May 24, 2011


Our second category is the street/strip category. We would deem this name appropriate for all of the cars/trucks running with a good amount of horsepower, say in the 450- to 600hp range. This name would also be appropriate for the street racers who like to take it to the track as well. In this category, drag radials and slicks will start to play a role.

Right off the bat, you can eliminate the T-5. It just won’t hang too long with a lot of horsepower. Other than that, the rest of the transmissions that we talked about earlier would probably fit the bill nicely.

When the need to speed/power shift shows itself, a good upgrade to all of these transmissions would be an aftermarket shifter. The factory shifters (with exception of the Richmond boxes) don’t have adjustable stops, nor are they spring loaded. A nice aftermarket shifter like the Steeda Tri-Ax, Pro 5.0, or the MGW, will make slamming the gears a breeze on the Tremec boxes. On the Top Loader, you can use a Hurst Competition Plus, or even a Hurst Super Street or Long shifter if the transmission tunnel will give up the room.

If you’re dealing with more than 600 hp, don’t give up hope on the Tremec boxes. The T-56 will still hold what you got and the TKO 500/600 boxes can be easily upgraded. Treatments are available that will increase the capacity of the TKO 500/600 by approximately 15 percent. There are also modifications that can be done to the gear cones, synchronizers, and shift forks to help hit the right gear at the right rpm.

Options for the Powershifter

Depending on how hard-core of a racer you are, there are also some hard-core modifications that can be done to all of the transmissions that were mentioned above. The gears can be either face plated or pro shifted, which eliminates the synchronizers and allows you to row through the gears without fear of missing one. All of the gearboxes that we have discussed can be modified in this same manner.

After deciding which box will physically hold your engine, the rest of the choice boils down to price, how close you want to stay near factory/stock, and if your particular vehicle will easily accommodate an aftermarket transmission

After deciding which box will physically hold your engine, the rest of the choice boils down to price, how close you want to stay near factory/stock, and if your particular vehicle will easily accommodate an aftermarket transmission. A lot of owners are eager to switch to an Overdrive transmission, or a transmission that will withstand a lot of power, but they’re not so eager to yank out the angle grinder and start cutting on stuff.

When you’ve made up your mind on the above questions, then you need to sit down and decide which transmission fits the rest of your combination the best. Let’s look at an example:

Your 347ci SBF runs 205cc heads, 11:1 compression, and a solid roller cam that puts the hp peak up around 7,000. It likes to idle (or tries to) at 1,200 rpm. As an engine builder, this author sees a lot of street cars running around with combinations such as this. When you lug a smallish engine down to 1,600-1,800 rpm with a cam that doesn’t become efficient until after 2,000 rpm, you get the buck. Now, with that low rpm buck or a lack of throttle response at low rpm, would you want to pair your car with an Overdrive that has you cruising at 1,600 rpm?

The combination also depends on the rearend ratio, what size tires you’re running on the back, and more. However, the principle still applies here: Match the transmission gear ratios with the overall setup of your vehicle.

Conversely we have another example: Your 496ci FE is running aluminum heads, 9.5:1 compression, and a hydraulic roller cam that peaks at about 5,200 rpm. It idles at 750 rpm with barely a lope and pulls like a tank right off idle. You could pair this engine up with a transmission that has an 0.82:1 Overdrive or a 1:1 high gear ratio, but if the rest of the car’s driveline parts were all installed with one idea in mind, there would be no reason not to equip the transmission with an Overdrive that would allow the car to cruise at a low rpm. Again, building a car where all the parts work together is a blessing.

All this same information applies to the transmission’s First gear ratio. A 5.0L Mustang with a 4.30-geared rearend probably wouldn’t like the 3.27:1 First gear of a TKO 500. On the flip side, a ’64 Galaxie with a 3.00 rearend wouldn’t take nicely to the 2.32:1 First gear of a close ratio Ford Top Loader.

Let’s come full circle with the conclusion. If you’re looking for advice on which manual transmission to buy, the first thing to consider would be the budget. Once you figure out how much money you can throw at toys, try to pair the transmission with the horsepower/torque that you plan to make. There’s no use in spending $1,500 on a transmission when you will break it the first time you introduce your right foot to the firewall. If you can make a logical selection up to that point, then the last choice will be based on matching the transmission’s characteristics to the rest of the vehicle. After that, it’s all smooth sailing.