Heavy hauler mpg's and highway speeds? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MjrBummer · 01-29-2015, 01:40 PM

Hey everyone,

I've been looking through a lot of the threads, and I see there are quite a few very talented wrenchers on here.

I was curious about some of the heavy hauler projects though. The C50/C60's for example. I see a lot of them being shortened and getting pickup truck boxes put on them. What kind of highway speeds are you able to achieve with them and what kind of mpg's ar you guys getting? What kind of engine, carb, tranny, rear end gears are you running, etc.

Is there a preferred engine and carb setup people are running? Just looking for opinions on horsepower vs. torque and such. How many are running diesels?

I know, a lot of questions. That happens with ADHD.

I have a 1967 C50 School bus converted into an RV. GVW is 19,500 lbs. I'm running a 327, a 1965 so my Dad says, and a 4-speed w/split rear. The engine is real close to the firewall and I won't be able to get in to see if I can get at the casting numbers until spring when the ground is thawed and dry to find out for sure. I have no clue about the rear gear ration yet.

Any good links to manuals for the brakes, etc.?

Thanks in advance for any input.
Bill

Robert1970C20rstbukt · 01-31-2015, 10:33 PM

As far as shop manuals and literature goes, keep an eye out on ebay. I found an original service manual for my '69 GMC 8500 on there as well as an original owner's manual. My truck has a 7.17 gear ratio because it was ordered as a refinery fire truck, never left the plant so it didn't need to reach highway speeds. It can do about 50 but that's pushing the V6 around 3200 RPM's, way too high. I think the high range of a two speed is higher than that, but there are better gears for highway use available.

colgad · 02-02-2015, 10:05 PM

I had a 72 350 4 speed C50 with a 8.20/6.?? something dual speed rear and I could get to about 55 but it shook to much to go faster but I think it would have reached 60.

My current 67 327 C50 has not been on the road but a small test drives so far and I am going to replace the 327 4 speed with a 5.3 4L60e sometime this year. I replaced the dual speed with a 4.80 single and would expect to get to 70/75 easy. My gas mileage estimate is about 15.

84rzv500r · 02-03-2015, 10:54 AM

I have a max RPM of 2350 on my 8v-71 Detroit running through a RTO-9513 Road ranger (single Overdrive trans) and then through a Rockwell T-1138 Overdrive Transfer case to 7.20:1 axles, I also bolted on 6 new 11R22.5 wheels and tires to help as well,... Before I pulled the 350/5 speed out I could get 60 mph wound out at 4500 RPM with 8.25-20's

the spreadsheet says that the big Detroit @2350 will get me 52 mph in 5th direct (12th gear) and 72 mph in 5th over (13th) and 1800 should be 55Mph and 2100 should be 65... very comfortable RPM for the old girl,,, who is used to pulling 75,000lbs of TD-25 on a 20,000 lb detachable in that old looserville 9000 ford and will retire pulling 12,000 or so of GMC pickup around...

We get 15MPG bob-tailing around in the 69 Brockway 361 twin screw with a turned up 6-71 and a bit better in the 70 Brock 361 Single rear so I expect to see somewhere in the 12-15MPG range at highway speeds.. A bit more motor and in between on the weight and they are 10 speeds with no overdrive (4.33 gears),...
Jimmy in a Jimmy...

MjrBummer · 02-03-2015, 12:57 PM

Thanks for the input guys, I appreciate it.

I haven't been able to take this thing on a long enough drive to see what kind of mileage I'm getting yet.

I could only get to 60mph when I brought her home. it takes several country miles to get her there too. No tach installed yet, but it sounded like she was turning pretty good.

Hopefully rebuilding the tiny carb that's on the engine will help get her up to speed a little quicker and help the mileage. Trying to find a clutch fan to help out the mileage too. I'm waiting for the snow to clear so I can get out into the scrap yards and farmers pastures to see what I can dig up.

Bill

MattBMiller · 02-04-2015, 01:26 PM

Quote:

Originally Posted by Robert1970C20rstbukt

As far as shop manuals and literature goes, keep an eye out on ebay. I found an original service manual for my '69 GMC 8500 on there as well as an original owner's manual. My truck has a 7.17 gear ratio because it was ordered as a refinery fire truck, never left the plant so it didn't need to reach highway speeds. It can do about 50 but that's pushing the V6 around 3200 RPM's, way too high. I think the high range of a two speed is higher than that, but there are better gears for highway use available.

The 2-speed behind my 350 was a 7.17/9.76. The 350 was screaming at 55!!

Swapping out the rear end for a 4.10 with discs.

KQQL IT · 02-05-2015, 02:06 AM

My C-60 366 5+2 cant recall the gear. Spent most of its life @3200

**buggy5872** · 02-22-2015, 10:38 PM

Big Bertha has a 468 cubic inch big block with a 4l80e tranny, 5.38 rear with 9r22.5 tires. She gets 13 mpg empty and 8 mpg with our 11k pound camper. Fastest I ever had it was 97 mpg according to the gps.....I was late to go pick up an Elcamino in NY. I don't think I would try any faster than that. It was a hand full at that speed. Usually I don't run any faster than 70 mph.

MjrBummer · 02-23-2015, 06:50 PM

WOW! I don't want to be running that fast, but it would be nice to keep up with traffic on the highways.

I can't wait for all this snow to go away, and for the warm weather so I can start digging around all the bone yards and farmers pastures for some 22.5" wheels and parts to update the brakes. Then I can get her out on the open roads a bit more to see what I get out of her for mpg's.

I'm going to be checking out the camper/rv salvage yards for a few goodies too. Either that or I'm going to have to custom build some stuff.

Tomorrow I was planning on stopping at my buddies house where its stored to pick up the title to get her registered and figure out how my Dad had it registered so I can see about insurance. Almost time to make some calls for new windshields too.

Bill

kieth · 03-06-2015, 05:09 PM

If you guys want help figuring out what gearing to run call me at my office 918-446-5521 or email me at www.kieth.goudelock@mhctruck.com I can build you some custom spreadsheets that will show speeds with different gearing, tire sizes etc.....I do this for a living but just happen to own older pickups also.....call so I can ask the right questions and get the information correct.

01-29-2015, 01:40 PM	#1
MjrBummer Registered User Join Date: Dec 2014 Location: Chippewa Falls, WI Posts: 41	Heavy hauler mpg's and highway speeds? Hey everyone, I've been looking through a lot of the threads, and I see there are quite a few very talented wrenchers on here. I was curious about some of the heavy hauler projects though. The C50/C60's for example. I see a lot of them being shortened and getting pickup truck boxes put on them. What kind of highway speeds are you able to achieve with them and what kind of mpg's ar you guys getting? What kind of engine, carb, tranny, rear end gears are you running, etc. Is there a preferred engine and carb setup people are running? Just looking for opinions on horsepower vs. torque and such. How many are running diesels? I know, a lot of questions. That happens with ADHD. I have a 1967 C50 School bus converted into an RV. GVW is 19,500 lbs. I'm running a 327, a 1965 so my Dad says, and a 4-speed w/split rear. The engine is real close to the firewall and I won't be able to get in to see if I can get at the casting numbers until spring when the ground is thawed and dry to find out for sure. I have no clue about the rear gear ration yet. Any good links to manuals for the brakes, etc.? Thanks in advance for any input. Bill

01-31-2015, 10:33 PM	#2
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	Re: Heavy hauler mpg's and highway speeds? As far as shop manuals and literature goes, keep an eye out on ebay. I found an original service manual for my '69 GMC 8500 on there as well as an original owner's manual. My truck has a 7.17 gear ratio because it was ordered as a refinery fire truck, never left the plant so it didn't need to reach highway speeds. It can do about 50 but that's pushing the V6 around 3200 RPM's, way too high. I think the high range of a two speed is higher than that, but there are better gears for highway use available. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck

02-02-2015, 10:05 PM	#3
colgad Registered User Join Date: Jun 2006 Location: Lutz, Florida Posts: 838	Re: Heavy hauler mpg's and highway speeds? I had a 72 350 4 speed C50 with a 8.20/6.?? something dual speed rear and I could get to about 55 but it shook to much to go faster but I think it would have reached 60. My current 67 327 C50 has not been on the road but a small test drives so far and I am going to replace the 327 4 speed with a 5.3 4L60e sometime this year. I replaced the dual speed with a 4.80 single and would expect to get to 70/75 easy. My gas mileage estimate is about 15. __________________ 1967 Red, C10 Short Bed 6.0L T5 5 speed 1967 Orange and Black C50 6.2 Detroit Diesel NV4500, 2 Ton Pickup 1972 White, Chevy Blazer 2WD 67 Dog house 5.3 4L65 2016 Power Tour LH 1955 Red-Cream, Chevrolet Nomad, restoration on hold 2004 Black, Corvette Z06 LS6 convertible (Rock solid Fun) 2011/2018 Power Tour

02-03-2015, 10:54 AM	#4
84rzv500r Registered User Join Date: Oct 2012 Location: Elmira NY/Palm Beach FL Posts: 69	Re: Heavy hauler mpg's and highway speeds? I have a max RPM of 2350 on my 8v-71 Detroit running through a RTO-9513 Road ranger (single Overdrive trans) and then through a Rockwell T-1138 Overdrive Transfer case to 7.20:1 axles, I also bolted on 6 new 11R22.5 wheels and tires to help as well,... Before I pulled the 350/5 speed out I could get 60 mph wound out at 4500 RPM with 8.25-20's the spreadsheet says that the big Detroit @2350 will get me 52 mph in 5th direct (12th gear) and 72 mph in 5th over (13th) and 1800 should be 55Mph and 2100 should be 65... very comfortable RPM for the old girl,,, who is used to pulling 75,000lbs of TD-25 on a 20,000 lb detachable in that old looserville 9000 ford and will retire pulling 12,000 or so of GMC pickup around... We get 15MPG bob-tailing around in the 69 Brockway 361 twin screw with a turned up 6-71 and a bit better in the 70 Brock 361 Single rear so I expect to see somewhere in the 12-15MPG range at highway speeds.. A bit more motor and in between on the weight and they are 10 speeds with no overdrive (4.33 gears),... Jimmy in a Jimmy... __________________ --------------------------------------------------------------------------- 72 GMC K5500 Napco 4x4 8V71/RTO-9513/T-1138 71 Corvette Wide Body 502 Ramjet 83 HD XR1000, 99 HD XL1200S, 84 YAM RZV500R 05 MB E55 AMG, 12 45th Camaro SS stick vert

02-03-2015, 12:57 PM	#5
MjrBummer Registered User Join Date: Dec 2014 Location: Chippewa Falls, WI Posts: 41	Re: Heavy hauler mpg's and highway speeds? Thanks for the input guys, I appreciate it. I haven't been able to take this thing on a long enough drive to see what kind of mileage I'm getting yet. I could only get to 60mph when I brought her home. it takes several country miles to get her there too. No tach installed yet, but it sounded like she was turning pretty good. Hopefully rebuilding the tiny carb that's on the engine will help get her up to speed a little quicker and help the mileage. Trying to find a clutch fan to help out the mileage too. I'm waiting for the snow to clear so I can get out into the scrap yards and farmers pastures to see what I can dig up. Bill

02-05-2015, 02:06 AM	#7
KQQL IT At the body shop. Join Date: Aug 2009 Location: Land of fruits and nuts. Posts: 5,253	Re: Heavy hauler mpg's and highway speeds? My C-60 366 5+2 cant recall the gear. Spent most of its life @3200 __________________ " That didnt make it any newer " " Dont antique the equipment "

02-22-2015, 10:38 PM	#8
buggy5872 Senior Member Join Date: Jun 2011 Location: North Beaver TWP PA Posts: 833	Re: Heavy hauler mpg's and highway speeds? Big Bertha has a 468 cubic inch big block with a 4l80e tranny, 5.38 rear with 9r22.5 tires. She gets 13 mpg empty and 8 mpg with our 11k pound camper. Fastest I ever had it was 97 mpg according to the gps.....I was late to go pick up an Elcamino in NY. I don't think I would try any faster than that. It was a hand full at that speed. Usually I don't run any faster than 70 mph. __________________ ___________________________ 1959 Apache Short Fleetside, 1959 Apache NAPCO Long Stepside, 1957 3100 with 59 fleetside bed 1957 5700 LCF Crew Cab "Big Bertha",1959 GMC F370 1958 GMC 600, 1946 Chevy, 1959 Viking 60 LCF 1974 Elcamino SS, 1979 6500 GMC Tilt Bed Wrecker Big Bertha Build

02-23-2015, 06:50 PM	#9
MjrBummer Registered User Join Date: Dec 2014 Location: Chippewa Falls, WI Posts: 41	Re: Heavy hauler mpg's and highway speeds? WOW! I don't want to be running that fast, but it would be nice to keep up with traffic on the highways. I can't wait for all this snow to go away, and for the warm weather so I can start digging around all the bone yards and farmers pastures for some 22.5" wheels and parts to update the brakes. Then I can get her out on the open roads a bit more to see what I get out of her for mpg's. I'm going to be checking out the camper/rv salvage yards for a few goodies too. Either that or I'm going to have to custom build some stuff. Tomorrow I was planning on stopping at my buddies house where its stored to pick up the title to get her registered and figure out how my Dad had it registered so I can see about insurance. Almost time to make some calls for new windshields too. Bill

03-06-2015, 05:09 PM	#10
kieth Registered User Join Date: Sep 2010 Location: Tulsa, Oklahoma Posts: 1,925	Re: Heavy hauler mpg's and highway speeds? If you guys want help figuring out what gearing to run call me at my office 918-446-5521 or email me at www.kieth.goudelock@mhctruck.com I can build you some custom spreadsheets that will show speeds with different gearing, tire sizes etc.....I do this for a living but just happen to own older pickups also.....call so I can ask the right questions and get the information correct.



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