5.3 or 6.0 ls dilema

[theuglyduckling]

i've got a 76 shortbed stepside RWD i use as a daily driver. Its a bit rusty and has a decent running 350 with a TH350 backing it. Factory gearing out back as well. I've been throwing around the idea of doing an ls swap. I would really prefer the comfort, convenience, and reliability as well as efficiency of doing an ls swap. Plus the cool factor is a nice touch. I am really just looking to make a nice streetable fun reliable truck that has some power for when i want to play a little and is there when i need it, but is dialed back enough for the perfect daily driver to cruise to and from work. I dont have time to do it myself or the resources at hand so i am going to be out sourcing this swap. I was quoted an out the door price of 4500 for the 5.3 and 5000$ for the 6.0. I will be doing some periodic towing of a boat and such with it as well(yes it will be lowered but not slammed to the ground). I will back either with a 4l60e most likely( i would go 6 speed manual but that makes for an uncomfortable ride for the lady when out on date night). Im looking to get recomendations from those who are either also planning or have done both swaps. (i like the idea of removing all decals and having just a 6.0 decal on the side). Ideas, opinions, facts..... send em my way

[Bigstevex4]

Had a 99 Z71 reg cab long box with 5.3 put a k&n and cat back thing ran strong got great milage 17 on the hwy. Only thing that i didnt like was seemed a little week low end. Had an automatic say you would turn a corner had to mash gas to go then it would shift down screem. 2002 took a differnt job same company. got a 2002 Hd ext cab long box 6.0 man ran the hell out of it i load so many cutting edges in it it would be on bump stops still run 70 up Hog back I 70 denver. Put 188 thosand on it till they sent it off. Got a new ford Worst day of my life! Any way it all comes down to more power vs fuel milage in my book.

[theuglyduckling]

the guy doing the swap says i'll get around 21 highway with the 5.3 swap and around 18-19 with the 6.0. Both are far better than my 350 right now, but not enough difference between the two to really make the fuel mileage a deciding factor.(these engines are well tuned and rebuilt prior to swap)

[Bigstevex4]

In my opinion that would be best possable case milage. I have a heavy foot Never really checked the 6.0 wasnt buying the gas but i quarunty it was nothing close to 19. My dad had a 4 door short box 2500 with 6.0 the average milage was 15 untill i drove us down Vegas and back then it was 14.9. God bless his soul swore i ruined his milage.

[77c10]

If & when I get around to doing an LS swap in mine there will be a 6.0 between the frame rails. Of course mine is not a daily driver either.

[bnoon]

The 2500 drivetrain is way worse than a '76 rear wheel drive. Even the full time awd SS I had tuned to 21-22 MPG with E85 and a 6.0 in my 2003 Silverado SS. With 2wd and either the 5.3 or 6.0 expect easy mid 20's highway.

For me, the 500 bucks difference I'd get the 6.0. It's just 30 something horsepower and tq that you'll use all through the whole RPM range in stock configurations. Since I am modifying mine, I went with the 5.3 since it will meet my hp/tq goals and the difference in initial cost would be a waste.

[theuglyduckling]

i will eventually modify out either engine at some point. Initially before install there will be a cam swap and maybe one or two other things. He does nothing but these swaps so his EPA numbers are pretty good. My truck averages 12-13mpg so both engines would be an upgrade. I have a heavy foot as well though, hence why mileage isnt the main factor. I will also be swapping in a posi rear that better fits the application. My current drivetrain is just not ideal for highway(freeway) driving with passing power, and comfortable cruising speed, rpm, and economy.

no matter what im doing the swap, just a matter of whether or not the 6.0 is worth the added 500 bucks, since i will eventually continue to build the engines up more

[Tilt]

For the extra $500, it would be a no brainer. 6.0 all the way. That being said, lots of folks go with the 5.3 and are plenty happy with it. Although I've never heard someone say that they wish they would have went with a smaller engine.

[MalibuSSwagon]

I just bought a junky 2000 Silverado with a 5.3, 148k miles but runs perfect no check engine light. Should be enough power, my Dad has a 2k Z71 with a 5.3 we've used many times to haul cars and it has enough juice to get the job done. I'll be hooking it up to my SM465 so that'll just uncork it that much more compared to the automatic. If I need more power, then supercharger.

[Bigstevex4]

So i got a little over 17MPG with a 5.3 in a more aro dynamic truck with a topper on cruz control over a 400 mile strech interstate . And the same eng in a square body going to get 8 mpg better. Guess you guys gas is way better than ours.

[theuglyduckling]

well this is what he has gotten feedback on some of his getting. anything modern is going to be more efficient than the setup in my truck right now. im not simply looking at fuel economy either. Part of the issue is not how much fuel my setup now burns, but more so the higher RPM's it runs just to mostly keep up during all my highway driving. I want more than 3 gears, and i want modern powertrain. If fuel economy was my goal there wouldnt be any need to discuss this, it would be 5.3 all the way. im more so looking at which engine would best fit my application taking into account the 500$ difference between the two.

[Bigstevex4]

Originally Posted by theuglyduckling

well this is what he has gotten feedback on some of his getting. anything modern is going to be more efficient than the setup in my truck right now. im not simply looking at fuel economy either. Part of the issue is not how much fuel my setup now burns, but more so the higher RPM's it runs just to mostly keep up during all my highway driving. I want more than 3 gears, and i want modern powertrain. If fuel economy was my goal there wouldnt be any need to discuss this, it would be 5.3 all the way. im more so looking at which engine would best fit my application taking into account the 500$ difference between the two.

No man no problem some one else was claiming mid 20s your just going by what you were told. They don't even claim that with new trucks with a v6.
I better just leave it alone.

[theuglyduckling]

I could see maybe gettin right around 20 if I tune it out right and am light on the pedal. But in all reality with a fresh swap I know my foot will be getting into it often to play around with the new power. Really it comes down to of a 6.0 over the 5.3 is worth the 500$ for a mostly daily driver and cruiser I can romp on when I'm out to play.

[bnoon]

Originally Posted by Bigstevex4

So i got a little over 17MPG with a 5.3 in a more aro dynamic truck with a topper on cruz control over a 400 mile strech interstate . And the same eng in a square body going to get 8 mpg better. Guess you guys gas is way better than ours.

93 octane I pulled 24 in my Silverado SS, and on full E85 I pulled 21 to 22. Stock tune could barely do upper teens on 91 or 93, and wouldn't handle e85 of course.

[greg64]

It seems pretty well established that the 5.3 gets better mileage than the 6.0. A buddy of mine at work had a half ton with the 5.3 and pulls his 28' RV with it. He said it'll pull it, but it's really working on the mountains. So he sold it and bought basically the same year truck, that was a light-duty 3/4 ton with a 6.0. Said the 6.0 now pulls the trailer easily.

[MalibuSSwagon]

My Dad's 2000 Z71 with the 5.3L gets between 18-22 MPG depending on conditions. And like I said, I've towed a few cars with it, pulls easily. I also hear from guys with 6.0L trucks and vans that they get between 10-14 MPG.

Now, with that in mind, I could see getting 20 MPG in a square with the 6.0L, considering the square is a 2WD 1/2 ton.

[dukkie]

At only +$500 more get the 6.0 and be done.
Ignore all the gas mileage comments, know that the 21 and 18-19 are unrealistic numbers cause anyone swapping a motor for more power is going to use that power increase and remove all chances of high MPG.. Know this and get back to the original question…
the question is about power. with the 6.0 you will have no concerns about power ever, the 5.3 you may find you wish you spent the extra $500. From around here the price differences are more like +$1000 to get the 5.7 or +$1500 more to get the 6.0. Remember there is no replacement for displacement.

[theuglyduckling]

Very true on the power/economy view Dukkie. The6.0 should give me more out the door initially in the swap either way and adding to it would just make one gnarly little truck. For 500 it seems rather worth it. I feel like I'll be happier with the 6.0 output at it's base instead of the 5.3 that would probably have me wanting more in a shorter amount of time. Realistically my truck is crazy light(compared to current trucks the 6.0 comes in) so comparing economy ratings on my old to the new trucks seems a bit stupid. (Less weight better mileage duh.) I do appreciate the input. Seems for 500 the 6.0 is far worth it. No problems finding them here. I'm paying to have it all done(find, build, instal engine and tranny)

[Tilt]

Another thing to think about is the 4L60. Alot of people say that the 4L60 will not live long behind a 6.0, even it is built up. There are a few here that run the 4L60 behind the 6.0 and have never had a problem. I guess it's kinda of a gamble if you plan on beating on it often. Personaly, I'm going with the 4L80. The 80's do rob more power though.