Why Can’t the 47RE Hold More Power?
The main reason the Dodge heavy-duty four-speed automatics don’t do well with more power is their low hydraulic line pressure, which actuates the bands in the transmission. This pressure problem can be solved, though, by the installation of a performance valve body or shift kit, a pan-off upgrade that involves removal of the valve body and installation of new internal components to increase pressure and improve shift firmness. That’s exactly what Power Driven Diesel and PowerTech Diesel did to Fisk’s truck.
“The problem with most shift kits is they do not allow much more than a 25 to 30 percent increase in line pressure, which equates to a similar 25 to 30 percent increase in power-holding capacity at the transmission itself, but just a small 10 to 15 percent increase in power holding capacity at the torque converter lockup clutch assembly,” explained Terry from Power Driven Diesel. “Performance valve bodies can raise the line pressure even more, but there are several internal transmission components that should be upgraded from factory cast to billet aftermarket parts when line pressure exceeds 50 percent over stock levels.”
A stock 47RE will only safely handle 100psi of fluid pressure, while a Racing Valve body from Power Driven Diesel can handle 225 to 250psi, and thus more than 1,200 horsepower output.