Drag Reduction
Zack Farah: "Heavy-duty transmissions require more power to turn, but this effect can be reduced through careful parts selection. Using Torrington bearings in place of T-washers between counter-rotating components reduces parasitic drag, as does setting up clutch packs with extra clearance in First and Second gear. The low-reverse clutch pack needs extra clearance because it produces the most parasitic drag of all components in the transmission. The trade-off is a rough Reverse engagement, but that's usually not a big deal with performance transmissions."
Stanley Poff: "In an effort to reduce parasitic power losses in a transmission, Torrington bearings have become very popular lately. Additionally, aluminum lightweight internals, gun-drilled or barrel-drilled shafts, and steel components that are manually lightened are some of the items used in class index style race vehicles such as Super Stock, Competition Eliminator, as well as the Outlaw 10.5 style cars."
GM Trans Lineup
Zack Farah: "The Powerglide, TH350, and TH400 each have their pros and cons in terms of price and performance in both street and race applications. The Powerglide is a two-speed design that is the ultimate in low weight, low drag, and high strength. This makes it very well suited for big-block powered drag cars. The Powerglide is the only transmission in history that can be completely built from the ground up using only heavy-duty aftermarket components, and it can easily handle 2,500 horsepower. The obvious downside is that its two speeds don't make it very street friendly. A TH350 can be built to handle 700 horsepower, and works great in small-block applications. We usually recommend the TH400 for big-block powered street cars, as it can be built to handle 850 horsepower. For any given power level, the TH400 is cheaper to build than the TH350, but it also requires more power to turn."
Regis Finn: "Powerglides are a good choice for race cars because there are a variety of performance parts available in the aftermarket. You can build a strong budget Powerglide or an all high-end Powerglide with no problems at all. Since it's a two-speed transmission, however, it's not desirable for street use. The TH350 is a good choice for both street and race applications, but is limited to what it can handle. With a small budget you can get one to handle 450 hp. If higher hp capacity is required, it can be very costly. That said, the TH400 is the best all around because with just a few upgrades it can handle high-hp applications and still be very streetable."
Achilles Thomas: "The Powerglide is very old trans and should only used for drag racing applications in vehicles that are more concerned with track times than fuel economy. It can also get very expensive when built for high-horsepower drag racing applications. As for the TH350, it is great for small-block applications, very cost effective and reliable, and there are plenty of affordable aftermarket parts for it. The TH400 is one of, if not the strongest transmission to ever come from GM. It's great for racing applications, heavy-duty trucks, and big-blocks with lots of torque. You can find these units built at a fair price depending on their expected use. The 700-R4 is our most popular transmission due to the streetability offered by its four speeds. It's easy to swap into older cars that come with Powerglides, TH350s, and TH400s. Likewise, it offers great fuel economy and performance. There really isn't a downside to this transmission."
Shift Firmness
Zack Farah: "Balance in shift firmness is primarily a matter of personal preference. Smoother shifts are comfortable and produce very little shock to the drivetrain; a daily driver would benefit such an application. Firm shifts reduce clutch pack wear, but transmit greater shock loads to the drivetrain, U-joints, axle splines, and body mounts. It's all a balancing act based upon the car's intended use, and the durability of the rest of the drivetrain."