[jdemaris]

What if you had 2 80's K20s one gasser 5.7L one diesel 6.2L, and put 1500lbs in each one, same trannies, gear ratio and tire size .... normal driving say 1/2 highway 1/2 around town stop and go.....
Which truck would get better mileage?

And if the 6.2 got better mileage would it be enough to offset the difference in cost?

I've got a 78 K5 Blazer with a 305 gasser, 3.08 axles and a four speed HD man. trans. No OD. With a load of firewood stacked to the ceiling it gets around 11 - 12 MPG. Same with my 83 K5 diesel with 3.08 axles and a TH400 gets around 16 MPG doing the same. Heck, my 65 Chevy Bel Air with a 283 gasser and PowerGlide trans only gets 13 MPG on the highway.

 

[Yellowk20]

These are pretty good numbers considering all the rotating mass the 6.2 has to get rolling.

Heck if it's possible to get these numbers with a 84 k20 then all the more reason to take the spare motor I have and put it in the k20

Its About 80% Highway driving . I've checked every tank of fuel thats been through that truck in the last 65,000 miles and have never gotten less then 16 Mpg.

I use the truck to commute from Wasilla AK to Anchorage AK . I buy my Diesel from the Same store and same pump I fill it right up to he Vent line every time I get fuel , I dont rely on the "first shut off"

My winter mileage is around 19 mpg, but I attribute that to having my front hubs locked in and the lower energy content of #1 fuel

 

[koots]

A J-code 6.2L in good state of tune, should tow as good or better than any SBC from its era. I am confident that it will get better mileage in every instance as well.

 

[jdemaris]

A J-code 6.2L in good state of tune, should tow as good or better than any SBC from its era. I am confident that it will get better mileage in every instance as well.

Better fuel mileage with a 6.2 for sure. But a 350 gasser will easily outpull a J-code 6.2. So will a 400.

A C-code 6.2 has the same horsepower and torque as a 305 gasser. A J-code slightly more.

My 78 G van with a 350 gasser and 2 barrel carb pulled much better then my 87 J- code diesel Suburban. Big difference on hills. But pulling a 5000 lb. trailer the van got 8 MPG and the diesel Suburban got 12 MPG. My Dodge-Cummins does the same and gets 14-15 MPG.


GM 379 (6.2) diesel - 130 HP @ 3600 RPM and 240 lbs. TQ @ 2000 RPM, 3.98" bore and 3.8" stroke


GM 6.2 J-code - 148 HP @ 3600 RPM and 248 TQ @ 2000 RPM
GM 305 gas - 150 HP @ 3800 RPM and 248 lbs. TQ @ 2400 RPM, 3.7" bore and 3.48" stroke

GM 350 gas - 165 HP @ 3800 RPM and 275 lbs. TQ @ 1600 RPM, 4" bore and 3.5" stroke

 

[Gasoline Fumes]

banned from Canada.

How did that happen?

 

[jdemaris]

How did that happen?

Caused by massive anti-terrorism info-sharing between borders. I've worked in Canada and my wife went to college in Canada. I've been crossing through . . from New York to Michigan for many years. I also have the "enhanced drivers license" that takes the place of a pass-port. On our last trip at the border - with no warning -they took me away from my wife and little kid - and put me in a small room while they got ready to transport me to jail. Why? They found records of me being arrested in New Jersey in 1969 as a teenager. So yeah, I was sort of a juvenille delinquent over 40 years ago with no trouble since. Drinking beer, bar fighting, etc. The records did not tell them if I was ever convicted of anything. So, they grilled me with a thousand questions and were furious that I would not tell them what my sentence was. The truth is -all I got at that time was some sort of probation and I don't even remember what the exact charges were. When I told them I did not remember, they got furious. Especially on young hot-headed newly minted immigration cop. After 6 hours . . they "deported" me. That means they walked me 100 feet across the border to the USA immigration station. After that the US officials told me that is happening a lot lately.

When I was "deported" I was told that if I ever try to cross any Canadian border - I will be put in jail, then in a few weeks brought in front of an immigration judge, etc, etc. Are these guys nuts? My entire familly has proper ID. We were trying to cross a normal crossing place. We answered all questions. Yet now I'm a criminal to the Canucks?

One last thing they told me. If I pay them $500, they will give me a 5-year waiver. Screw them. Now when leaving NY to go to Michigan, I drive an extra 100 miles and go through Ohio instead. Good by Canada.

 

[koots]

Well you are welcome in MY Canada :beerchug:

In my experience with my K5 it is all around town, no highway stuff. So my little K5 has diesel torque to motivate a load to move. I had much better experience towing with my K5 than the TBI 350 Burb we had at work. My truck is older and has more miles too.

This is my experience towing heavy loads with my K5. I don't haul long distances or anything. Heaviest I've hauled was a fully loaded bobcat and bobcat trailer, around town while I went around snow blowing driveways (snowblower attachment is badass) and it could haul it, but the chassis and suspension were definitely arguing with it LOL

 

[smackzed]

It's a 2 way street. A guy I worked with rented a condo in Orlando or whatever, packed up his family and was on his way to Disneyland for March break. Got to the border and was denied entry for an assult charge (bar fight) when he was 18 or 19. No problems with vacations in Mexico or the dominican but the US doesn't want him. Oh well.


To the original question. My truck has th400 and 4.1 gears. I get a consisten 18mpg (american gallons) using #2 diesel. In the winter it's down to 16mpg (this is all averaged over the course of each year. Self employed so I keep my fuel receipts and keep track of the miles on the truck). I always have at least a few hundred pounds in the bed. Not a lot but definitly not empty. I also frequently have 1500lbs or more in the bed. In the past I've had 2 305s, both TBI. I got 12mpg with NP833 and unknown gearing (although I was young and heavy with my foot) and 13 maybe 14mpg with th375 and unknown gearing (both were 1/2 tons with 5 lug wheels so I'm sure they weren't geared as low as my current truck) I once got 10L/100km (24mpg) with my current truck driving on almost flat land doing 80km/hr (50mph) There was no wind and only 2 stop signs on the trip. I couldn't drive like that all the time however.
If MPG is your main focus then you can get close to 25mpg with a 6.2 but probaly not much over 20mpg averaged out.

 

[dieseldoft]

well comparing numbers to the more modern 4bt or 6bt cummins engines its not that bad mpg on the 6.2D considering its a generation older then the cummins.

so well the truth comes down to that ill be lucky if i get it to run over 20-22mpg
but well thats still what i hoped to hear.. now its just the hard way to find a good object..
Chevys are not that common here and i rather wait to find a good object instead of getting fooled like my old diesel project that turned down to be a "lets paint over the rust" kind of car.

 

[jdemaris]

well comparing numbers to the more modern 4bt or 6bt cummins engines its not that bad mpg on the 6.2D considering its a generation older then the cummins.

The "B" series Cummins came out a year so earlier then the 6.2 diesel came out - around 1980. It's not about generations. More about what these engines were built for. 6.2 is a lght-duty, short-stroke engine never intended for HD use. Cummins is long stroke heavy-block engine and was always intended for truck and tractor use.

6.2 uses the Ricardo Comet precombustion chamber system for an indirect-injection system. Cummins uses direct-injection as do many other diesel engines from the 1960s and older. John Deere went to DI around 1965. Ford had DI diesel engines in the 50s. Perkins DIs since early 60s, at least.

 

[jdemaris]

What if you had 2 80's K20s one gasser 5.7L one diesel 6.2L, and put 1500lbs in each one, same trannies, gear ratio and tire size .... normal driving say 1/2 highway 1/2 around town stop and go.....
Which truck would get better mileage?

Here is one interesting comparison. A K5 Blazer with a camper body on it. I have two that have been swapped with diesels. Chevy and GMC dealers sold them for two years late 70s. Chevy Blazer Chalet and GMC Jimmy Casa Grande.

I have a road-test done by a 4WD magazine in Feb, 1977. So, the Blazer-Chalet (camper) with a 400 c.i. small block gasser, TH-350 trans and 3.08 axles got 10.4 MPG for their overall test trip. Said to be mostly highway but with some mixed driving. So maybe 11 MPG on a pure highway run?

I also wonder how accurate their figures were. I had a 1/2 ton 1977 G van with a 350 and TH350. It never got better then 11 MPG on any trip when empty.

Same Blazer/Jimmy rig in 1977 was also available with a 350 and a four-speed HD manual trans. I wish I had some test results for that setup - but have never found any.

My 1986 Blazer with the camper, 6.2 diesel and Banks turbo, 3.73 axles and a 700R4 trans gets a best of 16 MPG and around 14 MPG with "mixed" driving. Note I used to have 3.98 axles in it and the MPGs were just the same. Much better driver now with the 3.73s.

 

[BigMike8504]

My truck is 4x4 C Code engine 3.73 gears with a TH700 OD with lockup converter on 31 inch tires. She gets a honest 18 all around average in complete stock form. I did get 24.4 on a 70 mile highway pull at 60 MPH in the heat of summer. I do not get in a hurry and just sortta chug along. Hope this helps, Mike