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How To Improve MPG & Performance With An Overdrive Transmission - CHP How It Works

Going Broke Filling Up Your Hot Rod? Here’s How to Improve MPG and Performance With an Overdrive Trans

Stephen Kim Jun 15, 2011
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GM automatic transmissions quite literally rule the world. The venerable Powerglide has been the gold standard of durability and efficiency in drag racing since the ’50s, and the workhorse TH400 has been factory installed in everything from big-block Chevelles to Ferraris to military-spec Hummers. In the hot rodding world, GM automatics are routinely swapped into Fords and Mopars, but you’ll hardly ever find a C6 or a TorqueFlite in a Chevy. The reason for this is two-fold. First off, GM simply builds kickass transmissions. Secondly, what GM does better than any other manufacturer on earth is stick with a small handful of trans models, keep them in production for decades, and continually enhance their durability along the way. This yields an economy of scales that drives down costs, and ensures parts compatibility for both factory and aftermarket components for decades. The only downside to this is that there are so many great transmissions to choose from that several GM transmissions will work great for any given application.


Fortunately, that’s a great problem to have, and the solution is usually quite simple. In the wake of gas prices that have once again eclipsed the obscene mark, our focus this month is on GM overdrive automatics. To help distinguish between the pros and cons of each of GM’s overdrives—in terms of cost, durability, weight, size, and efficiency—we sought the expertise of the best trans builders in the business. They include Stan Poff of TCI Automotive, Achilles Thomas of Monster Performance, and Zack Farah of Gearstar Performance Transmissions. We also consulted with Rick Johnson of Gear Vendors to explore the benefits of a more nonconventional approach to overdrive performance.

Overdrive Advantage

Zack Farah: You can usually expect a 30 percent savings in fuel consumption with an overdrive transmission due to three primary factors. First off, most GM overdrives have a Fourth gear ratio of 0.70:1. Let’s say you have a car with a 3.73:1 ring-and-pinion ratio and 27-inch diameter rear tires. With a TH350 or a TH400, your car would be turning about 3,000 rpm at 70 mph. On the other hand, that 3,000 rpm multiplied by an overdrive ratio of 0.70:1 yields a cruise rpm of 2,100. That’s a reduction of 900 rpm. Another factor to consider is that popular overdrives like the 200-4R and 700-R4 are low-inertia transmissions. They require less torque and horsepower to spin them up, compared to a TH350 or a TH400. Less parasitic drag equals more power to the rear wheels. Lastly, the 200-4R and 700-R4 have lower First gear ratios than the TH350 and TH400. The First gear ratios on the 200-4R and 700-R4 are 2.74:1 and 3.06:1, respectively. In comparison, a TH400 has a 2.48:1 First gear ratio and the 350 has a 2.52:1 ratio. Therefore, the overdrive transmissions offer a lower overall First gear ratio, which translates to better off-the-line performance and better fuel economy since they don’t load the motor as much when getting the car moving from a stop.


Stan Poff: Overdrive transmissions substantially lower cruise rpm. With gas as expensive as it is these days, that translates to increased fuel mileage and savings at the pump. With an overdrive unit, cruise rpm on the freeway is typically reduced between 25-33 percent. This can easily equate to a 3- to 5-mpg improvement and make for a much more pleasant cruise as well. Most hot rods have free-flowing exhausts, so a vehicle will be much quieter when turning 1,500-1,800 rpm on the freeway with an overdrive versus 3,000-3,500 rpm without one.

Selection Process

Zack Farah: GM has made so many great overdrive transmissions over the years that it can be challenging to pick the right one for your car. That said, there are some important differences between them to remember to help with the selection process. With the advent of the 700-R4 and 200-4R in the early ’80s, technology had not yet evolved enough at the time to enable us to manufacture our transmissions into what they are today. In the ’70s and ’80s, the TH350 and TH400 were the only choices for high performance since they had been around for many years and the aftermarket technology had fully developed. By the ’90s, however, the 700-R4 and 200-4R had proven themselves to be durable units when the right parts and manufacturing techniques were employed. Our 200-4Rs can handle 800 hp. Today we see 4L80Es being built to withstand three times the horsepower and torque over the factory’s original ratings. Moreover, the stock 6L80E, being the newest and most technologically advanced of the GM transmissions, has limited high-performance capabilities. The 6L80E and 6L90E, with proper modifications and high-performance upgrades, can handle higher amounts of horsepower over stock, but they still haven’t caught up to the TH400 and 4L80E. The 6L80 is controlled by its own internal computer, and therefore, it is very challenging to install into anything other than its original application. Gearstar Performance and HGM Performance are in the final stage of development for a stand-alone computer controller of the 6L80E.


Achilles Thomas: Of all the GM transmissions Monster offers—like the 200-4R, 700-R4, 4L60E, 4L80E—there is a lot of overlap among different models. For instance, both the 4L60E and 4L80E would be suitable for a 500hp street/strip machine. That said there are many options when trying to select the best overdrive trans for your car. The first step in the selection process is determining your current transmission model. Let’s say you have a ’70 Chevelle that has a TH350 with a 9-inch tailhousing, and you will be dropping in a beefed-up 383ci small-block with 500 hp. Furthermore, you are looking for some better top end and improved fuel economy while staying on a tight budget. For a street/strip application like this, the best choice would be our Monster 700-R4 SS package. It would be the same length as the TH350, has awesome top end gearing, and requires no computer so it offers the most bang for the buck. If the plans called for running some nitrous and you really wanted to gear it toward track use, another option would be the 4L80E, which is virtually bulletproof. There are literally hundreds of different variables, and our staff is always glad to help you through the selection process.


Total Cost Involved Trans Lineup

Stan Poff: Several things separate TCI’s Street Rodder, Street Fighter, and Super Street Fighter lines of transmissions. These transmissions feature specific shift characteristics and horsepower capacities to suit a wide range of applications. The Street Rodder transmission is capable of handling 475-525 hp and shifts slightly firmer than a stock transmission. Our Street Fighter transmissions are rated at 525-725 hp with firmer shifts than the Street Rodder. The additional horsepower capacity comes from clutch and band upgrades as well as increased fluid pressure and flow. TCI’s Super Street Fighter transmission is the next step up and can handle 825-1,025 hp depending on the specific model. It has the best of everything internally, and is just one step away from being a competition transmission with a full-manual valvebody.

NonElectronic Overdrives

Zack Farah: Both the 200-4R and 700-R4 are excellent choices for those who want to upgrade to an overdrive without having to deal with electronics. In some applications a 200-4R is the better fit, as its dimensions are more slender, while other applications are better suited for the more durable 700-R4. In a car like an early Nova, a 200-4R would fit better than a 700-R4. Both transmissions operate with hydraulic logic via a throttle pressure cable to mechanically measure the throttle position from the carburetor to the transmission control valvebody assembly. This controls the shift timing, shift quality, and line pressure rise. There are no electronics involved, and converter lockup is controlled by a 12V wire that energizes the lockup solenoid once a vehicle reaches highway cruising speed.


Stan Poff: The 700-R4 and 200-4R are popular swap candidates because they offer the benefits of an overdrive transmission without the hassle of electronics. Both transmissions can be built to handle more than double what GM designed for them from the factory. The 200-4R transmission is an easy replacement for the TH350. To upgrade from a TH350 to a 200-4R, all that’s required is changing the shifter. Most of the time, even the original driveshaft can be retained. With fewer replacement parts made for the 200-4R, when it comes to horsepower capacity, the upper hand goes to the 700-R4. TCI has developed a constant pressure valvebody for both of these transmissions. This innovation eliminates the problematic TV cable gremlin. With this valvebody the cable is now mainly used to set the shifting speed and no longer controls the pressure. It’s still important to get the shift speeds correct, but at least destroying the transmission is less likely.

Achilles Thomas: The 700-R4 and 200-4R are both extremely popular units for overdrive conversion, and each has their benefits. Regarding durability, the 200-4R was never put into a high-horsepower or heavy-duty truck application and was often found in midsize cars. On the other hand, the 700-R4 was pretty much used in everything from a V-6 Camaro to a fullsize truck. That being said, right from the factory the 700-R4 was deemed to be more durable, and now in today’s market, there is a vast amount of aftermarket upgrades available for the 700-R4 that make it the favored choice for overdrive conversions. In regards to price, the 700-R4 and 200-4R models that Monster Transmission carries are very similar, typically within $100-$200.

In terms of size, the 700-R4 is just over 30 inches in length from front to back, and the 200-4R is about 3 inches shorter at 2711/16 inches from front to back. So if you were converting from a TH350 with a 9-inch tailhousing, the 700-R4 would be a direct swap with no change in driveshaft length. A TH350 with a 6-inch tailhousing would be an easy swap for the 200-4R, again with no driveshaft mods required. In terms of weight differences, a typical 700-R4 weighs in the neighborhood of 135 pounds versus roughly 125 pounds for the 200-4R. These weights can vary depending on fluid capacity. An aftermarket heavy-duty aluminum pan will obviously add some weight in comparison to the factory steel pan.

Turnkey Conversion Packages

Achilles Thomas: The easiest way to upgrade to an overdrive transmission without having to worry about running a computer would be to go with a Monster 700-R4 overdrive conversion package. Our 700-R4 packages are turnkey solutions that are mechanically operated, which means no complicated electronics or expensive computers are required. These packages include everything needed for an overdrive swap along with detailed instructions and toll-free tech support to walk you through the process. Another option is the 200-4R, which we also offer as part of a complete conversion package. Monster’s conversion packages include either a 700-R4 or a 200-4R trans, a performance torque converter, a dipstick, a throttle cable, coolant line fittings, converter bolts, a trans mount, speedometer gears and housing, an external lockup kit, a trans cooler, and a dust cover. There are a couple of optional items as well, such as a crossmember and driveshaft and in some cases you can actually reuse those parts. If not, we offer a full line of custom crossmembers and driveshafts to fit your application. When you purchase from Monster Transmission you never have to worry about hunting around for additional parts or pieces. We make it easy.

Trans Controllers

Stan Poff: Running an electronically controlled transmission in an older muscle car has always been a challenge. The 4L60E and 4L80E can now be used in older-model vehicles or as replacements in newer vehicles thanks to TCI’s EZ TCU. The TCU controls the electronic functions of these transmissions, and doesn’t require a computer or laptop to load the programming onto the trans. The EZ TCU has a handheld scanner that asks some basic questions, such as the tire size and gear ratio being used, and follows a basic program menu to get the car up and shifting rather easily. The basic EZ TCU program will work for 90 percent of the customers, but if they wish to fine-tune it a little to better suit their tastes, the customer can go back in the scanner program and raise shift points and make speedometer adjustments as well. For those computer geeks out there wishing to have more control over their transmission tuning, there is the standard TCI TCU that lets you control many more parameters.

Trans Evolution

Zack Farah: The 4L60E, the 4L65E, and the 4L70E are essentially the same transmission based off the 700-R4. The difference is that they’re electronically controlled, and each successive variant features increased torque capacity. The 4L60E was introduced in 1993 and configured to LT engines; the 4L65E was introduced in 1999 and configured to LS-style engines. In 2005, the 4L65E was re-designated the 4L70E and designed with more durable internal components. The choice of one over another is dictated by a vehicle’s horsepower and torque. Gearstar can manufacture all GM electronic transmissions beyond their factory horsepower and torque capacities. Stan Poff: GM transmissions are always being updated, and 700-R4 and 4L60E have come a long way. Not too long ago, 600 hp was really pushing the limits of these transmissions, but now they can handle 800-plus horsepower. This enhanced durability is attributable to stronger drums and input shafts made from special materials, along with billet servos, billet pump rotors, and higher performance frictions, steels, and bands. Likewise, the TCI’s EZ TCU also addresses and manages line pressure issues as well as pulse modulations in the converter. This allows for automatic lockup, thus cutting down on early wear.

Achilles Thomas: The 4L60E is an evolution of the 700-R4, while the 4L80E is an evolution of the TH400. The 700-R4 and 4L60E are pretty much identical in every way, including their size and horsepower capacity. If a novice were to put the two right next to each other, they would have a hard time telling the difference between them. On the other hand, the 4L80E looks quite different from the TH400. It is usually 3-4 inches longer and slightly heavier, but the durability between the two is about the same. We can build either a TH400 or a 4L80E to easily handle over 1,000 hp. The main advantage of the 4L80 is that is has a 0.75:1 overdrive ratio. Needless to say the 4L80E and TH400 are extremely durable.

Six-Speed Options

Stan Poff: The 6L80E came from the factory with GM’s torque management programming built into the vehicle’s electronics, which manipulates engine tuning to reduce

torque output in an effort to increase transmission longevity. That alone should give you a good idea as to the problems it faces. I personally know GM Proving Ground engineers who have tried to step up the performance of vehicles equipped with the 6L80E, and they haven’t been very successful. TCI has been analyzing and planning some upgrades for the 6L80E in order to make it live behind added horsepower. To the contrary, the 4L80E was a very good transmission from the factory. Like most all of the transmissions coming from GM, there are always upgrades made during their manufacturing runs that make each transmission a little better, hence the 4L85E has been improved over the 4L80E with stronger planetaries and improved oiling circuitry. Some refer to the 4L80E as the TH400 with an overdrive ratio, as much of the internals are interchangeable. TCI has a complete line of 4L80E transmissions in the Street Fighter and Super Street Fighter trim levels. These are better constructed with many aftermarket components that will allow it to handle much more horsepower and increase durability for even normal daily driven vehicles.

For a best-of-both-worlds solution, TCI developed the 6x Six Speed transmission, which was born out of the 4L80E. To accomplish this, TCI manufactured proprietary components, made fluid circuitry changes, and engineered two more gears into the transmission. The TCI 6x Six Speed transmission features ratios of 2.97:1, 2.23:1, 1.57:1, 1.18:1, 1.00:1, and 0.75:1. In addition to shifting through all six gears on its own with the gear selector in the “OD”, the 6x Six Speed can also be shifted manually with paddle shifter or a two-button shifter with hard wires by installing a toggle switch that allows the controller to go back and forth from automatic mode to manual mode. This trans is a real workhorse, and current models consistently endure 850-1,000 hp with ease. Furthermore, TCI has developed better components and upgrades expected to take it to the 1,500hp range shortly. It also uses modular bellhousings, so it can be easily adapted to many application offered by GM, Ford, and Chrysler.

Factory Overdrive Alternative

Rick Johnson: A Gear Vendors overdrive unit is a supplemental planetary assembly that bolts to the output shaft of the transmission in place of the tailshaft housing. It features a 0.78:1 ratio for a 22 percent reduction in cruise rpm, essentially converting a two- or three-speed trans to an overdrive trans. So if your car turns 3,500 rpm on the freeway, it will lower rpm by nearly 800. Gear Vendors overdrive units are available for Powerglide, TH350, and TH400 transmissions. In most GM applications, installing a Gear Vendors unit requires little to no modification to the trans tunnel at all. The factory crossmember can be retained, and the only other change necessary is shortening the driveshaft by 121/2 inches. The big advantage of running a Gear Vendors unit on an earlier two- or three-speed GM trans is that the older transmissions are stronger, more reliable, easier to repair, and have less parasitic loss than factory overdrives. They also eliminate the need for electronics and lockup converters. Not only are Gear Vendors units great for improving fuel mileage, but they can handle 2,000-plus horsepower in racing applications. Once a Gear Vendors unit has been installed, it is engaged with a shift button that’s usually mounted on the shifter. Once you click the button for overdrive, a green light on the dash lets you know it has been engaged. Simple electronics that come with the kit shut off the overdrive when you come up to a stop or reach low speeds. The electronics also give you an AutoDrive and AutoLaunch features, which are cool for cruising or racing.” CHP


Gearstar Performance Transmissions
Akron, 44308
TCI Automotive
Ashland, MS 38603
Gear Vendors
El Cajon, CA 92020
Monster Transmission
Brooksville, FL 34601



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