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73-87 Chevy _ GMC Trucks => Diesel Engine Discussion => Engine/Drivetrain => Cummins Swaps => Topic started by: wildcatjason on December 26, 2011, 10:22:54 pm
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Just got over a 1000 miles on my 4bt cummins conversion. I just did my first mileage calculation. It's not as good as I hoped for but it is better then the 9mpg I was getting with the weak 350 I will post my numbers in the mileage section too. This is 95% city driving 532 miles/28.32 gallons =18.77 mpg
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That is better than you would get with gas. I am with you, I thought you would get better fuel milage with the diesel. Why do you think it isn't better ?
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Honestly when I said I was hoping for better I was hoping for over 20 in city. This vehicle is a 6000 lb suburban. I am hoping with an alignment and new tires I will obtain my goal. I cannot ask for more really. My wife's little 4 cyl minivan gets 21 in town.
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I would be really curios what a freeway trip would net you.
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I am planning a Cali trip in the next month I'll post numbers then. I should get this thing aligned next time I get paid.
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I am here: http://maps.google.com/maps?ll=37.657747,-97.264011
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Where in Cal. Are you planning on visiting ?
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I don't know yet I'm going to do a nursing travel assignment there soon. Most likely south.
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No one has posted here in awhile and I have posted this in another area, for those of you interested this was the last fuel mileage I obtained with new tires and alignment with strictly in town driving.
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No one has posted here in awhile and I have posted this in another area, for those of you interested this was the last fuel mileage I obtained with new tires and alignment with strictly in town driving.
Picture isn't working but it says 20.14 mpg.
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got a question, do any of y'all know where i can find casting info for the 6.2L.
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Here is a little math work to put that into one money saving scenario:
That 9 mpg avg. to 19.5 mpg avg. in my neck of the woods is just under 18 cent/mile decrease in fuel cost ($3.42 unleaded to $3.96 diesel). I drove my truck a little under 10,000 miles last year so that would be almost $1,800 savings per year. This assumes you don't drive it more now because you get better fuel mileage.
My 11 mpg avg. to your 19.5 mpg avg. at the same 10,000 miles per year is about 11 cents per mile so about $1,100 per year savings.
How much do you think you have in the conversion? Are you running an overdrive transmission? 4X4 or 4X2?
Sorry for all of the questions, I am just not familiar with your truck or any conversion posts you may have. Suppose I probably should have done a search before I started this response.
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Wow that is crazy good.
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I have an 87 half ton suburban with a 6.5 banks turbo, 700, and 3.73 gears rolling on 285/16's. Drove it from southeast Idaho to San Fransisco last march, spent a week chasing around the area, (daughters college softball games), and sight seeing. Had the wife and two teenaged boys plus luggage. Was a 2200 mile trip, we averaged 18.5 to 19.5 driving there and back and the week spent in town it did 14.5. I was pretty happy with it. We had an 07 burb/5.3 and on a trip to Vegas it only got 16.5 driving down and back, didnt check it in town. 20 in town sounds pretty good to me, I have a friend that just did a 75 ford 3/4 ton 4x4 to a 5.9 cummins swap, he has an NV4500 and 3.50's gears and he is getting around 20 with it doing mixed town and freeway driving. He also has a 4BT in the same vintage half ton 4x4 with no overdrive and he gets about 19 with doing the same type of driving. I did a Geo Tracker conversion about 4 years ago, used a VW 1.6 turbo motor in it. Its my chase around the farm vehicle and it consistently gets 25, the best I got with it was 32, its a fun little outfit.
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got a question, do any of y'all know where i can find casting info for the 6.2L.
Give me some time----i can't guarantee anything either----as usual another crisis has cropped up.
i think the latest 6.5's are actually made or redesigned by international----the big truck makers and these blocks are supposedly the best out of the crop.
But give me a few hours or days or months.....
P.S. we should start a new thread because this is a little off-topic.
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Your fuel economy is not bad at all for all the city driving. These are not exactly light weight vehicles so they take a lot of power to get up to speed. I bet you can get over 30 mpg on the freeway with your combo and driving easy. Best fuel economy is around 55-60 with these square nose trucks. I drive almost all freeway so I can't comment on what kind of fuel economy my 6BT Cummins Suburban would get under the same circumstances as you. However, I'm getting about 25 mpg on the freeway driving easy. I also just swapped out the wide tires for some 265/70/17's so hopefully, I'll pick up a mile or two.
I think I remember you saying you advanced the timing. That's helps some.
Since you do a lot of city driving, you might think about installing a lower stall converter. Did you install a diesel converter? Those are OK, but there are even lower stall converters out there. The lower the stall, the less waste from slippage. The Cummins has so much torque that slippage from a converter is not necessary for it to build power.
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Here is a little math work to put that into one money saving scenario:
That 9 mpg avg. to 19.5 mpg avg. in my neck of the woods is just under 18 cent/mile decrease in fuel cost ($3.42 unleaded to $3.96 diesel). I drove my truck a little under 10,000 miles last year so that would be almost $1,800 savings per year. This assumes you don't drive it more now because you get better fuel mileage.
My 11 mpg avg. to your 19.5 mpg avg. at the same 10,000 miles per year is about 11 cents per mile so about $1,100 per year savings.
How much do you think you have in the conversion? Are you running an overdrive transmission? 4X4 or 4X2?
Sorry for all of the questions, I am just not familiar with your truck or any conversion posts you may have. Suppose I probably should have done a search before I started this response.
I don't get on here to often so sorry for the delayed response. The reason I decided to do the swap was because my whole drivetrain was wearing out, so i was going to put money into a diesel swap or to go through the existing tbi 350. I have a ford zf5 behind it with a valair clutch. Its a very nice shifting close ratio tranny. That 19.5 is only city driving. I am mid 20s on the highway. It is a 2wd 3.42 geared burb. I have 6000 into it with a completely rebuilt drivetrain and a fiberglass tilt nose on the way. Hoping get near 30. If you're interested go to www.4btswaps.com. There is more then you'll ever want to know about that engine.
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Your fuel economy is not bad at all for all the city driving. These are not exactly light weight vehicles so they take a lot of power to get up to speed. I bet you can get over 30 mpg on the freeway with your combo and driving easy. Best fuel economy is around 55-60 with these square nose trucks. I drive almost all freeway so I can't comment on what kind of fuel economy my 6BT Cummins Suburban would get under the same circumstances as you. However, I'm getting about 25 mpg on the freeway driving easy. I also just swapped out the wide tires for some 265/70/17's so hopefully, I'll pick up a mile or two.
I think I remember you saying you advanced the timing. That's helps some.
Since you do a lot of city driving, you might think about installing a lower stall converter. Did you install a diesel converter? Those are OK, but there are even lower stall converters out there. The lower the stall, the less waste from slippage. The Cummins has so much torque that slippage from a converter is not necessary for it to build power.
It's a 5 speed. I also found a fuel leak when my kdp fell out. In the process of replacing the timing case and installing a fiberglass front nose.
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Also, add a little bit of transmission oil or 2 cycle motor oil to your diesel. I use 1 oz of the oil for every 2 gallons of diesel. I heard that it helps to restore some of the fuel economy loss from the Ultra Low Sulfer reformulated diesel.
These trucks are also very sensitive to highway speeds. With the high price of fuel, I keep my speed to no more than 60 mph for best fuel economy. Back when diesel was cheap, I used to drive 75-80 mph with my 6.2L Suburban and it would only get 20-22 mpg. However, since then, I have broken 30 mpg driving a steady 55 mph.
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Also, add a little bit of transmission oil or 2 cycle motor oil to your diesel. I use 1 oz of the oil for every 2 gallons of diesel. I heard that it helps to restore some of the fuel economy loss from the Ultra Low Sulfer reformulated diesel.
These trucks are also very sensitive to highway speeds. With the high price of fuel, I keep my speed to no more than 60 mph for best fuel economy. Back when diesel was cheap, I used to drive 75-80 mph with my 6.2L Suburban and it would only get 20-22 mpg. However, since then, I have broken 30 mpg driving a steady 55 mph.
Im a still a lead foot. I also had schieders diesel treat. The quantity is more expensive, but since you can add 4 oz to a full 30 gallon tank it turns out being very inexpensive in comparison.
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A couple of weekends ago I got a quite a few miles on my 6bt Cummins Conversion, seems to average around 21 mpg (mix of city and highway) which I was pretty happy with considering what it is. Its a mildly built (370 hp / 875 ft-lb), 6" lift, 35" tires, dana 60, NV4500.
Now only if diesel prices would come down a little bit...........that 21mpg would look soo much better vs a gas motor.
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A picture of the truck....
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That is a sharp looking diesel, 21 MPG is not too bad at all. One of these days I might just have to get me a diesel.