Stall Converters and the TBSS

One of the cheapest ways to cut your ET is by installing a replacement torque "stall" converter. The stock converter stalls at around 1900 RPM's which is far short of the TBSS torque curve. The recommended stall for a TBSS is in the 3000 -3600 range.

The "average" gain in the 1/4 mile is about .5 seconds off your ET when adding a quality race converter.

I personally started with a Yank PTB3200 stall converter which has a stall speed of 3200 RPM and retains full towing capacity. This converter is good for about .3 savings at the strip.

After a trans failure I decided to switch to a Vigilante 3600 and give up the ability to tow. The Vig stalls higher and is generally a looser converter. The only reason I switched to Vigilante is because they offer a triple disc clutch that they claim can be locked at wide open throttle which is something Yank does not offer or recommend.

After testing the Yank 3600 converter against the Vig 3600, the Yank was became the clear winner for performance. It was tighter for better drivability yet still stalled the same.

I think the 3600 is the ideal performance stall for the AWD Trailblazer SS. Someone with a 2WD TBSS might consider less stall in an effort to keep from braking the tires loose.

Few things to note with stalls on the TBSS.

  • When you use a stall converter of any size (usually 26-2800 or higher) you will lose your speedometer when you go wide open throttle from a dead stop until you let off. If you are already rolling the speedo will work as normal and if you only go partial throttle it will work. But WOT from a dead stop will cause the speedo to stay at zero until you let off.
  • Most stall converters will kill your ability to tow. Check with the stall manufacturer about its capabilities
  • Your truck will naturally be louder than stock. So you might consider making exhaust changes after you settle on your stall. This is because the truck might be revving on average 1200 to 1500 RPMs more getting up to speed. So more motor/exhaust noise.

Stall Speed
True stall speed can best be determined using a transbrake. But for all practical purposes you can test brake stall by stepping on the brake and start accelerating the motor to the point the brakes will no loner hold the truck then this is the stall speed.

Flash Stall is usually a little higher than rated stall speed. This is the maximum RPM you see when you launch at full throttle.

Loose/Tight converter
You may have heard it said that a certain converter is looser than another. This has nothing to do with the actual stall speed as you can have a loose converter and a tight converter that both stall at 3000 RPM.

So even though a converter is rated to stall at a certain RPM at full throttle, it starts engaging and moving the truck forward at a much lower speed. A "tight" converter takes less throttle to get the truck moving and a "loose" converter takes a lot more throttle to get it moving.

Finally, a tight converter drives much more like factory than a loose one. My Yank converter would not slip much under 50% throttle so you really did not know it had a stall. Well until you went over 50% throttle :)

Sizing (picking your stall)
It is common practice to order a converter with a stall speed that is 500 to 750 RPM lower than the peak torque of your vehicle.

STR (from Yanks website)
Stall Torque Ratio is one of the most misunderstood aspects of torque converter construction. Our competitors often call stall torque ratio: torque multiplier. The stall torque ratio is the amount of engine torque that the torque converter can multiply at a particular rpm level. By definition, stall torque ratio is when the turbine is at 0 RPM's and the converter is at maximum designed stall. This will produce a positive push on the turbine to increase the torque to the input shaft of the transmission, multiplied by the designed stall torque ratio of the torque converter. For example, a stall torque ratio of 2.0 would multiply 200 lb. ft. of engine torque to 400 lb. ft. of torque at the transmission input-shaft.

The misconception of stall torque ratio is that more must be better. This is not always the case. High stall torque ratio applications, typically are for industrial equipment or engines with limited low rpm engine torque. With high stall toque ratio converters, there are important trade-offs. What you take at one end you give up on the other. Typically, a torque converter with a very high stall torque ratio, such as 2.0-2.5, will be much less efficient above its rated stall speed. There is a sacrifice in higher rpm efficiency to achieve high stall torque ratios. That lower efficiency translates into less horsepower transmitted to the tires over an RPM range.

The problem with a high stall torque ratio converter is that it is only high while the car is not moving. Maximum stall torque ratio occurs at wide open throttle with no rotation of the transmission input shaft. As the input shaft starts to rotate with vehicle forward movement, the stall torque ratio will become non-existent much sooner than a converter of the same stall, with a lower stall torque ratio. A converter with a stall torque ratio of 2.2 for example, would display that at the starting line, but it would drop off much sooner than a converter with a lower stall torque ratio. See graph:

Transmission Coolers
Any "slip" in the transmission including the converter will cause additional heat. Because the the higher stall converters are slipping more they are creating significant heat. Heat is the #1 most common failure for transmissions. Consider purchasing a quality cooler if you plan on running a stall. Actually, consider a cooler even if you are not. PCM of NC offers what is un disputably the nicest TBSS cooler on the market with plug and play lines. more info

 

 

Shootout Links Yank Converters Vigilante Converters PCM of NC cooler
 

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