Installation of TCI 6X Six-speed transmission in project “MaxStreet” Chevy II

If four forward gears is good, six must be better, right? That is what TCI is thinking, with the release of their 4L80E-based 6X six-speed automatic high performance transmission.  For our powerTV Project MaxStreet Nova II, the 6X was right up our alley.  We needed a transmission that can handle 850hp+ that will be produced from our Edelbrock/Musi 555 big block Chevy and F2 Procharger, while cruising at low RPMs on the highway as well.

Your transmission is arguably the most important piece of the drive train puzzle for your race car, high performance muscle car, or any vehicle for that matter.  You might have a well-built piece up front making a ton of power and the strongest rearend components money can buy, but if you can’t reliably pass that energy between the two, you aren’t going very far. Along with the added durability that is always key when selecting a transmission, the actual performance of your vehicle is directly related to the transmission that you mate with your engine.

For those of us that are drag racing-minded and want to get out of the hole quick, the low gears are important.  But on the very same token, you want to have the overdrive that will allow you to cruise at highway speeds.  Tied within is your fuel mileage.  If you’re rumbling along the interstate in high gear with the tachometer pegged, you’re probably going to get pretty familiar with gas stations.

A Look Back at Popular GM Transmissions

For these reasons, overdrive transmissions have been very popular inventions for performance automobiles.  They afford the ability to run low rear gears, thus somewhat having the best of both of both worlds with tire-smoking launches while still having some top end speed and highway drive-ability.  GM has had several overdrive transmission offerings for its cars and trucks.  The Turbo-Hydramatic (THM) family of automatic transmissions was developed and launched in 1964 with the Turbo-Hydramatic 400 in Cadillacs and Buicks.  Various modified forms of these transmissions in the aftermarket are still in use in street and strip applications today.

The TH400 transmission – known as the Turbo 400 by drag racers and auto enthusiasts – is an incredibly durable three speed automatic transmission.  It’s a well-traveled piece in racing and high horsepower street applications for its gearing and strength, however, as a three speed, it isn’t very conducive for street and strip applications where a higher cruising speed on the road is desired.  Despite this limitation in highway driving ability, people with cars pumping out a lot of horsepower had to sacrifice the top end speed for the strength of the Turbo 400.  This classic beat out other GM performers such as the tried-and-true 700R4 that doesn’t  take the punishment that it receives from powerful, tire-smoking, wheel standing vehicles very well.

The 4L80E transmission was developed in the 1991 as the successor to the popular Turbo 400.  The 4L80E is a high performance unit that in many ways combines the attributes of the Turbo 400 and the 700R4/4L60E into a very attractive, very strong, and flexible package.  It offers the durability of the Turbo 400, with the additional benefit of an overdrive fourth gear and is fully adjustable to suit any need or application.  The transmission was manufactured for use in Chevrolet and GMC pickup trucks, vans, SUVs, and commercial vehicles.

It incorporates many of the very same internal components that were used in the Turbo 400, but has the extra overdrive fourth gear and uses electronics – the very first Hydramatic to incorporate electronic controls – to control the firmness, shift points, and other setup attributes.   About 75 percent of the 4L80E’s internal parts are either shared with or interchangeable with the Turbo 400 unit, and the bell housing bolt pattern and flexplate are identical to the 400.  Thus, it bolts up to any GM small block or big block like normal.

Being an electronically-controlled transmission, many older cars that lack a computer to control it.  However, for the carbureted applications, a work-around to the electronics is a throttle position sensor that is mounted to the carburetor.  Many of the standard methods involving the valve bodies and springs for achieving desired shift firmness are still used internally, but much of the work of the transmission relies on the computer. The 4L80E is, naturally, a big, heavy piece of machinery.  Despite that fact, it still fits in most GM muscle cars with only slight modifications for clearance, making it a popular choice for racers and many of the hot rods and muscle cars on the street that sport modern nuances.

TCI’s Take on the 4L80E – The 850 HP Capable 6x

The 4L80E is, by all accounts, a great transmission.  It’s built to take some punishment and it accomplishes what most car guys need: a healthy balance of the low end and big end.  But like anything, it can be made bigger, better, faster, and stronger.  And TCI Automotive, the leader in performance transmissions and converters, has done exactly that with their newest high performance offering, the TCI 6X Six Speed Automatic Transmission.

The TCI 6X transmission is the world’s first automatic capable of handling 850 horsepower, and uses the latest developments in drivetrain technology for pro-touring, street, and all-out race vehicles.  It features six forward gears and fully programmable automatic or manual shifting for improved acceleration and fuel economy at cruising speeds.  TCI’s Scott Miller explained, “Our goal was a strong Turbo 400-type transmission that would handle the horsepower and load but give customers the overdrive where they can cruise down the highway with a big motor.  We started toying around with it to see what we could do and once we got to talking to consumers that would potentially buying something like that, they wanted it. People wanted a six-speed that was an automatic that was a lot more durable than the GM six-speeds and they didn’t have to worry about a clutch.”

The TCI 6X is based on the 4L80E design from GM, but provides the best of all words with its great fuel economy, low first and second gear for some quick motivation, and a high horsepower rating.  While based off of the 4L80E and using it’s case, that’s essentially where the similarities and sharing of internal parts ends. TCI has completely redeveloped the GM piece, opting for strength in every area of its design and components, such as the planetaries and valve bodies.

One of the primary areas that sets the 6X apart from its GM brethren is the clutch packs.  To achieve the extra gears, TCI has increased the clutch capacity to six overdrive clutches – two more than the 4L80E – by modifying the clutch plate, the piston, and performing other machining processes.  The valve bodies started out as stock cores from GM, but some additional machining and changes to the OEM parts affords this trick new transmission its two extra gears.

The planetaries in the 6X utilize Alto Red Eagle clutch packs, which are the very same material found in TCI’s ProX Turbo 400’s that are rated for 2,500-plus horsepower drag racing applications.  TCI manufactures the gear stands in all of their transmissions, opting with billet steel material in the 6X that gives it its strength. “Most people, when doing a different planetary for a 4L80E-based transmission, it’s a piece that they take from an OEM setup from different transmissions,” continued Miller. “But we make it in-house on our CNC.  It’s what really increases the strength of the piece.”

The 6X features a 2.97 gear, with gears that are slightly smaller than its predecessors to make it as strong as possible.  The transmission is rated to withstand the torment of upwards of 850 horsepower, but is perfectly capable of more than that, which TCI is quick to admit and we’re hoping to prove. “We advertise 850 horsepower, we have some applications that have more than that,” explained Miller. “The capability is there and it can definitely handle more.  We set it at 850 mainly so that if someone is manually shifting it and they leave it in high gear and try to take off with a lot of horsepower, it’ll smoke it.  Of course any application that could happen. But we have to put some kind of rating on it, that way we cover the bases.”

The TCI 6X has many other internal features and modifications that make it a superior piece in the strength department.  The feed for the overdrive fourth gear clutch, which is a bolt with a hole in the center that feeds fluid to the clutch pack when the gears are changed and the clutch packs are disengaged is very small from the factory, and when increased in size, becomes weaker.  TCI has beefed up the feed with a larger, custom-made bolt made from a much stronger grade A material. It also sports a heavy duty, high-energy type kickdown band.

TCU – Controlling your TCI 6x

Like the 4L80E, the TCI 6X six-speed is fully electronically controlled through a Transmission Controller box and the pre-loaded software. Once a customer receives the unit, all that’s needed is input of the gears and tire sizes.  The controller is completely programmable, offering the ability to control all of the shift points, converter lockup for gears 2-6, all of the line pressures for each gear, and switching between automatic and manual mode.

Manual mode can be deployed with the simple flip of a switch on the TCU, thus allowing the 6X to be manually shifted with a paddle shifter or with TCI’s Outlaw shifter with a bump switch.  To do so, you put the transmission in fourth gear, flip the switch, and it starts out in low gear and can then be bumped up through each gear.  And your vehicle can be shifted in that manner forever with the 6X…a big plus for those that enjoy manually shifting.  The software also has shift calibrations that provide the ability to create different profiles of shift points for different uses; one for street and another for the race track, for example.  Every transmission is dyno’ed following production with the Trans Controller box and wiring harness to ensure that everything in the electronics department is in working order.

Any 10 or 12-inch style torque converter can be mated to the 6X. TCI has a variety of combinations ready in the 10-inch models for stall ranges, but custom combos up to the 4500-5000 range can be accommodated if needed.  And, while based off of a GM transmission for GM engines, TCI has kits available to bolt the 6X up behind both Ford and Chrysler motors.

Installation into Project MaxStreet Nova II

To put the TCI 6X transmission to the test, we’ll mate it up with the 555-cubic inch, Procharged, Pat Musi-prepared engine under the hood of our project “MaxStreet” 1966 Chevy II. Once bolted up, we’ll put the transmission through its paces and outline our experiences with all that the TCU unit offers.

What’s in the kit:

–       6X transmission

–       transmission control unit

–       TCU wiring harness

–       Dipstick

–       Paddle shifter

–       Transmission Cooler

–       MaxShift Transmission Fluid 3 Gallons

The TCI 6X comes standard with gear ratios of 2.97, 2.23, 1.57, 1.18, 1.00, 0.75, and 1.76.

The TCU is programmed with a start up calibration file for the 6X, but some basic inputs are required for each application prior to use of the transmission. These inputs include the rear gear ratio of the vehicle, tire diameter, the type of tachometer input, and throttle position calibration at both idle and wide open throttle. The TCU’s onboard Setup Wizard will prompt you for this information upon startup. While all of the TCU functions can be controlled via a personal laptop, it is not a requirement. TCI offers an optional Touchscreen Monitor/Programmer for programming and offers monitoring capability of all transmission functions along with other digital and analog inputs. For our Nova, we have utilized the Monitor (part #377525) and mounted it in the center of the dash for easy access, while the TCU itself is mounted on the firewall under the dash.

TCI has included software for your computer that explains all of the tranmission and TCU features and provides detailed instructions on proper tuning.

TCI's Transmission Control Unit and Touch Screen Monitor

The connector at left is the Transmission Input Speed Sensor (TISS), the topmost for the Transmission Output Speed Sensor (TOSS), and the larger plug at bottom is the main harness connector.

There are four connections that are required for proper use of the TCU unit, and all are clearly marked for ease of installation and setup. The first is the power source, which should be connected to a 12V source. Secondly, the ground wire should be – if at all possible – connected to your battery ground. The third is the TPS wire, which, if you are installing the 6X transmission into a vehicle that doesn’t have a throttle position sensor, you must install one. If you are installing the transmission behind a fuel-injected engine, however, you can use the existing sensor. The last connection is the RPM input wire, which can be connected to your ignition box RPM output wire.

The TCI 6X and 10-inch TCI Pro-X torque converter, ready to be mated up and installed.

Any OE-type 4L80E converter will fit the 6X transmission, but Scott was very adamant about advising all customers to speak with a TCI sales technician for recommendations on the proper converter for your specific application. Prior to installing the converter, you will want to examine the splined couplings, the mating surfaces of the engine block and the dowel pins. After determining everything is in good shape, coat the surface of the converter hub with a film of automatic transmission fluid, and pour a quarter of transmission fluid into the converter. Carefully install the converter while supporting the weight to avoid damage to the front pump seal.

The transmission tunnel in our Chevy II wasn't quite large enough to accommodate the size of the TCI 6X, thus it needed to be opened up and both widened and lengthened so that we could carry on with the install.

Once the converter is installed, we bolt the transmission up to our 555 cubic inch Big Block.

As with any transmission install, you want to perform some initial checks for cracks in the flexplate, excessive wear in the drive shaft yoke, and make certain that the converter bolt pattern matches the flexplate.

Installation of the 6X transmission is a rather basic and routine undertaking. Once mounted on the dowel pins, check the converter for freedom of movement and complete the install by applying Loctite to the bolts and tightening to 30 ft lbs. At this point you will want to install the TCI Trans Cooler (part #820500). In our Chevy II, we have mounted the transmission cooler on the radiator. After doing so, attach the shifter linkage arm to the 6X and put in neutral and install the cable/linkage. Attach the cooler lines and tighten to 12 ft. lbs. Fill with 4 quarts of transmission fluid and start the engine, running through each gear with a light throttle with the rear wheels off the ground. Once complete, check for leaks in the cooler lines and radiator fittings. The total fluid volume will depend on your converter selection, cooler, and transmission pan.

For our Nova, we chose the TCI Thunderstick Outlaw shifter to mate with the 6X. In order to manually shift all six gears, the shifter must be left in the overdrive position and the Manual/Automatic mode programmed into the TCU must be utilized. To do so, the manual/automatic wire needs to be connected to the activation switch.

The TCI 6X Transmission represents a great new offering for the performance vehicle market. It offers a great level of added strength and durability for your high horsepower and high torque applications over existing OEM and similar transmissions, while sporting many great features, the least of which is the fully programmable Transmission Control Unit. Throw in the extra two gears for a much more practical solution to maintain low-end power and cruising speed and the added fuel mileage that goes with it, and the flexibility for automatic or manual shifting, and you have one great package from TCI.

About the author

Andrew Wolf

Andrew has been involved in motorsports from a very young age. Over the years, he has photographed several major auto racing events, sports, news journalism, portraiture, and everything in between. After working with the Power Automedia staff for some time on a freelance basis, Andrew joined the team in 2010.
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