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A Supercharger and Overdrive
Tim Graves; via Bucks County, PA:

By:Jeff Smith
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A Supercharger and Overdrive
Tim Graves; via Bucks County, PA: I’m looking for a supercharger and a TH350 with Overdrive for my daily-driven Cutlass. So far I have a rebuilt ’75 Olds 455. With 0.030-over pistons, a ported Port-O-Sonic manifold, ported Edelbrock heads, a 0.544-inch lift cam, a 750-cfm street D carb, and a serpentine accessory drive kit. The exhaust consists of Hooker Super Comp headers and a 3-inch exhaust through Hedman cross-pipes that leads to a pair of 3-inch, 50-series Flowmasters. I run a 2,800- to 3,200-rpm stall converter with the TH350 leading to a 12-bolt 3.73:1 Chevy posi rear. The biggest, widest BFGoodrich drag radials I can fit are approximately 28 inches tall.The front suspension has QA1 coilovers along with tubular upper and lower front control arms and Edelbrock rear shocks.

I cannot find any superchargers for an Olds 455. I’m also looking for an overdrive for my TH350 because I max out the rpm before I get to the end of Atco’s quarter-mile dragstrip. Best run a few years ago was 13.42 spinning the tires off the line, with no Second gear, and still had to let off the throttle before crossing the lights at the end of the track. I’ve been debating changing the 3:73:1 to a 3:42:1 or just getting a new trans with overdrive. I cannot fit any tire bigger than what is in there now. One last thing, I also have hand controls, because I’m a paraplegic. Where can I find more power for my Cutlass? I don’t want nitrous or turbos.

Jeff Smith: While Oldsmobile engines are well known for their torque, I’ve always thought a centrifugal supercharger package for an Olds would make major power (if you could hook it to the ground) and you wouldn’t have to spin the engine really hard to get there. Plus, the centrifugal supercharger would be hidden underneath a stock or near-stock hood. Alas, no one as yet builds the mount assembly for a Procharger F2 or Vortech centrifugal, so I went looking at more conventional 6-71- or 8-71-style Roots superchargers and a couple of companies that offer impressive aluminum lungs for a 455 Olds.

The first company I tried is perhaps the best known—Blower Drive Service (BDS) in Whittier, California. BDS offers a manifold, a drive kit, and an 8-71 supercharger in pieces that quickly added up to more than $5,200, and that’s before we talk about a pair of carburetors, linkage, air cleaners, scoops, and ignition. So we’re talking some serious coin here. I also found a company called Superchargers USA located in La Habra, California, that sells a complete Olds 455 kit for a 6-71 supercharger with an 8mm drivebelt kit for around $4,400, but again, you’re going to need the aforementioned accessories. You might consider a main web support girdle if you lean on this thing, and I wouldn’t recommend any kind of power-adder unless the engine has forged pistons. If you have hypereutectic or cast pistons, you’re just asking for trouble. Blowers make heat, heat makes pressure, but heat also makes the engine more detonation prone, and detonation will turn cast pistons into piles of scrap in milliseconds. Ask me how I know.

Also, I’m surprised that a TH350 trans has survived behind your 455 for any length of time. Generally the standard trans is the TH400. You might consider stepping up to the larger TH400 trans for durability. Of course, if you’re going to buy a transmission, you might consider a 4L80E. It is a late-model electronic version of the TH400 with the same First-Second-Third gear ratios as the TH400 (2.48:1, 1.48:1, 1.00:1) but with an added overdrive of 0.75:1. The only problem with these transmissions is they are much heavier than typical TH400s, but worse, a new one will run more than $2,000 with a converter and you still have to purchase a separate controller that generally costs anywhere from $500 to almost $1,000. These controllers allow you to easily manipulate up- and down-shift points, shift firmness, line pressure, and several other parameters, but at the aforementioned cost. Most of these units are controlled via laptop computer software, which, while not difficult to learn, may be more technically challenging for some. You will also need a throttle position sensor to make most of these systems function.

Another option that might be best is the Gear Vendors overdrive unit. Gear Vendors has been making a bolt-on extension for many automatic and manual transmissions that incorporates a very rugged overdrive planetary system that will produce a 22 percent (0.78:1) overdrive in high gear. This virtually duplicates the 4L80E overdrive but does not require a black box/computer to operate. The biggest hassle is fitting the 12 1?4-inch-long and 7-inch-tall overdrive unit underneath the floor pan of your ’75 Olds. The good news is that the later-model cars added more elbow room for the TH400 compared with the ’64 through ’67 A-body cars, so the overdrive should fit without too much difficulty. Even if you left the 3.73:1 rear gears in the car, the overdrive would produce an equivalent final drive ratio of 2.90:1. Frankly, most mild Olds and Pontiac engines don’t respond well to deep gears because these engines like a taller gear such as the 3.42 or even a 3.31:1 gearset if you could find one. Combining the 3.42:1 ratio with overdrive becomes the equivalent of a 2.66:1 rear gear, which might be close to ideal. With a 26-inch-tall rear tire, cruising rpm in overdrive would be a little more than 2,400 rpm. That’s nice because you could just roll in on the throttle at that speed and that big Olds would pull forever. Consider changing the rear gear regardless of whether you go with an overdrive. Those big Olds motors use torque to accelerate the car, and a deeper gear adds leverage that isn’t necessary. Small-block Chevys need gear to get them moving; big-block Olds motors don’t need the extra leverage.

More Info
Gear Vendors; El Cajon, CA; 800/999-9555;

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