A TRUE Jacobs Engine break works in conjunction with the exhaust valves. There are 12 volt solenoids that when the clutch is fully engaged and the trottle is at idle this completes a loop circuit and the exhaust valves does not fully open, creating a extreme amount of back pressure. I've driven trucks with this option since the early 70's. A exhaust break is basically a gatevalve that closes off the exhaust creating a lot of pressure on turbo and so on. With a electric "Jake Break" you can have on a Cummins a low, med, and hi, because of three individual heads. On Caterpillar engines in general you have a low, and hi because of two heads. Don't know of anything available for a gas engines.