Vintage Truck of the Day: 1947 Mack LTSW – New “Western” Truck With 300 HP Hall-Scott 400 Gas/Butane Engine – “The Most Powerful Truck Engine Built!”

This as was paid for by Hall-Scott, to bring attention to the fact that the new Mack LT “Western” truck series, targeted for those grueling jobs on the far side of the continent was available with the legendary H-S 400 engine, a 1091 cubic inch six cylinder monster with an aluminum OHC hemi head and able to crank out power that no diesel could hope to match back then (typically between 115 and 165 hp).

This was quite a change for Mack, as it was a fully integrated East Coast truck maker that built all the major components that went in them, including engines, transmissions and rear axles/bogies. That had to change to meet the demands of West Coast operations, which involved much larger loads, off-road logging, and of course mountains. The Hall Scott delivered the massive low-rpm torque and maximum power needed for those conditions, at a price: massive fuel consumption. One operator got 1.7 mpg hauling heavy over-the road loads.

Here’s a shot of a restored first year 1947 LT:

This one is H-S powered, and wows the crowds with its exhaust sound at truck shows.

And here’s a gathering of several different vintages. Cummins diesels as well as Mack’s own were also available.

An over-the road LT semi hauling a trailer with descriptive company name.

Update: butane is petroleum gas, a byproduct of natural gas and oil refining. It’s used in a number of ways, as a feed stock for further refining, and as a fuel for stoves, lighters, etc.  It has an octane rating of 92, and has long been used to increase the octane of regular gasoline to create premium gasoline. It makes an excellent motor fuel, superior to propane due to its higher octane, which is why the H-S engine produced more power on butane than gasoline, with a concomitant increase in compression ratio, from 5.7:1 to 7.1:1.

Here’s an SAE article on butane as a motor fuel

More detailed info on the Hall Scott 400 Invader engine here