Throwing ideas around - LS swapped Tahoe, built for mpg

[tpass]

Here is my problem with engine swaps; If you need a car now, don't swap an engine into something. If you don't need it now, My choice would be a slight downgrade to a 4.3, those are pretty good on gas (I have a 4.3 Blazer, it get's 18-19 occasionally). But even a downgrade is gonna take longer than a snap of a finger. It's just not justified to me, all this time and effort for 3 MPG.

+1

In these threads about swapping motors for better MPG, I always ask if the cost of the swap is worth the savings? What is the ROI or return on investment? Granted as the cost of fuel rises it makes it more attractive, but its really just an expensive experiment to see if you'll get better gas mileage.

The caveat always being what you have available to you.. maybe you already have the donor veh with harness and ecm/pcm's, all the tools needed to fabricate the adapters and mounts you'll need.. and exhaust

If you have to buy all that stuff, the costs add up quickly.

 

[Erik the Awful]

Last time gas prices were this high (2008), I looked into buying a scooter for commuting to work. I can take back roads and avoid almost any traffic, so the safety issue wasn't bad. Then I looked into buying a used Ruckus, and they were going for about $2500. Gas was about $2 a gallon more expensive than usual, and at that rate it was going to have to save 1250 gallons. At 18 mpg in the Mustang, that's 22,500 miles. On top of that, only about half my commuting days were decent weather for scootering. At the time I was driving about 10-12k miles a year, so I was looking at four years to amortize the gas costs by buying a scooter. Not worth it, so I started driving slower. Six months later gas prices had settled back down and I never considered a scooter again.

 

[L31MaxExpress]

I do not know where you are coming up with 12/16 for mileage figures but they are dead wrong, atleast on a 2wd. My brothers 99 Suburban consistently delivered 20-21 mpg on the highway with the cruise set at 70 mph. My Express van delivered better than 20 mpg on the highway when it had the 350. The 383 has gotten 19 on a long trip and could still use some additional fine tuning. The L30 305 Vortec in my 99 Tahoe pulled down 22+ mpg on several trips despite having heavy P305/50R20s on it. I put a cammed 8.1L and a 4L80E into that Tahoe when the 4L60E gave up and it has gotten 17-18 mpg on trips. I personally would not deal with the headache of swapping in a LS or LT based engine.

 

[yevgenievich]

At least according to built in mpg calculator, averaged 21mpg with a 2018 suburban loaded with people and cargo over 1400 miles. But on my 97 2500 more around 12mpg

 

[Drunkcanuk]

A Tahoe is a lot of vehicle for a V6 or small V8 to be pulling around. If the motor is undersized, you will be using more fuel to get up to speed. Back in the day, woman had a 6 banger Dakota, buddy had the same model with a V8, he got better millage.

 

[94K3500PROJECT]

Torque

I do not know where you are coming up with 12/16 for mileage figures but they are dead wrong, atleast on a 2wd. My brothers 99 Suburban consistently delivered 20-21 mpg on the highway with the cruise set at 70 mph. My Express van delivered better than 20 mpg on the highway when it had the 350. The 383 has gotten 19 on a long trip and could still use some additional fine tuning. The L30 305 Vortec in my 99 Tahoe pulled down 22+ mpg on several trips despite having heavy P305/50R20s on it. I put a cammed 8.1L and a 4L80E into that Tahoe when the 4L60E gave up and it has gotten 17-18 mpg on trips. I personally would not deal with the headache of swapping in a LS or LT based engine.

I’m agreeing with you on this one on about all points.
These trucks if in good repair/maintenance do damn good on highway fuel mileage.
We took my old 96’ K1500 from Michigan to Gulf Shores AL in 18’. At 75MPH with the cruise control on most of the way including hills of Kentucky/Tennessee I averaged 17.6 hand calculated.
That included stops along the way for bathroom breaks etc

Some of these guys just have awful for MPG driving habits or something


An LS swap won’t gain much of anything for MPG

 

[L31MaxExpress]

Torque


I’m agreeing with you on this one on about all points.
These trucks if in good repair/maintenance do damn good on highway fuel mileage.
We took my old 96’ K1500 from Michigan to Gulf Shores AL in 18’. At 75MPH with the cruise control on most of the way including hills of Kentucky/Tennessee I averaged 17.6 hand calculated.
That included stops along the way for bathroom breaks etc

Some of these guys just have awful for MPG driving habits or something


An LS swap won’t gain much of anything for MPG

Agreed, my buddy has a 2006 2wd 1500HD 6.0L with a very mild cam akin to a RV cam and 3.73s. He said he is getting 13.5 mpg out on the road. LS swap is about the least productive R.O.I. for fuel economy. The 350 already makes its torque at a lower rpm and has plenty of grunt to cruise down the highway efficiently.

I found the rolling hills of Kentucky kinda funny. I think everybody with a GM LS based truck in Kentucky has straight pipes. I had the cruise in the van set at 75 mph and my van would just climb those hills loafing along in overdrive and every 5.3 truck was kicking down and rapping the pipes trying to keep from getting passed by a van.

Even coasting along at 65 mph the 350 would climb the grades in overdrive. You would be amazed at how much fuel a LS burns when your foot is mostly into it to climb hills because the LS cannot seem to make low-speed torque.

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[HeavyAsAChevy]

As a previous V6 owner. There wasn’t a V6 LS(though that would have been awesome). It was a great engine, but it couldn’t tow anything. Made decent low end torque, hated a trailer, I also had the 5spd and never got better than 16mpg. I’d get the Tahoe, do an exhaust, high flow air filter, maybe a black bear tune.

 

[Alberniken]

If room and economy are the primary requirements, I would suggest :

2WD rather than 4WD.

Open diff rather than LSD.

CAI and headers.

Low rolling resistance tires.

Lower suspension & front lower air dam; perhaps use flexible belting to get the dam even closer to the road.

A shift kit and a switch to keep the torque converter locked when cruising also can help.

cheers

 

[Cadillac Bob]

I think what one guy said is your best bet get a better transmission newer 8-10 speed. or have one Per se custom made for mpg and also delete anything that grabs air as you would go down the road! To be like a swimmer sleek more aerodynamic get good air filter/intake plus exhaust done. but trans and aero and I bet you’ll not need to engine swap and I would think a newer transmission would be easier to mate with older motor than newer engines to older transmissions?? I’m no car mechanic but really gearing is we’re it’s at if your low rpm’s cruising down highway you should get better mpg and driving easy peasy in the city plus only have half tank when city driving to cut weight down but idk it may just be worth getting a newer gen full size suv and use same tips plus have a light foot might be more cost effective in the end but I’d still like to see what you do end up doing if it’s a modded 400!! Lol look forward to seeing what you do