine by another 25 percent before needing an expensive rebuild. If the credit card isn't out by then, you're a really tough customer, and you may also need to ponder the improved quality of the driving experience that allows you to, say, hold a non-screaming conversation with a passenger, or listen to the radio at a reasonable volume level. We would also like to offer you another reason: gear splitting.

In a drag racing scenario, it is the average power applied over time-rather than fuel economy-that trumps all else. In a perfect world, the drag racer would keep his engine at peak power continuously for the entire run to maximize his e.t. But that can't happen, partly because the transmissions in use behind high-powered engines tend to be simple, beefy two-speed Powerglides, or three-speed Turbo 400s. These transmissions can take loads of abuse, but their limited number of gears necessarily forces the engine out of its optimal operating range at some point.

Enter the Gear Vendors overdrive. For our purposes here, we can take the overdrive concept and turn it on its head. Whatever numerical rearend gear ratio that was optimal (without overdrive) for peak power going through the top end can now be multiplied by a factor of 1.28 for even more grunt off the line. (If you were using a 3.73 gear, a 4.88 gear will now give you close to the same finish-line rpm.) At the point where you run out of gear without the overdrive, kick it into overdrive for the dash to the finish line right in the meat of your power curve. The end result is that your engine stays near its peak longer-and quicker e.t.'s and faster trap speeds are the outcome (you may even find yourself needing only a nominally shorter gear as a result).

But the advantage doesn't end with just having an overdrive. Try splitting the gears between one-two (and two-three if you have a three-speed like a Turbo 400 or Ford C4). You'll stay near peak power for even longer, for improved e.t. Don't believe us? We found Jim Luttrell, a veteran Super Comp racer from Apache Junction, Arizona, using a Gear Vendors overdrive in just such a fashion-with race-winning results. We spoke with Jim about his experience racing a dragster at over 200 mph with a Gear Vendors overdrive, and here's what he had to say:

"I run a Powerglide, and we've worked to split the gears with our Super Comp dragster. For a while, I was just using it as an overdrive to bring the rpm down-to bring it back into the torque curve-at the top of the track. Then we moved to NHRA Super Eliminator in NHRA Division 7, and with the Gear Vendors, we were the only Dragster in the division running over 200 mph on a 7.90-second index-right at 204 mph. With the gear splitting, you take off in First gear, then at a set rpm, the Gear Vendors goes into First-over, with the Gear Vendors engaged. When the transmission shifts into Second-which is High gear in a Powerglide-the Gear Vendors will switch back out. Then later on down the track, the Gear Vendors comes back in to keep the rpm down in the engine's torque peak. It basically makes a two-speed Powerglide into a four-speed.

"We then figured out how to use an MSD rpm-activated switch with a lock on it, and also on the shifter, with another rpm-activated switch. The shifter on the Powerglide and the shifter on the overdrive are not connected-the rpm switch on the shifter turns the overdrive on, and the one on the MSD turns it off. Basically, I don't have to do anything. If there's some human involvement, it isn't going to be consistent. In Super Comp, consistency is the key to winning. The reason why the lock is so important is that on the top of the track, I want the overdrive to stay engaged to where if something happens, I don't want to over-rev the motor.

"Then we wanted even more simplicity, so we stopped using the rpm switches and changed over to timers to activate the overdrive. We still had the switch on the air shifter to deactivate the overdrive on the one-two shift. We also used a second timer to engage the overdrive on the top end. It gave us more consistency. After a few runs on a test and tune day, we could easily move any of the shift points before race day. We did pretty well. We actually won a Wally Award with it in Super Eliminator at the National Open in Division 7.

"I'm making right around 1,900 hp, and this Gear Vendors unit has never come apart, or been checked out. It's still together. I couldn't even guess how many passes I put on it-it's got a minimum of at least 400 passes. It's been in at least three different dragsters since 1997, and behind everything from a carbed big-block Chevy, to a blown Keith Black Hemi. Rick Johnson at Gear Vendors keeps wanting to take it apart and inspect it, but I don't see any reason to. Those guys have just been above and beyond for me."