To 5-speed or to 6-speed, that is the question when looking at the different TREMEC manual transmission options to put in your car or truck. How do you choose?
The TREMEC TKX 5-speed transmission with its smooth, precise shifting and small case has become the go-to for classic muscle cars and trucks. It is also finding its way into a lot of late-model and racing vehicles as a smaller, lighter and more economical option.
The TREMEC Magnum 6-speed is the gold standard for manual transmissions with amazing high-RPM shifting, strength and gearing range to transform the driving capability of any car or truck. And it includes a double overdrive with the option of .5:1 final ratio. The variations of the Magnum – the Magnum-F and Magnum XL – also provides additional shifter locations.
Let’s dive into the most common items that people weigh when considering whether to choose the TKX 5-speed or Magnum 6-speed for their vehicle build.
Fitment
ABOVE: Classic muscle cars are notorious for having narrow transmission tunnels that make fitting a modern manual transmission in place of the original 3- or 4-speeds and automatics difficult. It often requires cutting and enlarging the tunnel for proper fitment. The TREMEC TKX 5-speed transmission was developed to make it easier for owners of classic muscle cars and trucks to upgrade to a modern, world-class manual transmission without having to do major transmission-tunnel modifications.
The first thing to consider is whether the transmission will physically fit in the car or truck. Muscle cars from the 1960s have transmission tunnels that are notoriously narrow since the automatics and manual transmissions of the time didn’t need a lot of room to fit. Designers also wanted the smallest transmission hump/tunnel possible to provide the most interior space.
The TREMEC TKX 5-speed was designed to fit classic car and truck transmission tunnels, in many instances without cutting and modifying the tunnel. The TKX has a maximum width of 10.5-inches compared to the maximum width of the Magnum 6-speed at 12.25-inches. That’s a 2.25-inch difference in width, and the Magnum requires more space above the mainshaft which also affects fitment in the tunnel.
For most cars built before the 1990s, the Magnum 6-speed will require transmission tunnel modifications for fitment. However, it is such a popular swap into a wide variety of cars and trucks, that several of our Elite Distributors offer partial or whole replacement transmission tunnel panels that make it easier to fit the Magnum.
By the 2010s, most rear-wheel-drive vehicles including SUVs and trucks were available with very large automatic transmissions which require a large transmission tunnel that will fit a Magnum 6-speed.
If in doubt about what might be required for either the TKX and Magnum in a specific vehicle, contact one of our Elite Distributors who will have details and possibly solutions for each transmission.
Bellhousing
The TKX can be bolted up to a factory GM or Ford four-bolt bellhousing common from the 1950s through the early 1980s. It is available with a coarse- or fine-spline input shaft so in some cases even the original mechanical clutch can be reused if desired.
If installing a Magnum 6-speed into one of these 1980s or older vehicles, a new bellhousing and clutch system will have to be sourced, and some applications may also require conversion to a newer, smaller gear-reduction-style starter. With some aftermarket bellhousings and scattershields, a Magnum can be used with a mechanical clutch system like muscle cars originally had. However, it is very common to upgrade these muscle cars to hydraulic throwout bearings when upgrading to a Magnum transmission.
Shifter Placement
Another common question relating to fitment is the shifter placement. For bench-seat vehicles, it is important to have the shifter come through the floor in front of the seat while owners of cars with center consoles prefer that the shifter position is close enough to original to retain the console.
For starters, the TKX 5-speed has 3 possible shifter locations: 19.52, 16.75 and 12.68 inches behind the bellhousing mating surface. The shifter is centered on the transmission. This will require an offset shifter available from some Elite Distributors for specific applications to allow the use of original muscle-car shifter holes and consoles.
The Magnum 6-speed is available with a total of 4 shifter locations. The original Magnum offers shifter locations of 21.05, 17.53 and 13.25 inches behind the bellhousing mating surface. Some Elite Distributors offer shifters and other accessories to help place the shifter in the correct location for a number of specific vehicles.
Additionally, the Magnum-F was designed specifically to fit 1998-2002 LS1-powered Camaros and Firebirds/Trans Ams, fitting the transmission tunnel and locating the shifter in the stock location. It has provisions for third- and fourth-generation F-body factory torque arm mount cast into the tailshaft housing. It can be swapped into 1993-1997 LT1-powered Camaros and Firebirds/Trans Ams with minimal extras needed. The shifter location is 23.89 inches behind the bellhousing mounting flange.
And the Magnum XL is an extended-length version of the Magnum, designed for 2005-up Ford Mustangs and 2010-2015 Chevrolet Camaros which originally came with semi-remote shifters. The Magnum XL shifter is 28.46 inches behind the bellhousing.
ABOVE: You can find graphics with key measurements of the TKX and all three variations of the Magnum including the shifter locations in this article.
Engine Output/Transmission Strength
ABOVE: Torque input ratings are a confusing topic for many potential customers. In the aftermarket, there is no standard for this rating. As a manufacturer of transmissions for global auto makers, TREMEC uses the standards developed for car makers which are extremely conservative compared to aftermarket applications.
There are two primary ratings when it comes to power-handling capability of transmissions. The first is the torque-rating. As an OE manufacturer, TREMEC uses ratings consistent with car manufacturer standards to rate our aftermarket transmissions like the TKX and Magnum. That means that the transmissions are rated to work without issues at the rated power levels for 100,000 miles or more.
The TREMEC TKX 5-speed transmission has a rated torque capacity of 600 lb-ft while the Magnum series has a 700 lb-ft rating. For extreme racing with significantly higher engine output, some TREMEC Elite Distributors offer upgrade packages for handling increased torque.
The second consideration is maximum engine RPM. For classic engines, the TKX max RPM shift rating of 7,500 is almost always more than enough. But for higher-winding later engines like the Ford Coyote DOHC V8 it might be a limitation, making the Magnum 7,800 RPM shift rating a better solution. For racers, the shifting RPM is definitely a factor to consider.
Expected Use
ABOVE: Knowing what you plan to do with your TREMEC-equipped car or truck is crucial to choosing the right manual transmission. If you plan on autocrossing or other types of racing and also want to drive your vehicle on the street, the Magnum 6-speed with its double overdrive allows you to install a lower rear-axle-gear ratio for performance on the track but still be able to keep the engine RPM low for highway cruising.
What are you going to do with your TREMEC 5- or 6-speed equipped vehicle? The intended driving purpose is extremely important when choosing your manual transmission. Is your car or truck just going to be used for street cruising? Or street and racing duty? What type of racing? Or only racing and no street use? Maybe you have serious autocrossing and some road course track days planned? Having an honest idea of what you plan do to will help ensure you choose the right TREMEC transmission.
Both the TKX 5-speed and the Magnum 6-speed have optional wide and close ratio gear sets allowing the end user to choose the best one for their use. The Magnum gets an advantage over the TKX with its extra overdrive gear, allowing for very low rear-axle gear ratios and still having realistic street and highway cruising capability.
ABOVE: If your plan is for street cruising with occasional dragstrip use, the TKX 5-speed is a great choice. The TKX has 3.27 and 2.87 First gear options so you don’t have to run as low a rear-axle gear ratio. The TKX also has a choice of .68, .72 or .81 5th gear Overdrive so you can cruise at highway speeds without lugging the engine down too low.
Part of the usage equation is also the engine you’re choosing and what its powerband will be along with typical shift RPM. It’s ideal is to pick a transmission with gearing that will have you shifting at or near your engine’s peak power output. Yes, it’s time to dust off those math skills, but have no fear; using the TREMEC Gear Ratio Calculator makes it easier.
You can try multiple tire sizes, axle gear ratios and specific TREMEC transmission gear ratio sets to see what the engine RPM will be in each gear at specific road speeds. You can take this data and compare it with your engine’s camshaft profile and powerband to see which gearing will have you shifting at optimal RPM and the MPH in each gear. You can also see what the streetability will be like with cursing engine rpm at various road speeds. This part is especially important for overdrive consideration, and literally double important with the Magnum 6-speed and its double overdrive.
The Cool Factor
We would be kidding ourselves and you if we didn’t acknowledge that there’s a cool factor in choosing between a TKX 5-speed and a Magnum 6-speed.
The TKX is plenty cool, raising the bar on the manual transmission experience for anyone driving a car with a transmission more than 20 years old (that’s around 2004 for those of us who still think 1970 when we hear “20 years ago”). It provides good First gear ratio options, very highway friendly Overdrive gear options, and its size makes it easy to install in just about any rear-wheel-drive vehicle. What’s not to love?
Some people need to own the biggest, baddest and the best. While the TKX is extremely good, there’s no doubt that the Magnum is bigger with a higher torque rating and even more gears and gear ratios. Plus the bragging right of a double overdrive.