I hate to sound critical, but low compression DOES equal low power. Also lots of smoke and low efficency (and therefore more fuel consumption). Raising the boost is simply taking an inefficient engine and stuffing more air in it, raising the effective compression ratio to what it would be if the engine were designed properly.

Durability is more a case of proper design than compression ratio -- MB uses hardened cranks and substantial bearings, for instance, along with a pretty advanced oil filtration system. If and engine runs high boost without problems, but dies if it has 21:1 compression rather than 18:1, I'd say the basic design is poor -- and GM is famous for inadequate design, especially in diesels. If running at 21:1 destroys the bearings, the design wasn't stressed properly.

My Volvo is designed to 23:1, and usually has more like 26:1 in most new engines, and they run 300,000 miles in automotive use, not bad. Makes good power for its size (104 hp on 2.4L) -- boost is about 13 psi, I think. Huge bearings, though......and oil cooled pistons, etc.

American diesel practice has been, up to 1994 or so, to make constant speed, stationary engines, circa 1940, and stuff them in trucks and tractors. No real changes in 50 years -- low compression (for a diesel, they won't even run without external heat under 16:1), very long stroke on small cylinders, direct injection, and fixed injection timing, with a usable rpm range of about 1800 to 2200 rpm.

There have been exceptions (Mack, for instance, uses high compression -- 30 to one in some cases), but the Germans have been out front on this for a very long time.

Short stroke, high compression, variable injection timing, indirect injection engines produce considerably more horsepower and torque over a much wider (1000 to 5500 rpm) range with better fuel consumption and far less smoke -- take a look at any modern diesel, particularly the new Volvo and Cummins big truck engines.

After all, over the road trucks in the US had draft tubes for blowby until the early 90s......pitiful.

Even the new pickup engines are seriously low on power by MB standards -- my 603 puts out about the same horsepower and 50% more torque that a Chevy Vortec by displacement.....and that's a gas engine!

Oh, and the theoretical max boost from a single stage turbocharger is about 20 psi -- no way you can get 30, sorry, unless you have either an axial compressor or a two-stage centrifical compressor.

I think the record for boost probably still stands, though -- Napier made a diesel aircraft engine in 1953 -- called the Nomad, that had a 12 cylinder horizontally opposed design, 1200 ci displacement, with a coupled 8-stage axial compressor/3 stage axial turbine. The last and greatest of the turbocompound engines, produced 3700 hp and 400 lbs static thrust.

Needless to say, at 12:1 compression ratio, it was almost impossible to start, and at 8 atm (118 psi) boost I don't know how they kept the heads on. No one ever bought it, and when Rolls Royce bought Napier out, they discarded the diesel, added three feet to the "turbo" shaft along with some combustion chambers and made the RR Avon turbojet out of it!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!