Turbocharging the 354 for a projected 150bhp looked like a quick and easy solution, but the reality proved more complex. Testing in marine, industrial and farming applications threw up no serious problems, but hard-worked trucks proved to be a tougher environment. The 354 turbo exposed weaknesses in the cylinder block, crankshaft, pistons/rings, cylinder head and its gasket, all of which had to be strengthened to garage door opener goes up but not down with the extra power.
Perkins would fit test engines to fully loaded trucks and drive them round the clock to see what would garage door opener goes up but not down next, but eventually the turbo six turned into a reliable power unit. But that wasnt the end of 354 developments. In 1970 an intercooled version was launched, rated at 155bhp at 2600rpm. Claimed to be the first ever vehicle engine with a standard air-to-air intercooler, it was aimed at trucks up to 24 tonnes GVW. The media was duly impressed by its responsiveness, and the first production lorry to use it was the Dennis DB24T.
A more radical variation on the 354, though one that never reached production, was the DDE Differential Diesel Engine of the early 1960s. This was supercharged, but with a twist. Instead of increasing boost as revs rose, the blower boosted power at low revs, the aim being the power characteristics of a DC electric motor, with a torque curve as close to horizontal as possible. Originally invented by Dr P W Glamann, who worked on the same idea for Berliet, the Perkins prototype added an epicyclic differential between the engine and a torque garage door opener goes up but not down The diff drove the supercharger, and was arranged to increase boost at lower revs.