FB Performance Has A SECRET WEAPON
Secret Automatic Weapon Exposed
A number of years ago a device was developed and patented by FB Performance Transmission in New York. Known as the “VSC” or Variable Stall Control, it has quietly been affecting the way many savvy Racers are now launching and racing their cars more effectively. Yes, many have been quiet about it because they realize that they have a big edge over their competition. That edge comes in the form of a double-edged sword: Because not only is the vehicle’s launch improved, but the entire run is positively affected due to the greatly improved coupling efficiency of the torque converter.
Many racing automatics such as the Powerglide, Turbo400 and AO3 transmissions can incorporate this unique device. The VSC was originally developed for the typical Turbo-charged application where previously the only way to build boost rapidly and launch with some effectiveness was to use a “loose” or high stall torque converter. This worked good to some degree to get the car out of the hole, but as the engine develops full boost the increase in torque is also very dramatic. So much so that this loose converter just can’t couple properly and will slip during an entire pass. This slippage is immediately converted to heat. So when you add the trans fluid temperatures created during a typical launch while using a trans-brake (50 degrees/second) to a converter that’s slipping that much (30 to 40 degrees/sec), its not uncommon to find that the steel input shaft has been heated to such a degree that its changed color. Of course within a short period of time the repeated over-heating and cooling will only impact a transmission’s internal components in a negative way.
The VSC, Variable Stall Control system is designed to permit a “tight” lower stalled torque converter to suddenly become looser (increase stall rpm) with the same amount of initial engine torque. It accomplishes this by uniquely allowing a portion of the pressurized fluid in the converter to discharge back into the pan. When this occurs there’s an immediate increase in the stall rpm of the converter which typically averages to about 1000 rpm. A really nice feature is that this window of increased stall rpm can be turned off at any desired point thereby offering some tune-ablity.
So now when the VSC is used in any application (like Turbo,
Supercharged, or Nitrous) the engine is capable of reaching its launch rpm just
as rapidly as it would with a high stall torque converter. The really neat thing is that once the VSC is
turned off, the converter recovers to its original stall setting causing it to
couple much more aggressively and efficiently.
A typical example is a racer with a 1900 hp 632 ci., 2-stage Nitrous
engine in a 3,200 lb car. He was able to achieve some remarkable (but
not uncommon) results after adding the VSC and tightening the 4500 stall
converter by 1000 rpm. Previous data
logs showed that although the car was getting a 1.19 sec. 60 foot and running
7.98 at 171mph in the ¼ mi. the converter was slipping about 10% going through
the traps. The later data logs with the
VSC in operation showed only 1.2% converter slippage. It’s not surprising then that the car went
7.47 @ 182 mph. This is after gaining coupling
efficiency of nearly 9% of the engine’s 1900hp which had been previously lost
and converted to just heat.