The early GM ½ tons roll along relatively well on today’s highways considering the roads they were designed for 50 to 60 years ago. As highways became better Chevrolet and GMC added extra horse power six cylinder engines (each model had its own inline six cylinder) to satisfy the demands of many buyers.
Even with this improvement the ½ tons could still not keep up with the higher speed limits on the open road. American ingenuity comes to the rescue! In recent years many owners that love their early GM ½ ton pickup and want no major changes, have develop methods to overcome this lower speed handicap. Just when enthusiast think they know why your ½ ton rolls along with traffic, they become shocked when they see what looks like an all original drive train. They thought it had a small block V-8 but appears to be a ½ ton just like it came from the factory! The following describes one method to create a ½ ton that is a pleasure to drive for the enthusiast.
Enter Bill Miles of Ashland, Massachusetts with a near show quality 1953 GMC ½ ton. He really enjoyed driving his pickup however, on even the flat flat smooth highways he was held back in the slow lane. He thought “there must be (maybe a combination of things) that can increase speed and less the engine RPM”.
Here was Bill’s formula to increase speed, reduce engine RPM’s, and make even many experts say “I cannot believe what I am seeing”.
DIFFERENTIAL:
He replaced his original 4.11 ratio ring and pinion for the recently introduced 3.55 ratio. All is hidden inside the differential housing. This alone gives almost a 20% increase in extra top end speed.
TIRES AND WHEELS:
Bill removed his aftermarket 15” 6 bolt wheels. Their radial tires were 27” in diameter.
He went back to the original GM 16” wheels that increased the size to 30.5. The tires added were 215/85 R 16 radials. This 3.5” increase in diameter made a noticeable difference!
In fact, Bill states the improvement with the differential gearing and tire diameter increase dropped the RPM 800 at 65 mph.
SIX CYLINDER ENGINE EXCHANGE:
For the maximum speed increase using the factory “big brother” engine in place of the standard ½ ton engine was the adding the larger six cylinders used by GM on the 2 tons, cab-over-engine bodies, and most school buses. Most use almost the same overhaul gaskets, so they are almost identical in appearance.
CHEVROLET: The engine of choice is the 261 cubic inch full oil pressure in line six. It will really wake up your early GM ½ ton! See our very detailed article on this engine on our website tech article series at https://oldchevytrucks.com/.
GMC: The 228, 248 and small port 270 original GMC six cylinders are good solid engines but when you really get serious on extra horse power it is the 302 that is on the top of the list. GMC even use a 2 barrel carb to get the most from these extra cubic inches. It also was in the 2 ton, cab-over-engine and school bus from about 1956 to 1959.
For Bill Miles, his 1953 GMC ½ ton has become a pleasure to drive. He has driven through the USA on vacation about 40,000 miles in the last 15 years. It is a nice cruiser at 65mph. Yes, once he tried it at 80 mph but he noticed strange body sounds occurring so he decided to keep it at its best speed of 65 to 70 mph!
