TCI Transmission and Torque Converter Technology Insights - CHP Insider
From the February, 2009 issue of Chevy High Performance
By Stephen Kim
Photography by Stephen Kim
Stan Poff of TCI
Those who insist on rowing their own gears just might be insecure in their manhood. If you're into sacrificing big wads of e.t. in order to feel extra tough, you probably have issues-the main one being chronic dragstrip defeats. Real racers run automatics, but unfortunately, the road to straight-line heroism is often littered with expensive driveline shrapnel. For some expert advice on how to extract maximum performance and longevity from trannys and torque converters, we had a chat with Stan Poff of TCI Automotive. Since transmissions fail as often as celebrities enter rehab, and few components affect e.t. as profoundly as a properly matched torque converter, it's advice worth listening to.
Most hot rodders know that a tranny cooler is something they should install, but many just haven't made the time to do so. Unfortunately, such a casual attitude may not be the right approach. "In any place other than Antarctica, you should install a transmission fluid cooler," opines Stan. "Anytime you separate the cooling of the transmission fluid from the radiator, where the temperature can run over 210 degrees, you will promote longer transmission life. Instead of the transmission fluid only being cooled to the temperature of the radiator coolant, it will now run about 20-30 degrees cooler than the engine by using a separate transmission cooler."
While stall speed represents where in an engine's powerband a converter will flash, it doesn't indicate how much the converter will multiply torque. A converter multiplies engine torque at a 2- to 3:1 ratio (known as the multiplication ratio), so stall speed isn't the only thing you should pay attention to. "Multiplication ratios can vary from one converter to the next, depending on a converter's internal component makeup," says Stan. "For example, we can build three torque converters that have the same stall speed, but different multiplication ratios simply because of the different combination of stators, fins, and clearances used in each unit."
Stall speed is a measurement of how high a converter will flash in a specific application due to engine torque and load. The "flash" point, simply put, is the rpm at which a car moves from a dead stop under full load. The torque converter's diameter, fin angles, internal parts clearances, and stator design are some factors that determine stall speed. Matching stall speed to a given application is critical for optimum performance, but the advertised stall speed of a torque converter is just a ballpark figure. "Stall speed varies depending on the load placed upon the converter from the engine and the vehicle weight," explains Stan. "If you have two vehicles with identical motors and rear gear ratios, and the only difference between them is vehicle weight, the same converter will stall more in the heavier car, because it sees more load. Likewise, if you have two identical vehicles with the exception that one produces an extra 100 lb-ft of torque, the vehicle with more torque will flash its converter 200 or 300 rpm higher, so this should all be taken into consideration when choosing a converter.
Since improper installation procedures can make expensive new hardware go kaput, here are some tips on how to avoid them. "The most common mistake we see is not flushing the transmission fluid out of the factory radiator cooler or an aftermarket cooler before installing a new transmission or converter," explains Stan. He also suggests thoroughly flushing out the torque converter when installing a new transmission. This prevents contamination that can lead to rapid parts failure. Furthermore, Stan recommends setting the converter-to-flexplate spacing at 1/8 inch. "With all the variances in engine blocks and transmission cases, this measurement may not be perfect for every application, but it will get you in the ballpark," Stan says.
There's more to choosing the right torque converter than stall speed and multiplication ratio. The entire vehicle package needs to be taken into account. "In order to recommend the correct converter for your application, we need to know vehicle weight, engine displacement, cam specs, carburetor size, cylinder head and intake manifold specs, rearend gearing, tire size, and whether or not you're running a power adder," says Stan. "Dyno figures are always a plus, but the key is providing us with thorough information so we can make the proper recommendation."
"Black has always been the best color to dissipate heat out of an engine or transmission, but it was hard to identify TCI converters from those of our competitors, since they also painted their units black," Stan says. "We tested many different colors to try to find something that dissipated heat as well as black, which would distinguish our product line from the rest. Eventually, we ran upon a coating that is gunmetal gray, with metal particles mixed in it. It proved to be better than any of the blacks we tested by running 10 degrees cooler and dissipating heat more quickly. Now called HDT coating, it is applied in a different environment from a typical paint booth, but it was well worth the investment."
"TCI Automotive's method of testing transmissions is a three-step process. First we check the valvebodies by subjecting them to a 200-plus-psi hydraulic test to make sure they operate as designed. Next we use a transmission hydraulic tester. It bolts onto the transmission in place of the valvebody, and the transmission is then subjected to fluid-line pressure to ensure it seals properly in all gears. Finally, the valvebody is bolted onto the transmission and the entire transmission assembly is tested on our new ATS Electronic Dynamometer. The dyno utilizes a 40hp electric motor and a software program written specifically for each type of transmission we manufacture. The dyno measures the horsepower and torque going into and coming out of the transmission in each gear to make sure they're within an acceptable range."
Automatic transmissions are incredibly complex, but the efforts taken to ensure longer life in big-horsepower applications encompass four key components: the pump, the planetary gearset, the valvebody, and the drums. The pump supplies all the oil into the converter and throughout the transmission. This fluid pressure is critical, as it keeps clutches and bands applied in each gear under load. The planetary gearset multiplies engine torque and, when designed properly, reduces stress on other internal parts in the transmission. The valvebody is responsible for supplying transmission-line pressure and selects the gear the trans operates in. The drums house the clutch and steel combinations, which carry the load in certain gears. "Factory clutch combinations were meant for factory vehicles," explains Stan. "TCI uses modified combinations and friction materials in these clutch packs to allow more horsepower to run through the transmission. We have transmissions that survive in 3,000hp applications, which is possibly due to the rugged composition of our clutch and steel combinations."
"SFI is a foundation that conducts independent testing of parts that can cause damage to a race car, race car driver, or surrounding spectators if they fail," Stan says. "TCI has to submit products to the SFI Foundation and meet their testing standards before we can sell them to consumers. Transmission shields, flexplate shields, flexplates, and balancers are some of the products that must be submitted for SFI approval. SFI testing on shields involves spinning a drum or flexplate until it explodes, then making sure the shield adequately contains the debris. Flexplates must spin at a certain rpm for a certain period of time without failing before they can pass the SFI test. In addition to parts costs, TCI must pay the SFI Foundation for each test it conducts. Once TCI parts pass the test, we then have a standard to build our products by."
Choosing the right transmission for your car is often a trade-off between durability and power consumption. Fortunately, GM has offered a wide variety of transmissions over the years, and the Powerglide, the TH350, and the TH400 are among the most popular. According to Stan, in a heavy-load, high-horsepower application, the TH400 would be the best choice, but he also points out that there are lots of hard parts available for the TH350 that would allow using it in similar applications. "In classes like NHRA Stock and Super Stock, a TH350 might be a better choice than a TH400, because it takes less horsepower to operate," says Stan. So where does that leave the venerable Powerglide? "Three-speed transmissions are usually better in vehicles weighing more than 3,000 pounds, but the Powerglide is usually better in vehicles lighter than 3,000 pounds, since they use about half of the horsepower compared with a TH350," Stan says. "The Powerglide also yields a lower starting-line gear ratio, allowing small-tire cars to leave the gate without frying the tires."
While very few people are daring enough to tackle rebuilding an automatic transmission themselves, TCI offers complete rebuild kits to get the job done. More importantly, TCI has some sound advice to help avert disaster. "The first thing I would recommend would be to have a transmission manual on the type of transmission you are attempting to rebuild," suggests Stan. Although TCI's kits come with instructions, they explain where the parts go, not the actual process of how to perform the rebuild. "I would also suggest one or two classes in a college vocational program," Stan says. "I've taken four during my time at TCI, just to learn the basics of transmissions and how they work, and our tech guys have all taken one or two courses. It's a necessary evil."
In mega-horsepower race cars, rubber engine and trans mounts won't cut it. Using solid mounts all around may seem like an easy solution, but TCI warns against doing so. "Solid motor mounts are OK, but TCI recommends using rubber or polyurethane mounts on the transmission," suggests Stan. "You want a mount that will absorb some of the shock the drivetrain will experience from hard shifts and chassis twist, as well as possible misalignment of the transmission in the vehicle. Solid transmission mounts/trans misalignment is the number-one cause of case breakage around the bellhousing in TH350s, TH400s, and Powerglides."
Loose converters are great for launching hard out of the hole, but slippage simply wastes power at the far end of the track. While older GM converters don't incorporate lockup mechanisms, they can still be tightened up near the end of a quarter-mile pass to improve trap speed by 1 or 2 mph. "In order to accomplish this, you need to tighten up the clearance between the turbine and the pump assemblies to 0.060-0.080 inch," explains Stan. "TCI's standard turbine clearance is around 0.080 inch, although in some NHRA Super Stock and Comp Eliminator cars we have run as little as 0.040 inch to reduce slippage at the far end of the track. When you run such tight clearances, the alignment of the input shaft to stator support is critical, and the distance from the converter case and pump to the engine block should be kept to a minimum."
Options are often limited for late-model racers looking to beef up their trannys, so many ditch their six-speeds and 4L60Es for old-school slushboxes. However, there are some things to look out for to avoid headaches, and dimensions and fit are the primary concerns. "You can bolt a TH400 to the back of an LS1, but the stock converter configuration won't work," explains Stan. "TCI has designed converters for the TH350 and the TH400 that will bolt directly onto late-model applications. Other things to look out for are tunnel space, speedometer hookup, passing-gear hookup, linkage compatibility, and errors from the PCM, since it's no longer receiving a transmission signal."