GMC with 478 V-6 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**72 tigger** · 08-06-2022, 02:00 PM

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

**MusicMan70** · 08-06-2022, 02:35 PM

Fantastic Upgrade!

**kwmech** · 08-06-2022, 03:04 PM

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

**truckster** · 08-06-2022, 03:52 PM

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

factorystock · 08-06-2022, 09:06 PM

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.

**special-K** · 08-08-2022, 12:10 PM

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

**truckster** · 08-08-2022, 03:49 PM

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.

**special-K** · 08-08-2022, 03:58 PM

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

1968 GMC CM2500 w/478 V-6 driving. - YouTube

C10 - C90 Bill · 08-08-2022, 04:32 PM

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.

**72 tigger** · 08-08-2022, 05:34 PM

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

C10 - C90 Bill · 08-08-2022, 06:03 PM

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

**special-K** · 08-09-2022, 09:38 AM

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

1963 GMC BWA5500 w/478 v-6 - YouTube

factorystock · 08-09-2022, 08:47 PM

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.

**Steeveedee** · 08-09-2022, 09:08 PM

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

**special-K** · 08-10-2022, 07:46 AM

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

C10 - C90 Bill · 08-10-2022, 08:57 AM

Quote:

Originally Posted by special-K

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

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.

**special-K** · 08-12-2022, 06:58 AM

Quote:

Originally Posted by factorystock

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.

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

08-06-2022, 02:00 PM	#1
72 tigger Senior Member Join Date: Apr 2008 Location: Berne IN Posts: 3,203	GMC with 478 V-6 Pretty cool V-6. In the comments, he claims14-15 mpg Attached Images __________________ 71 C10 72 K20 72 K10 Super Kirk

08-06-2022, 02:35 PM	#2
MusicMan70 Senior Member Join Date: Feb 2011 Location: Corona, CA Posts: 1,820	Re: GMC with 478 V-6 Fantastic Upgrade! __________________ MusicMan70 1961 GMC Suburban

08-06-2022, 03:04 PM	#3
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,387	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

08-06-2022, 03:52 PM	#4
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,791	Re: GMC with 478 V-6 My 66 with the 305 V6 got 12 MPG - uphill, downhill, empty, loaded, towing, it didn't matter. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

08-06-2022, 09:06 PM	#5
factorystock Registered User Join Date: Feb 2007 Location: west coast Posts: 3,351	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.

08-08-2022, 12:10 PM	#6
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	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 __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

08-08-2022, 03:49 PM	#7
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,791	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. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

08-08-2022, 04:32 PM	#9
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,064	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. __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

08-08-2022, 05:34 PM	#10
72 tigger Senior Member Join Date: Apr 2008 Location: Berne IN Posts: 3,203	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 Attached Images __________________ 71 C10 72 K20 72 K10 Super Kirk

08-08-2022, 06:03 PM	#11
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,064	Re: GMC with 478 V-6 If it is the same truck, it's a Green truck with a Blue interior. __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

08-09-2022, 08:47 PM	#13
factorystock Registered User Join Date: Feb 2007 Location: west coast Posts: 3,351	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. Attached Images

08-09-2022, 09:08 PM	#14
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,081	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! __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

08-10-2022, 07:46 AM	#15
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	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 __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~



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