Long-stroke aftermarket crankshafts and large-bore aftermarket blocks are commonplace in modern Pontiac builds. Powerful street engines commonly displace more than 460 cubic inches and are capable of generating 600 lb-ft of torque and/or achieving peak horsepower at an rpm that was once considered unrealistic. Combining such an engine with a manual transmission can make for great fun, but it’s generally far more power or speed than an original Muncie or Borg-Warner four-speed can handle, and complete transmission failure is often reality.
Tremec introduced a modified-for-GM-products TKO-600 five-speed manual transmission in 2004. It was conservatively rated at 600 lb-ft and featured an overdriven Fifth gear to reduce cruising rpm at highway speeds. It was instantly successful and is quite popular with Pontiac hobbyists.
So what’s a guy to do when he wants the advantages of a modern five-speed, but his Pontiac V-8 pushes the limits of a stock TKO-600? American Powertrain in Cookeville, Tennessee, has a solution in its 600Xtreme TKO upgrade. Follow along as we learn the details from a company insider.
This may look like an ordinary TKO-600, but it features American Powertrain’s 600Xtreme op
The Tremec TKO
The Tremec TKO transmission is very reliable and an excellent performer, and its versatility lends to its popularity. Based on the original TR-3550 Ford five-speed, Tremec modified and improved upon its design to create the aftermarket TKO, which is available with different capacity ratings, gear ratios, and spline counts. Companies like American Powertrain subtly modify the transmission case and/or shifter so it fits certain models like the Second-Gen Firebird. Also available is a complete installation kit that includes a custom crossmember, driveshaft, and all associated hardware.
After a specific cryogenic hardening process, American Powertrain REM polishes the transmi
With its 600lb-ft capacity rating, Tremec’s TKO-600 has been a popular choice for use with a high-performance Pontiac V-8. Our past experience with the TKO-600 has been nothing but positive. The gear ratios offer excellent acceleration and performance while reducing cruising speed to improve economy and reduce overall engine wear. Some hobbyists find that the TKO-600 doesn’t always shift smoothly when operating near 6,000 rpm. That wasn’t typically an issue since most Pontiacs built with stock components didn’t operate at such speeds. Aftermarket components have pushed the operating range and power output beyond the capacities of the stock TKO-600, and that can be concerning to some.
The 600Xtreme Upgrade
The TKO is internally shifted, and during the 600Xtreme upgrade, the shift-rail mechanism
American Powertrain picks up where the highly capable TKO leaves off. Its 600Xtreme TKO option increases the torque capacity of the TKO-600 by 350 lb-ft and improves shifting up to 7,500 rpm. And it accomplishes it without compromising synchronization or shifting performance at low speed.
“We didn’t want to take anything away from the basic goodness of the TKO, which is our bread and butter transmission because it is so capable right out of the box,” explains American Powertrain owner Gray Fredrick. “Our goal was to tweak the box to get every bit of performance possible from it without negatively affecting driveability.”
The 600Xtreme-prepped TKO is assembled to “race tolerance” during the process.
So what makes the 600Xtreme special? Starting with a new TKO-600, a single American Powertrain technician in its craftsman-type shop completely disassembles and reassembles the transmission to ensure the build is consistent and thorough from start to finish. During disassembly, the parts are separated and sorted into those that are reused and/or reworked from those that are replaced.
The existing 4616-alloy gears, shafts, and shift forks are exchanged with identical pieces that have been cryogenically hardened to improve strength and performance. The controlled process includes slowly reducing the components to –300 degrees F for more than 12 hours with liquid nitrogen to improve molecular consistency, adding as much as 30 percent more strength to the original alloy without affecting its tolerances. “We specify that our parts be rapidly brought to a high temperature to maximize the effects of the cryogenic hardening process,” Fredrick adds.
The optional billet-aluminum White Lighting shifter features a short throw and adjustable
For about $3,200, American Powertrain can supply you with its ProFit TKO-600 kit that incl