Five Speeds or Six?
Hurst includes reproduction...
Hurst includes reproduction GM "621" bellhousings with its kits, but set us up with an optional Quick Time SFI unit. Before installing the clutch, Jarvis tightened the bellhousing to spec and attached a magnetic dial indicator to the crank to check for runout. Hurst recommends a maximum of 0.005 inch of runout, which ensures that the input shaft of the trans will align properly in relation to the crankshaft. As it turned out, the bellhousing was positioned too far toward the 8 o'clock position, so it was moved closer to the 2 o'clock position using offset dowel pins. Jarvis attributes the initial misalignment to poor manufacturing tolerances when the Olds block was originally cast.
In addition to the three different trim levels offered by Hurst Driveline Conversions' kits-Basic, Deluxe, and Elite-Hurst offers a choice of either a Tremec 500 or 600 five-speed, or a T56. To help Pro Touring aficionados decide between them, here's a quick breakdown of what each has to offer. The Tremec TKO 500 and 600 are an evolution of the TR-3550. These extremely stout gearboxes are rated at 500 and 600 lb-ft of torque, respectively. While the TR-3550 was designed to work in concert with meager stock V-8s, the TKOs feature larger gears, tapered roller bearings, a beefed-up case, an internal three-rail shift system with cast-iron forks, 4615 alloy steel gears and shafts, a stronger single-piece countershaft, and a short-throw billet shifter. Furthermore, the TKO has provisions for eight different shifter locations, three crossmember mounting locations, and electronic and mechanical speedometer pickups. The TKO 500 has a deep 3.27:1 First gear, while the TKO 600 has a 2.87:1 First, which accounts for the difference in torque capacity. There's also an option to choose between a 0.64:1 and a 0.82:1 overdrive on the TKO 600, while the TKO 500 has a 0.68:1 Fifth gear. We opted for the taller 0.64:1 overdrive ratio with Project Olds, as we felt the 0.82:1 overdrive was intended more for road race applications. Factoring in its strength, versatility, and affordability, the TKO is the most popular aftermarket Tremec overdrive by a large margin.
For those who need two overdrive ratios, the T56 Magnum is the new king on the hot rod block. A new and improved version of the venerable T56, this is the same transmission used in new fifth-gen Camaros and C6 Corvettes. Tweaks include larger input and output shafts, larger and stronger gears, an improved heat treatment process, a stronger case, double- and triple-cone synchronizers, laser-welded dog teeth, stronger shift forks, and shorter throws. The result is an astounding 700 lb-ft torque capacity, which is more than enough to handle the healthiest of big-blocks. For added versatility, the Magnum has multiple shifter locations, mechanical and electric speedometer pickups, and is compatible with both cable and hydraulically actuated clutches.