May 24, 2011

If you’ve spent any time at all hanging around the various online forums, you’ve seen the obligatory, Which manual transmission should I use? post. Most often, the poster wants a street/strip setup; something that will be easy to drive on the street but yet could withstand a few launches at the local dragstrip. We all want that, right? We all want something between the T-5 that’s in Dad’s ’93 Mustang GT and the Jerico that we see on YouTube getting the absolute snot beat out of it at the dragstrip.

The choice isn’t always so simple and that’s what we’re going to discuss in this article. Just like a camshaft or an intake manifold, there are a myriad of choices and they all hinge on several very key facets of your particular build. We’re going to break down the most common scenarios (street, street/strip) for you and then list the most common options under that scenario. You’ll notice that as we get toward the racier applications, the options will get fewer and more specialized. As an aside, we’ll only be including commonly available aftermarket transmissions. Otherwise, you’d still be reading this article next month.

Street/Cruiser

The first category, and probably most common, would be the street/cruiser category. This would encapsulate the daily drivers, and the guy with the super-sweet, restored ’67 Mustang fastback that never gets above 55 mph or 2,500 rpm.

For cars with engines under 350 hp/350 lb-ft, you pretty much have everything open to you as an option. This would include the Tremec T-5, the Tremec TKO 500/600, the Richmond 5/6-speed, the Tremec Magnum T-56, and for you old-schoolers, the Ford Top Loader. We know you’re saying, You said you’d only include aftermarket transmissions. Why are you mentioning the Top Loader? Well, there are many aftermarket Top Loader venders out there, offering everything from spice to nice, and we’ll talk more about that a little later.

For you guys with more horsepower, you can check yourselves against the comments that we will add beside each transmission in the notes below. For the most part, you want a drivetrain that will be able to withstand what your engine will put out. Since we’re talking about street cars only, we’ll assume that no one with drag radials or slicks will be in this category.

Tremec T-5

The T-5 has been around for a long time, offering reliable performance in various vehicles such as the Ford Mustang, Chevrolet Camaro, Pontiac Firebird, Chevrolet S-10, and more. Earlier versions were rated for less than 310 lb-ft of torque, while the new T-5 that you can get from Tremec is rated at around 330 lb-ft. While there are aftermarket gearsets available, the most common gear ratios for the T-5 include a 2.95:1 First gear and a 0.63:1 Overdrive. The input shaft is 1116x10-spline.

Pros:

    1. Very light at 75 pounds
    2. Great shifting transmission, quick and smooth
    3. Large variety of aftermarket shifters available
    4. Pretty cheap for a new gearbox
    5. Comes with its own factory shifter

Cons:

    1. Only rated for 330 lb-ft. We’ve seen stock 5.0L Mustangs break them

Tremec TKO 500/600

The TKO 500/600 is an absolute workhorse when it comes to passenger-car transmissions. The 500 and 600 denote how much torque the transmissions will hold. The key here is that it’s rated in continuous torque, so the TKO 500 can handle 500 lb-ft all day long. These transmissions replace the older Tremec 3550 and 3550-TKO transmissions that looked pretty similar, but didn’t have the torque ratings that these transmissions have.

The TKO 500 is available with two different input shaft choices: 1116x10-spline and 118x26-spline. The latter increases the torque capacity of the transmission, but Tremec doesn’t list a separate torque rating for that option. For gear ratios, First gear is a 3.27:1 and Overdrive is a 0.68:1.

The TKO 600 is available only with a 118x26-spline input shaft. It is, however, available with two different Overdrive ratios, 0.82:1 or 0.64:1.

Pros:

    1. Medium weight at 105 pounds
    2. Large variety of aftermarket shifters/handles available
    3. Will handle a large amount of horsepower/torque
    4. Many different shifter positions available (up to eight), so you can put the shifter where you need it
    5. Short input shafts available so that you can use a TKO with an older Top Loader bellhousing
    6. Comes with its own factory shifter. It also has a mechanical speedometer provision, along with an electronic speedometer provision

Cons:

    1. Doesn’t like to be shifted quickly at higher rpm due to manufacturing tolerances and design
    2. Larger than a Top Loader or T-5, so transplanting this into your older muscle car may necessitate some modifications. For instance, to achieve the proper pinion angle in an older Mustang, the bracing inside the transmission tunnel may need trimming or a little persuasion. On some older Galaxies, the transmission tunnel has to be completely rebuilt

Richmond 5/6-Speed

The Richmond transmissions have been around for a while. Before the TKOs came along, they were essentially your only choice for a five-speed box that would handle some abuse. What’s unique about them is that unlike the Tremec boxes, the Richmond transmissions still use an external shift linkage like the old muscle car transmissions. This can be a pro or con, depending on which way you look at it.

In a Ford model (because that’s the only one that matters, right?), the Richmond 5-speed is offered in a Street version and a Road Race version. Both of those are offered with a Top Loader-depth input shaft or a longer input shaft, to be used with a deeper bellhousing. The input shaft can be either a 1116x10-spline or a 118x26-spline. Rated at 450 lb-ft of torque, the Street transmission has a 3.28:1 First gear and a 1:1 Fifth gear (no Overdrive). The Road Race trans has a variety of gear ratios to choose from.

There is also a 5-speed Super Street transmission from Richmond. It’s rated for 600 lb-ft of torque and is available with the same input shaft dimensions and gear ratios as the older 5-speed.

The 6-speed ROD is pretty similar to the 5-speed Super Street, except that there is an Overdrive available. The ratio of that Overdrive is dependent on which gearset you order the transmission with.

Pros:

    1. Smaller overall size to fit in the transmission tunnel of most cars
    2. Lots of gear ratios available
    3. Comes with a Long shifter

Cons:

    1. Pretty expensive for a five-speed or six-speed gearbox. As a matter of fact, they are the most expensive transmissions of our lineup today
    2. External shifter linkages, which may need set up and adjustment
    3. Depending on the rearend ratio, the transmission gear ratios may or may not fit the bill for younot having an Overdrive can be a deal breaker for some, while others with numerically low rearend ratios can benefit from the low First gear

Tremec Magnum T-56

This punk of a transmission is rated for 700 lb-ft of torque. Yep, 700. The Ford version of the transmission comes with a 118x26-spline input shaft and two gear ratio choices: a 2.66:1 First gear, 0.62 Sixth gear; or a 2.97:1 First gear, 0.50 Sixth gear. Like a TKO, the shifter positions are changeable, which will allow you put the shifter up in the transmission tunnel where you need it to be.

Pros:

    1. Will handle an enormous amount of torque
    2. Lots of different shifter positions and aftermarket shifter options
    3. Has both mechanical/electrical speedometer provisions
    4. Comes with its own factory shifter
    5. Even a version for the S197 platform available
    6. Did we mention it will hold 700 lb-ft of torque?
    7. Six forward gears (if you need them)

Cons:

    1. Very heavy and long
    2. One of the more expensive transmissions
    3. May need modification/fabrication done to the midplate for use with some clutch kits, like the McLeod/RAM twin discs

Ford Top Loader

The Ford Top Loader (called the Top Loader because you load the guts in through the top) has been around since the ’60s. There’s a reason for that: It’s one tough gearbox. Available in two different input/output shaft sizes, the 1116x10-spline (small input) or the 138x10-spline (big input); two different flavors (wide ratio or close ratio); and a wide selection of physical sizes and shifter locations, the Top Loader could fit in everything from a 289 Shelby Cobra to a big-block Galaxie. While only being a four-speed, old-school gearheads still love the beefy design and strength of the Ford Top Loader. This author has never seen an official torque rating for the Top Loader, but experience would provide a rough estimate of 500 lb-ft for the small input version, while the big input could handle 600 lb-ft.

Pros:

    1. Will handle a lot of torque
    2. Can be made to fit a lot of different car platforms
    3. You can find good usable cores or rebuildable cores for not a lot of money
    4. Can easily rebuild with a few tools and some patience
    5. Small overall size, will fit in a lot of transmission tunnels including Fox Mustangs

Cons:

    1. Pretty heavy, all cast-iron case/tail housing
    2. No Overdrive
    3. External linkage shifter that needs set up and adjustment

Street/Strip

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.