It looks like a GMC 6-71 blower. These hung on the side of an inline, two-stroke "Jimmy Diesel", later known as a "Detroit Diesel", or "DeeTroit".
The engine was ubiquitous. Busses, trucks, construction equipment, military, marine, industrial. And then there was the blower--after duty on one of the above, the 6-71 found a home on almost every engine you can think of. Vaporizing M&H Racemaster slicks, pushing past the 200 mph barrier in drag racing, faster still at Bonneville, blowing the sides of blocks and entire bottom ends out of engines of all kinds, and inspiring giggles and peed pants in school boys everywhere as streetrods of every kind waved the 6-71 flag a foot tall out of the hood or polished to a mirror shine in a hoodless fenderless rod.
Smaller versions, and larger, and different series such as the 8v-71 and 14v-71s soldier on today. The design is also copied by B&M and others.
Air in the small side, air out the big side. As installed on the Detroit or Jimmy engine, the blower is bolted to the side of the block and blows into the cylinders via "lights" or holes through the block into the cylinder which are opened and closed as the piston travels up and down.
Like so--the top engine. You can click on the pic for a closer look:
As installed on V8's in sits on a blower manifold between the two cylinder banks. A fine installation here and no, you're not seeing double--well you are, sort of...
Other installations include direct crank drive in front of the engine with the charge going into a manifold via tubes. You can find that set up about half way down here, along with many other variations.
On the 5th pic down, you'll notice a "lip" on the side of the case(bottom of pic). That denotes a INLINE 6-71 application. The lip helps holds the blower on the side of the motor til you get the bolts in. There is also a 6V71 version that doesn't have that lip.
Here is my galaxie getting one installed on it.
My case has the lip still on it, though it's on the other side. Usually most guys cut the lip off, but it doesn't interfere with my install.
These motors were very popular boat motors, also large gensets. Anything that had a constant rpm, as these motors had a narrow powerband.
Ah yes have one of these sitting the boat, Grey MArine 6-71 Two-storke Diesel, and as they say every stroke is a power stroke. The one in the boat is a side mount also.
I was told the was a lo-boy and Tall-boy model 6-71, never seen anything that proved it, just something that was muttered by some who-dats at morning coffee.
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