K30 15-20 mpg?

[Evane201]

Hey guys,

In the past few months I've totally fallen in love with square body trucks. In perticular a k30 SWD. So now I've begun the hunt for the right one for me. This truck is going to be my daily driver so I'd like it to have "decent" mpg. Hopefully in the 15-20mpg range. Now I know that a 454 won't do that for me so I'm either thinking a 6.2l diesel or a cummins swap should do the trick. Which one will yield the best mpg? I don't plan on doing any serious towing and probably not over 100 miles so either motor should be great for me. I also would like to have a 3-4 inch lift with 35" bfg ko2s on a flatbed. Is this a feedable goal or am I just trying for something impossible? And is there anything else I could do to increase possible mpg?
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[geezer#99]

Did you know that starting the same thread in two or more different parts of the forum is a big no-no!

[DieselSJ]

6.2/6.5 with a turbo and an overdrive trans. If budget allows and you have the skills, then cummins. And actually a 454 can deliver that mileage with EFI and an overdrive if you build it right. The new hotness is a LS swap which can give that mileage also. You didn't say how much you want to spend.

[Edahall]

Assuming they are geared correctly, both engines would be capable of achieving that fuel economy. However, the Cummins will probably get slightly better fuel economy, have much more power and be more reliable. Of course, your fuel economy and especially with a lift will be very speed dependent. With my setup, I get high 20's if I drive conservatively. I also use it as a daily driver.

[andrewmp6]

35s and the lift will be the biggest problem really.A diesel swap and gear it right you might see 15 mpg plus

[cadillac_al]

I would plan on 10 mpg and get used to it.

[daddyjeep]

Fuel economy concerns are generally driven by cost. How many miles do you think you will have to drive to recoup the $5,000 plus cost of a cummins swap, or even a $2,000 or $3,000 cost for something else? I was dreaming of a motor swap for mine as well until I realistically looked at the cost vs the gas savings.

[Ziegelsteinfaust]

Like a couple of people mentioned your tires are going to be the biggest blocker of mpg. Even the Ford Raptor which has that size stock only gets decent mpg if you granny it.

So my suggestion is go with the Cummins, and a 5 speed manual. Get a 6 speed if you can swing the cash.

My K20 with all light duty parts really only got 15 hwy if I went 60-65 on 32"AT tires. Any faster, and it dropped like a rock, and slower didn't work well due to mechanical+wind resistance.

I got a hair under 20 one time following a big rig, but how often can you really do that.

So we get down to build progress. Do you buy a gas truck fix it up, and then swap a diesel in. Or do we swap a diesel then build it up.

Personally I say get Craiglist bolt on's for the 454, and fix it the way I want keeping a eye on future diesel swaps. So becarefull​ of gears you buy unless you plan to OD the truck.

A good running 454 should do 12-13 easily with bolt-on's. Also you could use two different sets of rims, and tires. One with a HT tread pattern for mpg, and another for off road times.

[abig84]

Originally Posted by cadillac_al

I would plan on 10 mpg and get used to it.

i wish i could get 10mpg out of my 86k30. last time i checked im getting 7

[Nick_R_23]

Another side of this, is there any specific reason you need oversized tires, a lift, and a flatbed? Anytime you change the aerodynamics of the truck as far as lift, etc, your mileage will suffer. My suggestion if you are trying to improve MPGs, keep stockish sized tires that don't protrude past the fenders (thinner profile tires are best), keep the truck at stock height or even better, a small drop, and keep the stock bed for better airflow across the body. That will gain you better mileage and aero than a large, lifted truck. A 6.2/6.5 is a good suggestion as is an LS swap, 5.3 would be good for you. But as other posters have mentioned, cost is a factor here. A stock 6.2 truck could be found for a reasonable price, but is a 5.3L worth it in terms of cost of swap vs any fuel savings?

[Evane201]

Thanks for your input guys!

The reason behind the lift and the tires is because we get some serious snow sometimes up here in Minnesota. I also ice fish so I need a truck that can get me on and off the ice withought getting stuck. The flatbed was a thought since It would be nice to get 4 dirt bikes up there so I don't have to pull a trailer but if it has a serious mpg affect I can skip that and get by. The one I'm looking at right now has a 350 in it but the valves are off so it doesn't run right. It comes with a new set of heads so I could fix that one up and drive it for a while too. Only problem is that it's a c20. The price is right though so ill have to convert it to a 4x4. My neighbor has done a conversion before so I can get help from him. In the past few months I have only found 1 k30 and I was a day late and a dollar short on that one. There's nothing in decent condition within a 500 mile radius of here haha
https://stcloud.craigslist.org/cto/6045995370.html

[Ziegelsteinfaust]

Here in California they can be had cheap if your up to a road trip.

Also do you have smog laws up there?

If so you can get smoggers cheaper the pre smog.

[Evane201]

I don't think a road trip would be able to work for me since I'm busy with construction during the week and can't get away for more than 2 days. As far as I know there aren't any smog laws in minnesota. There's a k10 with a 6.2 diesel. 35s and a 4 inch lift for sale that might be worth checking out as well. The body is beat to hell but for 3k I could have an 6.2 and matching tranny, tires, a lift, and most of the parts needed for the conversion.

[Nick_R_23]

Sounds like that may be the way to go. Have a truck to start with and fix the body up as you go!

[tucsonjwt]

I you search this forum you will find a dealer advertisement showing the difference in gas mileage for 1/2 ton, 3/4 ton, and 1 ton new Chevy pickups with gas engines. All except the 1/2 ton are estimated to get 10 mpg city/16 mpg highway. I have talked to contractors with new 3/4 ton and 1 ton pickups and they say they only get 8 mpg in town, but they are loaded up to near the max payload.

Where I live in HotZona, diesel is priced at 25% more than gas. So, you would have to get 25% more mpg in a diesel to just break even with a diesel. Plus, diesel engines have more parts to tend to (injector pump, lift pump, etc.) and you need to make sure that you have a fuel additive for the low sulphur diesel now produced.

The best mpg I ever got was 13 mpg highway on my 73 C20 454 with TH400 transmission. (Actually, I got about 17 mpg once when I was driving that 73 out here, along with a 6,000 lb trailer. I had a long stretch of driving downhill in the western mountains and had the wind at my back. )

[tucsonjwt]

One other thing to consider, when you get into the 3/4 ton or 1 ton, a lot of the parts are more expensive than a 1/2 ton. Suspension, brakes, rear axle, etc., are all very pricey, compared to a 1/2 ton.

[meatwagon83]

My c30 gets 15-17 on the open road, I have a 454 built with an eye to mileage, a properly tuned quadrajet and an nv4500, with this setup in a k30 you would probably see 12, your best bet for a 15 mpg k30 is a cummins swap

[Half Assed]

you would be lucky to get 12-13 empty with a 5.9 cummins

[Evane201]

Ok so I did some checking and the truck I had planned to swap onto the c20 is more problems that it's worth. But I believe I have found a better candidate for a parts truck.

https://fargo.craigslist.org/cto/6042912326.html

Now he said it's got 45k and doesn't know if it rolled over but said it's a likely assumption. The interior is actually in very good shape and the parts seem to be all good. There is rust all over so it's not fixable as far as the body goes and I wouldn't be able to salvage the tires which is ok with me. He said that both axle assemblies were replaced after being taken out and any bearings+ U joints that needed to be, were replaced

Now would I be able to switch over the bench seats from the burb to the CC as well as other interior parts? And down the road could I use the 4x4 parts and do a conversion? The engine would for sure be going into that c20 instead of fixing the 350 that's in it

[akart]

Originally Posted by Evane201

Ok so I did some checking and the truck I had planned to swap onto the c20 is more problems that it's worth. But I believe I have found a better candidate for a parts truck.

https://fargo.craigslist.org/cto/6042912326.html

Now he said it's got 45k and doesn't know if it rolled over but said it's a likely assumption. The interior is actually in very good shape and the parts seem to be all good. There is rust all over so it's not fixable as far as the body goes and I wouldn't be able to salvage the tires which is ok with me. He said that both axle assemblies were replaced after being taken out and any bearings+ U joints that needed to be, were replaced

Now would I be able to switch over the bench seats from the burb to the CC as well as other interior parts? And down the road could I use the 4x4 parts and do a conversion? The engine would for sure be going into that c20 instead of fixing the 350 that's in it

Good looking Suburban. I drove a '82 K20 6.2 for about 20 years all I ever did was change the oil, fuel filters and air filter,maybe a bulb or two and put fuel in it.
If it (the Burb)has 145K it is just getting going. Mine went over 300K and would still be going but I wanted to get back to a 350 as they start better in Alaska. I got a mixed mileage of about 16 mpg w/the 6.2. I took the drive line for my 350 project.
The 6.2 was kind of gutless and the 350 is much more fun,14 mpg but I think it is worth it for the snort and ease of working on it and the fun add ons.
I'd drive that Burb. with some skinnier tires 235/85R16 but I would loose that eyebrow thing.
Good luck/have fun.

[Edahall]

Like the previous post, I also drove an 82 Suburban 6.2 diesel for many years. The difference was mine was 1/2 ton and 2 wheel drive. It would get close to 30 mpg driving it easy. This kind of shows you how much penalty there is with the heavier duty suspension, 4 wheel drive and height. I also towed with the Suburban but it was pretty gutless and sucked fuel because you had to work it so hard.

That said, with your application, I think you would be far better off with a Cummins or LSx engine over a 6.2 diesel.

[v30crewcab]

diesel is your only option with a lift and 35 tires. I get 17-19 out of mine with a 400k cummins in it and nv4500.

[Tucson38]

Originally Posted by daddyjeep

Fuel economy concerns are generally driven by cost. How many miles do you think you will have to drive to recoup the $5,000 plus cost of a cummins swap, or even a $2,000 or $3,000 cost for something else? I was dreaming of a motor swap for mine as well until I realistically looked at the cost vs the gas savings.

Well said. "If you want economy you'll have to pay for it".

[wilkin250r]

A wise mechanic once told me "You will NEVER save enough money in fuel to justify the cost of a diesel swap."

[DieselSJ]

Originally Posted by wilkin250r

A wise mechanic once told me "You will NEVER save enough money in fuel to justify the cost of a diesel swap."

My Grand Wagoneer went from 12 to 24 mpg.

Gas - 30 gallons per week x 52 weeks x 2.20/gal = $3432

Diesel - 15 gal per week x 52 weeks x 2.35/gal = $1833

Average savings per year $1599.