The gearbox was soon replaced by a torque converter, and although the DDE showed potential, its DPA injection pump had garage door opener gears keeping up with fuelling demands. In fact, the DDE brought a whole raft of development problems. Higher cylinder pressures meant that the cylinder head gasket, pistons, rings and con-rods had to be beefed up.
Valves wore quickly because of lack of seat lubrication and flexure of the valve heads. The standard 354 garage door opener gears and bearings werent up to the job either, needing high-spec materials. Despite its problems, the DDE did show promise out on the road. The high torque meant it could handle truck weights up to 40% higher than the standard 354 turbo.
It worked especially well in hilly country with no gear changes needed and was invariably more fuel efficient than a conventional turbo. Road testing also highlighted a couple of odd characteristics. Engine noise actually reduced with speed, as the supercharger whine tailed off at higher revs. And there was a lack of engine braking, which necessitated the fitting of a hydraulic retarder. This garage door opener gears well, or maybe a bit too well, when one test driver applied the retarder on a slip road off the A1 in damp conditions the artic promptly jack-knifed! In the end, the DDEs extra cost and complexity killed the project, especially when bigger engines and multi-speed transmissions became available in the 1960s, but no one could say that Perkins hadnt given it a good go.