GMC with 478 V-6
 

Pretty cool V-6. In the comments, he claims14-15 mpg

Re: GMC with 478 V-6
 

Fantastic Upgrade!

Re: GMC with 478 V-6
 

I doubt that very much. My dad had a 68 GMC with the 351. We were very lucky to get 10

Re: GMC with 478 V-6
 

My 66 with the 305 V6 got 12 MPG - uphill, downhill, empty, loaded, towing, it didn't matter.

Re: GMC with 478 V-6
 

I agree. When in tune, these big V6's are incredible. A large displacement engine that puts out over 400 lbs of torque starting at 1200 rpms in a light tonnage vehicle can do wonders with a high speed rear end ratio. This engine will pull like a team Belgian drays just above idle.

Re: GMC with 478 V-6
 

Judging by the paint on the exhaust manifolds I'd say that thing has no miles on it to know the mpg

Re: GMC with 478 V-6
 

Just to be clear, I doubt the mileage claim - it probably burns that much just idling.

But it is definitely a cool engine. I loved my GMC V6.

Re: GMC with 478 V-6
 

I showed a YouTube of a GMC 2500 with a 478, I think in Heavy Haulers. I bet it's the same truck

Re: GMC with 478 V-6
 

My '62 GMC 6500 with a 478 got roughly 7 to 9.

My '66 GMC Pick-Up with a 305 got a surprising 15 1/2 Hi-way after a super tune.

I too have my doubts on 14 to 15 for a 478.

Re: GMC with 478 V-6
 

Yep K, same truck. I saw a different YT video that I lifted the engine pic from. Looked up his mileage comment

Re: GMC with 478 V-6
 

If it is the same truck, it's a Green truck with a Blue interior.

Re: GMC with 478 V-6
 

I've seen a red one with a 401. This guy here also has a BWA 5500 tanker w/478

Re: GMC with 478 V-6
 

I like to give him the benefit of the doubt. How many others have done this swap? This vehicle is not a big rig loaded up to 30K GVW or 65K GCW combination, which is what this engine is designed to be used in. Maximum economy is when manifold vacuum is high. Vacuum is highest when you foot is not heavily into the gas pedal. With this much torque at low rpm's, your foot doesn't need to be into it. Easily handle a 3.54 or higher ratio.

Re: GMC with 478 V-6
 

*Old Man Alert* The only complaint I have about what he did is that the exhaust was too loud! :lol:

Re: GMC with 478 V-6
 

I love the hum of a 6cyl. This one has a nice deep tone. I think it sounds pretty mellow considering he's running it out. We don't know what he has for sound proofing. Probably has the Dynamat or similar

Re: GMC with 478 V-6
 

All the V-6's have a unique sound to them. My 478 had Dual Straight thru Mufflers that ended a little passed the cab. Like a Detroit, that's music, lol.

Re: GMC with 478 V-6
 

This is true. I always heard the GMC V6s liked the gas as much as a V8 and this is a big V6 engine. But making the required torque at low RPM with a light touch on the throttle equals less fuel consumption. It takes less to get 'er movin'. Also he has a Gear Vendors.

I had two 3/4t 4wd '72s. One had a 350/TH350, 4.10 gears, and 33" tires. The other had a 400SBC/4spd, 4.10 gears, and 35" tires. They both got 12.5 mpg. The torque of the 400 took very little throttle to run the truck and the taller tires helped at the top end