Do you think it might be a bypass system - they used to be common and called "cut-outs" in a pre-1920 car. They operated by a flapper valve in the exhaust to cut out the tail pipe and muffler and vent straight to air to give extra power when hill climbing. Wouldn't want to live on a steep hill with streams of open cut-out cars plodding past at 1,000 decibels!
I doubt they would be exhaust cutouts. Why bother cutting holes in the bonnet and running pipes? The few exhaust cutouts I have seen, simply open the exhaust to air under the vehicle. More common than cut-outs were exhaust whistles but they would not be what is shown on the truck. As the name suggests, they diverted the exhaust through a whistle. The whistle sounded as each cylinder exhausted! They were extremely loud. No doubt they were very popular with any hoons who could afford a car in the 1920's or earlier.
I have my shoulder to the wheel,
my nose to the grindstone,
I've put my best foot forward,
I've put my back into it,
I'm gritting my teeth,
This photo is an excellent quality black & white 8” x 10” borderless new photo reproduction of a 1930s BM MACK with an Integral Sleeper operated by SAFEWAY TRUCK LINES, Chicago, Ill. The original photo was taken in Chicago in 1949. It is a most fascinating photo of a road worn long lived Mack, still on the road after many, many years! This is a BM Mack with real character!!
DESCRIPTION: #88 in the SAFEWAY fleet, this old Mack carries a 1949 Illinois license plate. Some 3,030 BM Model Macks were produced between 1932-1941. Most were gasoline powered, but this road horse has been repowered with a Cummins Diesel, as evidenced by the “Cummins Power” metal badge on the front hood side. While it has a vertical exhaust stack with a thin muffler, it also has 4-straight pipes coming up out of the right side of the hood through neatly cut holes, indicating that it was a Cummins 4-banger.
This Mack is parked on a residential city street, with a late 1930s automobile behind it. With a 1949 plate, this weary Mack must have been at least 8 years old, and probably much older. Most likely it saw service right through WWII when few parts were available, and probably had many modifications made. Arrow-style turn signals have been added, mounted on a reinforced patch on the battered front fenders that are torn from many road miles of vibration. This tractor has a hinged windshield with a single wiper, a left-side mounted spotlight, small rectangular side-view mirrors, a single air horn mounted in the center of the roof, 2 extra headlights mounted under the front bumper, fabricated angled ‘eves’ over the small integral sleeper cab side windows, old style saddle tanks, and extra reflectors mounted on the front of the fenders. Talk about “character”, this old Mack has it! If this weary old Mack could only talk, I’m sure it would have many a fascinating story to tell!
SAFEWAY TRUCK LINES, INC. Little is known about Safeway, except they were located at one time at 4625 W. 55th Street, Chicago 32, Illinois, just east of Chicago Midway Airport. Photos of some other Safeway trucks appear on the internet from 1961 and 1969.