Big Block V6: 1968 GMC 2500 Truck

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Pat L. found this 1968 GMC 3/4 ton pickup for sale in Menifee, California. Upon first glance, it looks like a well used long wheel base pickup and it certainly is. But what powers this truck is an interesting engine that has a cult following among GMC owners. GMC equipped their light duty and heavy duty trucks with a big block V6 engine of various displacements from 1959 to 1974. This truck is equipped with a 351 cubic inch V6 engine. It has been listed here on Craigslist for $7,900 for about a week.

The GMC big block V6 engine was a 60 degree engine built in both gasoline and diesel versions. Both V8 and V12 derivatives were also produced based on the V6. The V6 engines came in multiple displacements with the most common being the 305 cubic inch V6 that was used in 1/2 ton pickups from 1960 to 1974. I own a 1966 GMC pickup that was the 305E version big block V6 engine that was rated at 165 horsepower and 280 lb ft of torque. It is a terrific engine with lots of low end torque. GMC also built 351, 401 and 478 cubic inch displacements. The subject 3/4 ton pickup has the larger 351 cubic inch V6 engine. The E series of this engine was used from 1966-1969 in light and medium duty trucks.

The interior of this truck looks better than the exterior. The seat has a JC Whitney seat cover and the dash pad is cracked. An aftermarket gauge package has been mounted under the dash. The seller states that they have had the truck for 10 years and was used for many years by a missionary traveling from California to Mexico. The power steering on the truck has been upgraded to a modern unit. The front brakes have also been upgraded from drum to disc.

One improvement that most GMC owners make is to replace the factory 2 barrel carburetor with a Holley 2300 carburetor that pulls in 500 cfm of air. This carburetor is pretty much bullet proof and improves the power and drive-ability of a GMC V6 truck. This upgrade was made by the seller along with dual exhausts. While the body is rusty, the heart of this truck is strong and would make a great driver while considering a cosmetic restoration.

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  1. alphasudMember

    I finally see a 68 GMC with the V6. I think that’s the only year you could get the V6 in this body style. Yea, it’s a little too rusty for me but for the fact it’s still running and driving is a testament to how well built this driveline is. I’m in the middle of a 64 GMC project for a customer and that one is going to get a Holly Sniper kit. I will probably need an adapter for the intake manifold but other than that should run well. The gas engine is basically built like the diesel. Super HD and the engine weight is around 900# so no lightweight casting for sure. Spark plugs are in the V of the engine which is cool. Would be cool to find a 401 but those are just about nonexistent now and we’re used in the medium duty line.

    Like 3
    • Cooter914 Cooter914Member

      Actually Alphasud, the v6 was offered all the way through this body style. By 69 I think the only Chevy motors allowed were the 350 and 396. Everything else was a GMC motor. Gotta have that brand identity ya know. Lol

      Like 5
      • Andy

        Unless you’re in Canada. The V6 was only available in heavy-duty trucks. GMC trucks buolt here back then are essentially rebadged Chevrolets.

        Like 3
  2. gbvette62

    These 68-72 GM trucks were some of the nicest looking trucks ever made. I always thought the four lamp grill of the GMC was always just a little better looking than the Chevy.

    My first high school summer job was delivering plumbing pipe hangers and supports for high rise and commercial buildings, to job sites. The truck I used was a 350 4bbl powered, orange 69 3/4 ton Chevy Longhorne. I really liked that Chevy, it was a good truck. I’m sure this GMC is a good truck too.

    Comparing this truck, with it’s manual trans and rubber mat interior, to my 21 Denali, it’s just amazing how much trucks have changed in 50 years. This GMC was your typical truck at that time, right down to the step bumper, now you can’t even buy one with a manual trans.

    Like 5
    • Tom Lyons

      GMC used Pontiac engines in the 50 ,s v 6 was used as early as 63 , may be even earlier , they definitely have a distinct sound

      Like 1
  3. pwtiger

    I’ve seen the internals of these V6 engines, the connecting rods have to be a foot long and stout. Lots of low end torque good for towing, not good for fuel mileage.

    Like 6
  4. Tom Lyons

    Big block term should not be used for these motors

    Like 0
    • steve

      Yeah, I see what you mean. Weighs 860 lbs. Chevy 454 weighs 761. Both are toys compared to a REAL big block like a 6-71 Detroit at 2195 lbs. My bad….

      Like 1
  5. Carnut

    What a great deal for someone, I own a Chevy C10 shortbox and can attest these are fantastic drivers. For home depot runs can’t be beat – mine has a strong 350 and three pedals and can burn out anytime anywhere. When I consider my neighbor bought a Denali Ultimate in Jan. for $100k and it sits in his driveway I find these to be the deal of the Century!

    Like 0
  6. George Birth

    Durable Work truck

    Like 2
  7. JCH841

    I learned to drive a manual in our dad’s maroon 69 GMC 1500 with the 305 V6 and three on the tree. As stated, the V6’s has torque with a capital T. Unfortunately, my younger brother learned to roll over trucks in it.

    Like 2

    Built when GMC trucks were actually better in some ways than their Chevy
    brethren, nowadays a GMC is a Chevy with less letters in the name plate.

    Like 2
  9. steve

    That engine was the standard school bus offering for many years. It would run for years in the “foot to the floor” stop and go that most buses were subject to. I recall the TV ad where the police car was chasing the bad guy and broke down. The officers (Yes, two per car!) flag down the GMC pickup to have him give chase, They said “I sure hope this is a V8!” and were crestfallen when the driver said it was a 6. “Oh, don’t worry, just hang on!” and off they went and caught up to the “villain” is short order. The ad only ran a short time. It was odd to even see that commercial because GMC really didn’t sell many trucks to “retail” customers. They were all business accounts in the 60’s

    Like 1
  10. Tom Lyons

    Big block term was used when the 396 was introduced, was only really used in mid sixties to Chevrolet’s, there was confusion in 71 with a 400 small block and a 402 big block in the full size cars because the both had 400 emblems on the fenders

    Like 1
  11. Mike

    And now it lives in Ohio..

    Like 0

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