Maximum-Strength Performance Automatic Transmissions - CHP How It Works
Top Industry Pros Explain The Art Of Building Maximum-Strength Performance Automatics
From the October, 2010 issue of Chevy High Performance
By Stephen Kim
Photography by Stephen Kim
As confused as Blue Oval and Mopar fanatics may be in their misguided hot rodding proclivities, at least they know a good automatic transmission when they see one. How else can you explain the overwhelming number of Outlaw 10.5 Mustangs running Powerglides and mega-buck Pro Touring Mopars equipped with 4L60 overdrives? While GM has continually set the gold standard for swap-worthy powerplants-whether they're Rat motors, 350 Chevys, or LS small-blocks-the engineers in the transmission department have never played second-fiddle to the guys in the engine shop. As a testament to the inherent brilliance of their original designs, the Powerglide and TH400 have been staples of on-track competitors for 60 and 50 years, respectively. Likewise, the 700-R4/4L60E has already been in production for nearly 30 years, and it gets better with each of GM's successive iterations.
Advances in modern friction discs, clutch plates, and lightweight shafts and internals have enabled building transmissions that are more durable and efficient than ever. Furthermore, the recent introduction of GM and aftermarket six-speed automatics means that there are more options available than ever for enthusiasts. With the grueling pace of transmission development, we felt it prudent to sit down with some industry experts to get the latest scoop on current R&D trends. Our cast of pros includes Regis Finn of B&M, Zack Farah of Gearstar, Achilles Thomas of Monster Transmission, and Stanley Poff of TCI.
"High-quality frictions and steels play a large role in the performance of a heavy-duty transmission. Stock applications use paper friction materials and plain steels intended for smooth shifts in daily-driver applications, such as grandpa's '87 Caprice. The most popular brands of performance friction materials are Raybestos' Racing Red and Alto's Red Eagle frictions. For high-performance applications, they afford a greater coefficient of friction between the steel plates and clutch plates. When paired up with Kolene-treated steels, this clutch pack configuration creates the greatest torque capacity per square inch of clutch surface area. In performance street/strip applications with moderate horsepower, we employ the Raybestos Red frictions with Kolene steels manufactured to standard thicknesses. In full-race applications, we use Raybestos/Kolene expanded capacity clutch packs. These are manufactured to a thinner dimension, both the steels and friction plates, so we can fit extra clutches and steels to increase total clutch surface apply area."
Stanley Poff: "The stock friction clutches that come from the factory were designed to have some slippage in them in order to allow the transmission to shift smoothly. The specially designed Red Eagle clutches used by TCI withstand higher temperatures than any other clutch available, in our opinion. We have even worked hand in hand with Alto to develop friction clutches and steel clutches for newer-model transmissions, as well as older transmissions, that are exclusive to TCI. The friction paper in these clutches is saturated in a phenolic resin and then cured. Red Eagle clutches are designed with a softer, more resilient base paper. They're not only saturated in a phenolic resin, but also have a second saturation in silicate. The silicate imparts high heat resistance to the friction paper."
"Heat is arguably the biggest detriment to transmission longevity. Excessive heat in transmissions is detrimental for the same reason as in an engine. Would you hang your engine's radiator off the bottom side framerail of your car? Of course not. With proper cooling, a performance transmission should live for the long haul. Automatic transmission fluid serves many functions in a transmission. It's a hydraulic medium to transmit pressure, sometimes reaching in excess of 250 psi, to apply the clutch packs. Another one of its functions is to transfer torque and horsepower through the torque converter, and this is where 90 percent of heat is generated in the transmission. This is also why ample cooling and airflow over the cooler is necessary. The torque converter is in a constant bleed-and-feed mode. It's constantly recharging with sump fluid and is building heat in the converter. The fluid is then pushed out to the cooler where it must receive adequate cooling and return to the transmission, where it charges the lubrication circuit. This return fluid must lubricate all bearings, bushings, thrust washers, planetary gearsets, clutch packs, lip seals, sealing rings, and the valvebody assembly. After all this fluid has returned to the sump, it goes back to the torque converter and must still be cool enough to allow the converter to transmit torque, and then the cycle repeats. We recommend and insist that a 20,000 GVW Hayden cooler is installed with any transmission up to 400 horsepower, and a 30,000 GVW unit is required for any application above 400 horsepower. We also recommend eliminating any coolers that are integrated into the radiator core, as these are notorious for failure."
Stanley Poff: "Heat is the enemy of transmission performance and durability for multiple reasons. First off, it can break the transmission fluid down to a point where it will no longer perform. When this happens, it is usually a sign that the converter stall speed will go way higher than normal. Secondly, there are rubber seals and O-rings in the transmission that will actually melt or become disfigured to a point where they won't seal any longer. This is why it's imperative to always run a sufficient transmission cooler."
"Installing an adequate transmission cooler increases the longevity of a transmission. Proper fluid temperature is the key to component longevity. When modifying a transmission to operate near peak potential, it is vital to keep [the] lubricant working at its peak performance as well. Heat deteriorates the performance of the parts. For instance, parts can become glazed due to oil breakdown, and seals can become hard and brittle, causing slippage. Choosing the right cooler for your transmission will depend on vehicle type and intended use. If the application is racing, heavy towing, or you live in a hot and dry area, you may need to use a larger cooler. If you're only using a car for street/strip duty, short-distance driving, or mild towing then you may be able to install a smaller cooler."
Stanley Poff: "In a manual transmission, gears slide along shafts as you move the shift lever from one position to another. In an automatic transmission, however, the gears are never physically moved and are always engaged to the same gears. This is accomplished through the use of planetary gearsets.
"The planetary gearsets we use consist of a sun gear, a ring gear, and three or more planet gears, all remaining in constant mesh. The planet gears are connected to each other through a common carrier, which allows the gears to spin on shafts called pinions attached to the carrier itself. One example of a way that this system can be used is by connecting the ring gear to the input shaft coming from the engine, connecting the planet carrier to the output shaft, and locking the sun gear so that it can't move. In this scenario, when we turn the ring gear, the planets will 'walk' along the sun gear, causing the planet carrier to turn the output shaft in the same direction as the input shaft, but at a slower speed to achieve gear reduction.
"If we unlock the sun gear and lock any two elements together, this will cause all three elements to turn at the same speed so that the output shaft will turn at the same rate of speed as the input shaft. This is like a car that's in high gear. Another way that we can use a planetary gearset is by locking the planet carrier from moving, then applying power to the ring gear. This will cause the sun gear to turn in the opposite direction, resulting in Reverse. The clutch pack is used, in this instance, to lock the planet carrier with the sun gear, forcing both to turn at the same speed. If both the clutch pack and the band were released, the system would be in neutral. Turning the input shaft would turn the planet gears against the sun gear, but since nothing is holding the sun gear, it will just spin free and have no effect on the output shaft. To place the unit in First gear, the band is applied to hold the sun gear from moving. To shift from First to High gear, the band is released and the clutch is applied, causing the output shaft to turn at the same speed as the input shaft."
"When it comes to torque converter stall speed, many people miss the mark because proper stall speed is dependent on a wide variety of factors. Based on our experience, the stall speed should generally be set at 300 rpm above the point where the cam lets the engine begin producing its torque curve. This is a good rule of thumb for street performance and driveability. For dragstrip-only use, many more factors must be considered such as body type, class rules, vehicle race weight, tire width and diameter, rear gear ratio, cubic inch displacement, stroke length, compression ratio, carb and manifold type, and all cam specs."
Stanley Poff: "Stall speed selection depends on a wide variety of factors. First and foremost, you must determine if the car is a cruiser, a street/strip machine, or a race car. Once that's established, the weight of the car, ring-and-pinion ratio, engine displacement, and cam lift and duration all come into play. With this information, TCI technicians are trying to dyno the engine in their minds. The goal is to get enough stall to flash near peak torque yet not be too loose and allow the engine to run at high rpm, which will create excessive heat."
Zack Farah: "Racers know that transbrakes help cars launch very hard, but they also help the chassis work more effectively compared to just foot-braking a car at the line. Transbrakes, when engaged, apply two different reaction clutches at the same time, which puts the trans in a bind. This way, the engine is held back and able to be brought up into its powerband without twisting the chassis. The result is a straighter, more controlled launch when the transbrake is released. Additional stress on the trans is irrelevant, as the cleaner launch is the objective. Transbrake packages are available from several sources, and there are several different engineering methods used to achieve the same result. Installing a transbrake requires many internal modifications, much more than a simple shift kit."
"A transbrake works by locking a forward gear against Reverse at the same time through a solenoid, valve, and an electrical switch. Once Low gear is selected, a button fires a solenoid that moves a valve, which brings Reverse on at the same time you're in Low gear. Then at launch, Reverse is released by the solenoid via the valve. Usually this is a specifically designed valvebody and requires upgrades to aftermarket components inside the transmission in order for it to handle the added stress. It may also require port massaging to quickly allow fluid to get where it needs to go."
Zack Farah: "Many muscle car guys are fascinated by GM's new 6L80E trans, but its large size makes it difficult to package beneath a car and it has not had time to come of age just yet. The 700-R4/4L60E needed many years to evolve into what they can be built up to today. About 80 percent of that evolution is attributable to improvements GM made at the factory, and the other 20 percent came from the aftermarket. High-performance billet components, clutch drums, shafts, hubs, flanges, sprag clutches, and shift kits were all developed by the aftermarket. We can expect much of the same for the 6L80E. In the meantime, a 4L80 swap is a good bet for those seeking a bulletproof GM overdrive."
Stanley Poff: "We've looked at the 6L80E inside and out and it is very big, so fitment in older cars would be an issue. Also, the 6L80E hasn't responded to performance enhancements very well. In fact, the engines that they're bolted to from the factory usually incorporate a torque management feature in the ECM programming to limit the stress on the trans and prevent breakage. As an alternative, TCI has developed the 6x Six-Speed. We start with the GM 4L85E and add two gear ratios to it. This is absolutely a dream transmission for street machines. We have installed them behind many 1,000-1,200hp street cars and they hold up great. It is one of the hottest selling transmission and converter packages we have today, and sales continue to increase. Everything is dyno'd and married in our building including the TCU (Transmission Control Unit) computer to control it."
Achilles Thomas: "The pros of the 6L80E transmission are that it's a six-speed automatic, and it's extremely durable. Our website, 6l80e.com, has some basic information regarding this new transmission. Being that it's new, there are a limited amount of aftermarket parts currently available. However, that will be changing in the near future. We also have plans to release a stand-alone computer to operate this trans in older vehicles. The downside of the 6L80E is that it is a fairly large transmission, and most early-model vehicles would require running an engine adapter and computer to operate it."
Zack Farah: "Automatic transmissions are extremely complex devices comprised of dozens of components. In trying to explain how they work, a good place to start is the trans pump, which supplies hydraulic pressure to charge the torque converter and cooling and lubrication circuit, to apply clutch packs, band apply servos, and valvebody control systems. The input clutch drum and input shaft transmit torque from the engine and torque converter to the input element of the planetary gear system. The clutch packs provide a release mechanism for Neutral and Reverse. The direct clutch pack contains the Third gear clutch and houses the intermediate clutch sprag, providing control over the planetary sun gear. They determine whether it will be held for Second gear engagement, driven for Third gear, or serve as reverse input for Reverse engagement. The planetary gearsets consist of two planetary gearsets. The output planetary carrier is linked to the output shaft. The reaction planetary carrier is linked to the low-reverse clutch pack. The reaction planetary is only engaged in Low gear and Reverse, and otherwise it just goes around for the ride. The input sun gear is splined to the forward clutch pack and is applied in all forward gears. The intermediate clutch is engaged in Second gear, but is ineffective for engine braking. Hence, an intermediate brake band is applied in manual Second by a servo for engine braking in Second gear. Finally, the valvebody is basically a hydraulic computer and generates logic for shift patterns via balance valves."
Zack Farah: "At Gearstar, we dyno test every transmission that we build. The importance of testing each transmission is to verify operating pressures, shift points, and overall functionality. The transmission dyno is an indispensible tool for R&D since it facilitates quick removal of the pan and valvebody for recalibration of the valvebody, governor, and shift solenoids. The fluid recovery system on the dyno makes quick and easy work of dealing with 10 quarts of hot transmission fluid. Simulated loads are achieved via an 800-pound flywheel which replicates the inertia of a vehicle weighing 3,000 pounds with a 3.73:1 rear axle ratio. By running a transmission on a dyno we can check for leaks, vibrations, and abnormal noises during a simulated road test. The transmission is observed for leaks at the pump, front seal, speedo housing, rear seal, servo, and accumulator housings. Shift points and shift firmness specifics for each custom-built Gearstar unit are verified on the dyno as well. Any variations in shift timing or shift quality are readily accessible for recalibration on the transmission dyno. For instance, if we experience one shift point which does not occur at the same load-speed setting as the others for that shift calibration package, it's addressed, corrected, and verified upon retest. Transmissions which are shifted via computer or ECM, such as 4L65E and 4L85E, are tested for up to 90 minutes or 120 miles to verify that shift solenoids and pressure force motors will remain functioning properly over the long haul."
Achilles Thomas: "The purpose of dyno testing a transmission is to check that it's working properly, and to watch for leaks and excessive noise. Whether this step is mandatory is up to the trans builder. Monster Transmission actually takes testing a step further and installs each transmission into a test vehicle to drive it either on the street or on our state-of-the-art chassis dyno. By giving our transmissions a real world testing experience, we can fully customize the way the transmission performs and make sure it's working before it leaves our facility."
Zack Farah: "Heavy-duty transmissions require more power to turn, but this effect can be reduced through careful parts selection. Using Torrington bearings in place of T-washers between counter-rotating components reduces parasitic drag, as does setting up clutch packs with extra clearance in First and Second gear. The low-reverse clutch pack needs extra clearance because it produces the most parasitic drag of all components in the transmission. The trade-off is a rough Reverse engagement, but that's usually not a big deal with performance transmissions."
Stanley Poff: "In an effort to reduce parasitic power losses in a transmission, Torrington bearings have become very popular lately. Additionally, aluminum lightweight internals, gun-drilled or barrel-drilled shafts, and steel components that are manually lightened are some of the items used in class index style race vehicles such as Super Stock, Competition Eliminator, as well as the Outlaw 10.5 style cars."
GM Trans Lineup
Zack Farah: "The Powerglide, TH350, and TH400 each have their pros and cons in terms of price and performance in both street and race applications. The Powerglide is a two-speed design that is the ultimate in low weight, low drag, and high strength. This makes it very well suited for big-block powered drag cars. The Powerglide is the only transmission in history that can be completely built from the ground up using only heavy-duty aftermarket components, and it can easily handle 2,500 horsepower. The obvious downside is that its two speeds don't make it very street friendly. A TH350 can be built to handle 700 horsepower, and works great in small-block applications. We usually recommend the TH400 for big-block powered street cars, as it can be built to handle 850 horsepower. For any given power level, the TH400 is cheaper to build than the TH350, but it also requires more power to turn."
Regis Finn: "Powerglides are a good choice for race cars because there are a variety of performance parts available in the aftermarket. You can build a strong budget Powerglide or an all high-end Powerglide with no problems at all. Since it's a two-speed transmission, however, it's not desirable for street use. The TH350 is a good choice for both street and race applications, but is limited to what it can handle. With a small budget you can get one to handle 450 hp. If higher hp capacity is required, it can be very costly. That said, the TH400 is the best all around because with just a few upgrades it can handle high-hp applications and still be very streetable."
Achilles Thomas: "The Powerglide is very old trans and should only used for drag racing applications in vehicles that are more concerned with track times than fuel economy. It can also get very expensive when built for high-horsepower drag racing applications. As for the TH350, it is great for small-block applications, very cost effective and reliable, and there are plenty of affordable aftermarket parts for it. The TH400 is one of, if not the strongest transmission to ever come from GM. It's great for racing applications, heavy-duty trucks, and big-blocks with lots of torque. You can find these units built at a fair price depending on their expected use. The 700-R4 is our most popular transmission due to the streetability offered by its four speeds. It's easy to swap into older cars that come with Powerglides, TH350s, and TH400s. Likewise, it offers great fuel economy and performance. There really isn't a downside to this transmission."
Zack Farah: "Balance in shift firmness is primarily a matter of personal preference. Smoother shifts are comfortable and produce very little shock to the drivetrain; a daily driver would benefit such an application. Firm shifts reduce clutch pack wear, but transmit greater shock loads to the drivetrain, U-joints, axle splines, and body mounts. It's all a balancing act based upon the car's intended use, and the durability of the rest of the drivetrain."