Diesels are great engines for tow vehicles. They twist out enough torque to get any load moving without the bad fuel-gulping habits of a big-block engine. But when you ask them for some compression braking to slow you down on a steep grade, they can't hold a spark plug to a gas engine. Now you know why diesel trucks come with such big service brakes!
The reason diesels run away from you on hills is simple: Gasoline engines have throttles that close when you lift your foot from the accelerator pedal. Diesels don't. Sure, you can take your foot off the accelerator pedal in a diesel truck and that will limit the fuel supply to the engine but it does nothing to limit the amount of air being sucked into and pushed out of the engine. In a gasoline engine the closed throttle plate causes a massive restriction that the pistons have to try to suck air past. This restriction causes drag in the engine that slows the truck. For all intents and purposes diesels have an unrestricted air supply at all times, so in order to produce engine drag the exhaust brake was developed.
Knowing that many of you own diesels (or want to) and experience diesel engine runaway, we wanted to see first-hand how well an exhaust brake upgrade works. We borrowed Off Road Unlimited's F-250 and drove out to Azusa, California, to follow along as Banks Engineering installed its Banks Brake and SmartLock transmission controller. Typically it takes five hours for Banks to install this system on a Super Duty, but plan on a day if your truck is lifted like ORU's. With the system installed we experienced a drastic improvement in engine braking whenever we turned it on. When the Banks Brake closes its restrictor valve there is a distinct but muted whoosh sound accompanied by a tremendous amount of engine braking (more than any gasoline engine could produce). The system is designed to work seamlessly with the rest of the truck and will disengage the brake when vehicle speed is less than 15 mph or engine speed drops lower than 1,600 rpm. Banks reports that some drivers will leave the system on at all times, and that doing so has no ill effects on the system or truck.
For more information on the Banks Brake (systems for Cummins and Duramax engines are also available) or any Banks product check out www.bankspower.com. The gas truck guys already admire your diesel's pulling power; now Banks will make them beg for its braking power too.