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Automatic Transmission Performance Upgrades: Shift Kits, Valve Bodies, and Tips

First, the cheap tips:

  • Most newer transmissions have automatic safeguards to prevent you from destroying the transmission by accident. They will upshift and downshift even when you manually select a specific gear (don't try this with a real three-speed TorqueFlite!) as the engine speed nears the redline or the stalling level. This means that you can get maximum engine performance by selecting first gear...we don't recommend this as an everyday practice and are not responsible for any damage that occurs if you try it.
  • Replacing the transmission fluid with Mopar Type 7176 can increase the life of your transmission, while eliminating some shifting problems. We recommend retraining the computer after changing the fluid. Click here for details and four-speed automatic quick fixes.

Why manual transmissions provide better economy and performance

There was a time when professionals actually raced with automatic transmissions and could beat the manual-transmission crowd. Back in the 1960s and 1970s, the Chrysler TorqueFlite was very efficient, but manual transmissions could be balky and hard to use. Using a high-torque engine like a 440 or Hemi meant that you could afford to lose the tiny amount of power given up by the TorqueFlite in exchange for faster, more consistent shifts. But times have changed. Modern transmissions are designed for more comfortable, smooth shifts, and often upshift prematurely (even under full throttle). Shifts tend to be slower. Meanwhile, manual transmissions have come a long, long way. It is easy now to shift quickly and efficiently with a clutch, and five or six speed transmissions maximize power.

Automatic transmissions lose power because they have a fluid interface: the pass power along through a thick oil. Lockup torque converters improve highway economy, but must be disengaged while upshifting. Manual transmissions have minimal power loss because they rely on two plates pressing tightly against each other.

In short, it is normal for manual-transmission versions of the same car to outspeed their automatic-transmission brethren by about one second from zero to sixty, while getting three to six miles per gallon better mileage. The cheapest performance upgrade you can make is to buy your next car with a five-speed, because it costs less and gives more.

Shift kits and valve body converters

Okay, so you already have a car with an automatic, or want one which only comes with a "slushbox" (so named because the engine's power has to travel through "slush," or, more accurately, oil). What can you do? Most people do not want to retrofit their car with a manual, or can't. Hence the shift kit for better shifts, and the manual valve body for "manumatics." Or, as Ean Orsel wrote...

  • Manual Valve Body: Turns your auto tranny into a partial-manual tranny.
  • Shift Kit: Makes your auto tranny do the exact same thing it does now, but better.

(There does not appear to be a manual valve body for the four-speed electronic automatic used by current Chrysler, Dodge, and Plymouth front-wheel-drive vehicles, since it does not have a valve body as such, according to Damien Civiello.)

Shift kits

Steve Knickerbocker wrote that "Smooth shifting transmissions accomplish [smoother shifting] by being in two gears at once when shifting up. It's known as shift overlap. Shift kits reduce or eliminate the shift overlap and speed up actuation of the shift, hence the harder feel to the shift. A shift kit will reduce wear because you won't have the trans trying to be in two gears at once."

Ross Bond wrote: "A firm shift is best for the transmission, the biggest problem with the 604, is the clutches are slipped so much between shifts, which gives you a very smooth shift, but makes lots of heat and wears out the seals and clutches a lot faster. Also 1994 and older cars are running on software in the controller which is bad for the transmission. They have what is called EMCC, this means an electrically modulated convertor clutch, which partially locks up the torque convertor to reduce slippage and fuel economy loss in the lower gears, but think about the heat that the convertor clutch is making when it is partially applied. Which in turn kills the seals in the transmission. Some controllers are flashable and some are not. You can update to the newer ones in an older vehicle." ... "you can tell if the controller is flashable by looking at it. It is usually on the pass fenderwell. If it has cooling fins on the side of it, it is flashable. "

There appears to be a shift kit for the A-604/Ultradrive transmission, which seems to be based on replacing or upgrading the current computer. Damien Civillo wrote:

As I understood the shift kit it was similar to one for a standard transmission in that it replaced/modified some of the parts in the stock valve body so that the fluid flow is different. In other words, since the valves monitor/control fluid flow in the valvebody (the valves are electronic rather then hydraulic) this kit changed the way fluid flows through the valve body so that it modifies the input signals and tricks the tranny into behaving differently. Sort of like the boost bleed switches that some people rig up. We're just tricking the tranny into thinking that something else is happening when it's not.

Manual valve bodies

Manual valve bodies replace the automatic transmission's valve bodies with a manually controlled one. It is similar to using an AutoStick or Tiptronic except that it does not automatically upshift or downshift if you forget. These are for the truly dedicated. Ean Orsel wrote that with the shift kit for the A-413 three-speed automatic...

The stock gears, as indicated are PRND21 from front to back. The shift kit makes it PRN123 from front to back, and putting it in 3rd makes the tranny go into 3rd. Unlike 'Drive' starts in 1st, and climbs "Automatically" to 3rd. Whatever gear you pick, it goes there and stays, like a manual.

Jeff Chojnacki noted that faster shifts are better for automatics and slower shifts are better for manuals, and to Ean Orsel's message about shift kits:

[there is no automatic upshift] Except in 1st gear. 1st will neutralize when you take your foot of the gas. Also it will neutralize if you shift into 1st gear at high speed. Kind of a safety feature.

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