There’s a reason this 1950 GMC truck has such a swollen hood: It’s covering up a giant Detroit Diesel 6-110 engine, designed primarily for marine, military, industrial and railroad use. Although not originally intended as a highway truck engine, it was installed in three prototype 1950 GMC trucks, one of which was leased to Pacific Intermountain Express to gain experience with it in regular use. With their raised and elongated hoods and correspondingly higher cab, they were certainly formidable looking, and with 275 hp they would have offered direct competition to the similarly-powerful Hall-Scott 400 series gas truck engine.
But no further units were built, as there were a couple of issues, which were deadly in this application.
The 6-110 was created in response to the need for greater power that didn’t require lashing together two or more 6-71s, for high-power demands in marine, military and industrial settings. It arrived in 1946, and like other DD engines, its number referred to the 110 cubic inches per cylinder, for a total of 660 cubic inches. In principle, it was essentially a scaled-up 6-71, and shared certain key components like the unit injectors, governor and marine reduction gears.
There was one big (and fatal) difference: instead of using the tried and proven Roots type blower as used on all the other DD engines, GM decided to use a centrifugal blower, located right above the flywheel.
Here’s a rare surviving example of a 6-110 with that type of blower. From a knowledgeable comment left at a forum post:
The original 6-110’s were produced with a rear mounted centrifugal blower, which was driven at a 13:0.1 over-driven ratio which was fine for constant rpm applications, or as used in Budd RDC’s (Rail Diesel Car) where they were governed at a maximum of just 1,600 to 1,800 rpm and no chance of over-speed above 2100 rpm (crank speed). As used in mining / haul trucks and governed at 2100 rpm…. they would not tolerate ANY amount of over-speed conditions without the compressor turbine in the centrifugal blower disintegrating and sending fragments into the engine.
Furthermore, the blower drive gear and shaft were undersized, and failed commonly, especially in situations where the engine speed varied often, as would be the case in a highway truck. GM tried reducing the blower ratio to 11.0:1, but that did not create enough draft to properly evacuate the two-stroke cylinders and led to smoking.
Here’s a few blurbs from the time.
These issues were not as fatal in other applications that saw more continuous duty. The 6-110 found favor in marine use as well as in powering the Budd RDC self-propelled rail cars, as seen above, which used two of the 275 hp units per car. The centrifugal blower is quite visible, on the far end of the block. These RDC engines each fed a torque converter, which allowed shiftless speed up to 85 mph. The RDC was a rare success in its field, allowing railroads to downscale their shrinking passenger operations prior to the creation of Amtrak. A number of them are still in service.
In around 1951, the 6-110 block was redesigned to use the tried-and-true Roots blower, as seen here in this one being run up. In this case, the blower is exceptionally noisy, because its air intake is wide open, without any air cleaners and their plumbing.
Presumably the Roots blower version would have been much better suited to over-the-road trucks, but apparently the experiment of installing the 6-110 in trucks was deemed unsuccessful in other ways too, and not taken up again.
As a frame of reference, here’s what a production heavy duty GMC diesel truck looked like at the time. It came with either the 4-71 Detroit Diesel “Jimmy” as in this truck above with five bars in the grille, or the 6-71 inline six was rated at 165 hp in 1950, which was on the high end in terms of powerful diesels of the time (six bars in the grille). GM steadily raised the power of the 6-71 in the 1950s, until it reached 238 hp, and eventually 285 hp when it was turbocharged.
What really killed the 6-110 was the arrival of the larger V versions of the -71 family arrived, with the 8V-71 offering 318 hp and up to 360 hp when turbocharged, and of course the even larger 12V-71, never mind the V16 and V24 versions. The 6-110 did continue on until 1965, and with turbocharging eventually made some 350-360 hp. Its production ended in 1965.
The 110 was essentially replaced in 1967 by the 149 Series engines, made in V8, V12 and V20 configurations. These were typically used in mining, marine, generation and other related applications. They were built until 1999, and their power was steadily increased through improvements in their turbocharging and electronic engine management systems (DDEC). The final version of the 20V149 made 2,936 hp (in standby generator use) from its 2,980 cubic inches, an impressive feat for a large diesel.
I’d like to imagine this PIE truck duking it out with a Hall-Scott gas engine truck on a long grade somewhere out West.