Throwing ideas around - LS swapped Tahoe, built for mpg

[tksoldierx]

Looking to buy a GMT400 4dr Tahoe to be my family runner.

GMT400 for ease of service, good looks, widespread parts for easy customizability, and familiarity all in one. Plus they’re a lot cheaper to get than most vehicles of similar size.

4dr Tahoe to fit all the family and all the stuff we end up having to bring with us when we travel, without having to try to teach my wife how to back into parking spots with a land yacht of a suburban

We have a 95 extended cab, but it’s a PITA to try to travel with the family in the backseat (No 3rd door offered for 95s). And it has a 383, so it’s a gas guzzler.

The wife’s hybrid is too small to even fit us & the stuff we have to take with. Gets great mpg but very little cargo room and develops a bank-breaking issue every couple thousand miles.

So a GMT400 Tahoe would be the ideal vehicle in shape, size, and design for us. However, stock 95-99 Tahoes get 12/16mpg. Not great with current gas prices for a new family that ends up taking 1600mile round trips every other weekend or so (extended family). Especially when my wife only babysits once in a while and I’m going to be transitioning to running a contracting business on my own soon.

Weight reduction and little upgrades can only take a half-efficient engine on a heavier platform so far with fuel efficiency. So, my current thoughts are to buy one anyway and swap a fresh crate motor in for increased reliability and (hopefully) optimal fuel mileage.

I may be wrong, but my line of thinking is that an LS V6 would get the best mpg when not hauling any real weight. I don’t care about GVWR going down, I already have a work truck. The most work the Tahoe would be used for would be taking a load of materials home from Menards or going down a prairie trail somewhere.

Does anybody have any advice on which V6 would be the best fit in a mileage-based build? Or anything else I should take into consideration for fuel efficiency and vehicle selection in general?

 

[0xDEADBEEF]

I don't think there is an LS based V6, there is an LT based V6.

If I was going through the trouble to swap a Gen V, I would get the 5.3 L83. It gets 22 mpg in my wife's Yukon but that's with the AFM enabled. It probably costs the same as the V6 if you are getting a crate engine.

 

[454cid]

I would look for a used engine, with PCM and wiring harness. A crate engine is going to be expensive, and will simply be a long block, to which you'd still need to add many many parts.

I wonder if a 4.8L gets any better milage than the 5.3?

 

[AuroraGirl]

RWD and 4l60 mate a 3800 not only will you have room for it, if you use a supercharged one and practice good discipline, you can get crazy good MPG. however, I wouldnt know what kind of ratio or tire size youd need to make best use of the engine without putting it into a lugging scenario.

the reason for my recommendation is: camaro or firebird pcm and setups exist period that control 4l60e and 3800(albeit not supercharged), its incredibly simple engine (small block buick derived), good low end and high mileage certainty, and LOTS of upgrade and aftermarket. LOTS of tuner support. LOTS of custom application mounts, adapters you name it. otherwise I say atlas i6 swap. I know very little to the how, but its more modern and its not a bad powertrain. although i hear they arent exactly suited to best utilize their i6 design, they dont fail either. (apparently late i6 atlas used LS pcms)

Alternatively, I5 from a Colorado

Hell, you asked for V6 I gave you a V6, I6, and an I5
If I keep going we are gonna end up at a 2 cylinder 2 stroke so I will stop now

 

[94K3500PROJECT]

MPG is going to be gained in the gearing and transmission as well.

Guys are getting real world 16-17mpg out of the pushrod 7.3 gas engine in new super duty’s and that’s largely because of the 10sp transmission

 

[letitsnow]

I've not (consistently) gotten more than 17 mpg with any full size truck no matter how nice I drive. Have had 6.0's, 5.3's, 5.0's, 4.8's, old 4.3's, new 4.3's, 5.7's. Usually 15-16. They are just too big.

My last attempt was a 2006 silverado 2wd with the 4.8. On paper, that truck should have been fairly efficient. It wasn't. 17 mpg. Was 16 mpg before a BB tune. Wasn't fast, wasn't efficient - just another learning experience.

Maybe you will have better luck.

 

[stutaeng]

Agree. There was never a "LS V6", least not a Gen III or IV. The latest generation 4.3 is LT-series. Some call it Gen V LS.

The last iteration of the 4.3 "SBC"-base through 2013 did get a distributorless & coil-on-plug ignition. I think that was on the GMT900 trucks. HP/TQ I don't think changed much though. Still had iron heads IIRC:-(

I did a 4.3 Vortec to 5.3 Vortec swap on a 99 NBS ECSB Silverado. I've been driving for the last month on a daily basis and it doesn't honestly seem like it gets worse mpg than the V6 did. At least not enough to motivate myself to try to calculate it. Highway it may be a bit worse.

Last week I corrected the tune to the actual 3.42 the truck has because my speedo was reading too low; was initially calibrated to 4.10)...well I'd be darn, turns out I've been driving too darn fast on the 'ol Chebby!

Have you considered a minivan? Our 2013 Town and Country got like 25 mpg on long highway trips, maybe 26? I can't really remember. Great room for the kids and low step-in height.

Full size trucks of this generation are not known for gas sippers.

 

[AuroraGirl]

Agree. There was never a "LS V6", least not a Gen III or IV. The latest generation 4.3 is LT-series. Some call it Gen V LS.

The last iteration of the 4.3 "SBC"-base did get a distributorless & coil-on-plug ignition. I think that was on the GMT900 trucks. HP/TQ I don't think changed much though. Still had iron heads IIRC:-(

I did a 4.3 Vortec to 5.3 Vortec swap on a 99 NBS ECSB Silverado. I've been driving for the last month on a daily basis and it doesn't honestly seem like it gets worse mpg than the V6 did. At least not enough to motivate myself to try to calculate it. Highway it may be a bit worse.

Last week I corrected the tune to the actual 3.42 the truck has because my speedo was reading too low; was initially calibrated to 4.10)...well I'd be darn, turns out I've been driving too darn fast on the 'ol Chebby!

Have you considered a minivan? Our 2013 Town and Country got like 25 mpg on long highway trips, maybe 26? I can't really remember. Great room for the kids and low step-in height.

Full size trucks of this generation are not known for gas sippers.

But then hes stuck with an FCA minivan

 

[Erik the Awful]

It's gonna take several 1600 mile trips to amortize the cost of an engine swap, plus you'll be fighting reliability until you get it nailed down, and then factor in that gas prices are already falling.

I'd make minor mods to the truck as it sits to optimize fuel economy. Lower it, make sure the under-bumper air dam is intact, run narrower tires, and get a tune. Got a roof rack? Delete it. Learn all the hypermiling tricks, like keeping your foot light on the gas.

 

[RedneckWithPaychecks]

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.