Curbside Classic: 1963 GMC Pickup – The Very Model Of A Modern V6 Truck Engine

(first posted 6/30/2012)   It’s beginning to sound like a broken record, but the years 1960-1961 were undoubtedly GM’s most creative and adventuresome ever: rear-engine Corvair; aluminum V8, the Tempest with half-a-V8 four and swing axles, the Buick 90° (three-quarters-V8) V6, Greenbrier van and Rampside Corvair. And there was another: the GMC truck V6 engine, which appeared in 1960. And unlike the Buick V6, this was a proper one indeed: 60 degree cylinder angle for even firing pulses, and a compact block assuring a short and stiff crankshaft. It was quite the bombshell; never mind its V12 “twin-six” version (post here). 

Why a V6? Good question. To be different, for its own sake? Possibly, but not likely. And why not a V8? Hmm. Let’s look at the historical context, and perhaps a good answer will formulate.

GMC was famous for their truck in-line sixes; well, actually, that’s all they ever built, as gas engines. It was a venerable line, starting in 1939, when GMC stopped using the Pontiac six. The primary family included displacements that varied from 228 inch³ to the legendary 302.

270 inch GMC sixes powered the legendary “Deuce and a half” Jimmy 6×6 military trucks and other equipment in WW2, of which some 800k were built. Take that! We drove one and posted that here, with video.

These rugged ohv engines also were popular with the hot rod set in the late forties and early fifties, because of their big cubes (270 and 302), overhead valves and ultra-tough construction.

There was  also a “large-block” GMC inline six, with 426 and 503 cubic inches, for the really big rigs and buses.

Given that a six cylinder intrinsically has a torque advantage over a comparable-sized V8 (all other things being equal), staying with that proven number of cylinders makes gobs of torque sense, for true truck engines. There’s a reason why literally every semi on the road has a six under its big hood.

And it was the era for GM to feel modern, so why not go all out and design the very model of a modern six? The 60 degree cylinder angle is of course the preferred one, since it affords an even firing interval of 120 degrees if a split journal crankshaft is used, as had been the case since Lancia’s V6 since 1950. In cross-section, it looks somewhat similar to the little Chevy 60º V6, eh? Well, the block is a bit deeper and beefier.

The GMC V6 was designed for serious truck duty, and came in a range of displacements from 305 inches³ to 478 inches³. Oddly, there was even a V8 version with 637 cubic inches, with twin balance shafts to compensate for its uneven-firing and vibrations, due to its odd 60° block. They were all relatively low-rpm engines, with some versions producing their maximum power below 3000 rpm.  The M “Magnum” series that appeared in the mid-sixties had bigger ports and valves, and less constricted exhaust headers, and are the most powerful and desirable of the family.

I drove a GMC V6-powered medium truck, for an interstate sign erector outfit, and its characteristics were distinctive, in relation to the other trucks in the fleet. Its low-end torque put the typical Chevy small-block to shame, and was palpably better than the Ford FE-powered ones. It bit hard right from idle, and its characteristic sound was of course unique. We’re used to the slightly-tense grumble from the Chevy 60° V6, and the GMC V6 shared some of that, but through a megaphone. At full chat through some shorty pipes, it was memorable; more so than its actual power output, which was hum-drum.

It was America’s love for big V8s in their pickups that killed the GMC V6 in that role. As GMC started offering more Chevy V8 power, the V6 was relegated to entry-level duty, and eventually disappeared. In truck applications, it soldiered along until 1978, eventually also replaced by the growing appetite for diesels, or the big-block Chevy V8, which was undoubtedly cheaper to build.

The GMC V6 was also built in a diesel version, the Toro-Flow, as a cheaper alternative to the “Million-miler” Detroit Diesel 6-71. Probably the less said, the better. It had a spotty reputation, and I doubt anyone ever racked up a million miles on one. Many were eventually replaced with gas V6s or something else.

Some folks did put them in their GMC pickup trucks, like this one installed in 1967 in a then-new GMC pickup. They did better in less-demanding applications.

The gas 305 was the standard engine for pickups, and most likely is what thrums under the hood of this fine old veteran. Rated at some 135 or 140 hp, this was designed to be a blend of six-cylinder economy and V8 power, although some early complaints had those qualities switched around.

Which may help explain the mystery of the Scotch plaid valve covers some of these engines had. This picture is from the web site, which offers two alternative theories as to why a number of these motors sported them. What did I say about GM feeling adventuresome?

This particular truck first caught my eye when we moved here in 1993, sitting a couple of blocks down the street from us. It’s right up my alley, as you undoubtedly know by now. And it’s obviously got a granny-low fours speed, with a stick a yard long. Plenty of elbow torque to make sure it gets into the next gear.

This one sports a “Custom Cab”, the Brougham version of upgrade in the still-spartan early sixties. Mainly chrome, on the grille, bumpers and some trim. And that luxurious color-keyed arm-rest, on the interior. It was the way to distinguish a hard-core work truck from a soft-core work truck.

What really makes this truck exceptional is its original aluminum canopy. It and the truck have weathered the decades so gently.

That also explains the non-rotted out boards in the bed. Have they ever felt sunshine or rain? Maybe not.

The manufacturer’s plate is still there, and I had to do a double take when I first read it. I assumed there was another name ahead of MFG. INC, as in NIEDERMEYER MFG. INC. What was it, and why was it missing? Then I realized it was “GEM MFG”. Duh! A long-time maker of high quality pickup toppers. And from Portland too, which confirms this to be a “native”.

Always wished my truck had a nice big bumper like this. They were optional; trucks back then came without rear bumpers unless you wanted one. And this is the one to want.


Our walk-around is at an end. This truck went up for sale shortly after I shot it, and naturally, I was tempted. But what was I going to do with another old truck? A young guy bought it, and I saw it in another part of town for a while, and then it disappeared, for good. Hopefully, it’s being kept in a way so it will be around for another fifty years. It deserves it.

Related article on the GMC V-12 engine.