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Discussion Starter · #1 ·
Any MPG numbers for both these trucks. I'm looking to get in the next few months and I'm leaning towards the big block. From the numbers I get from 1/2 ton Sub's, I'm betting the 454 doesn't get much worse mileage in the big body Suburban.


3/4 ton is something I want if spending the money to get bigger u-joints, axles both front and rear, wheel bearings, steering components, and the 4L80E trans.
 

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Discussion Starter · #2 ·
I didn't want to make my first post to long that way guys will read it :)
Anyhow 'IF' the smallblock 2500 Burb' getts 3-5mpg better I would consider it for SURE.....I really enjoyed the 5.7 vortec in the Z71 I had. And honestly I liked that truck much better than the crew cab D'Max I had for a bit.

However part of me welcomes the challenge and project of making the 454 get the best mileage possible.
I'm thinking that strait away a custom tune would be in order. Then verify the cats are in good condition and then dump them into a single 3.5" pipe with a 3.5" Muffler. (undecided-would like something different than the Flowmaster sound, and NO drone at highway RPM's) Then a 3.5" tailpipe.

Then 265's to replace the 245's (lower rpm) mounted on the forged PYO's to reduce weight. And I really like the look.

After that I would be entering a realm of big $$ for little MPG returns.

Of course proper maintenance would be in order....Beyond the typical plugs/cap/rotor/wires. New injectors, FPR, o2 sensors, clean the MAF things like that.
 

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The Treasure State
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Can't give you much input on the mileage difference between a 454 and 350. But I would bet by the time you figure in the 4l80e behind the 350, not only will it probably get a few less miles to the gallon than w/ the 4l60e, the 350 will really feel like a dog.

I would then factor in the fact that the 5.7l Vortec fueling system is junk. Those stupid poppet injectors were an abomination new. The 7.4l uses real normal injectors with a nice big intake with long runners. From what I have read, what is keeping the 7.4l Vortec from really being woken up is a good tune and some free flowing heads and headers. Those three things will take it from being a big block pig to a damn scary torque monster. I would venture to guess that it would bring up the mileage some too.

If it were my rig, and you were already going for the 2500 version, get the 454.
 

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NCOR
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I've had the L31 (5.7L Vortec) in my rig both near stock and modified including putting an 80e behind it. I could get 14mpg on the highway turning some big tires through the 80e provided I kept to 65mph which was probably about the best it ever got.

One of my friends has a CCLB 98 with the L29 (7.4L Vortec) and he drives hard and pulls ~11mpg consistently in that big truck but gets about 8 pulling his trail rig.

Not a direct comparison but maybe it will help.
 

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HOT AIR BALLOON OWNER
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454, no way I'd want a 3/4 ton w/ a small block.

Maybe it has a 3.73:1 for better freeway RPM. Just don't drive 80mph and expect 20mpg
 

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HOT AIR BALLOON OWNER
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Hell, what about a late 6.5 Turbo diesel? Better TQ, Better Economy.
 

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Discussion Starter · #11 ·
Believe me my first thought, was a 6.5 TD.....I miss the 'Max I had, and can't afford one again. But the 6.5 is no Duramax in power, and it doesn't have the best reliability record. I'd like to have a truck that I can take anywhere and not worry about getting stranded in a bad way..

The other reason I want to stray away from them is that if I picked up a big block truck the mod list would be REALLY short which would=less running costs. Basically a nice exhuast, custom tune, and that is about it......'MAYBE' headers but I would have to find a set on the forums or e-bay or something. My main concern would be to increase MPG. If you consider the gains vs time/miles it would take to pay off certain mods it makes them a horrible value.

The diesel would require spending just to fix stupid issues like the PMD failures, upgraded cooling system on earlier trucks, etc.

15mpg is a goal worth shooting for IMO. (on BB trucks)
 

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Discussion Starter · #12 ·
454, no way I'd want a 3/4 ton w/ a small block.

Maybe it has a 3.73:1 for better freeway RPM. Just don't drive 80mph and expect 20mpg

Is there a 3.42 available for the 14 s/f, and the 9.25 IFS front?
For what I would use the truck for it would be a worth while swap.....(then again if figuring the cost/mpg increase ratio it probably wouldn't)

I have seen some guys with 2WD big block trucks with gear vendors that helped save MPG. But they are $$$ And I don't really know how/if that would work with a 4WD

65-70MPH max on highway. I'm convinced after noticing a few things with my Duramax that air resistance is the reason for the shitty mileage on the highway....
 

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Discussion Starter · #13 ·
step up to a NBS K2500 suburban :imo 6.0 >>>>>> 5.7 or 7.4

I wouldn't pit a 6L against a big block Vortec....And if I'm going to have shitty mileage I'd rather have more power.


Plus call me crazy but the 95-98 trucks are probably my second favorite trucks as far as appearance is concerned. (68-72 would be #1 I think)
 

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Well im pulling 10 MPG with my mods

Anyway i wouldnt ever buy a 3/4ton that was running a 350 in it
 

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HOT AIR BALLOON OWNER
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Believe me my first thought, was a 6.5 TD.....I miss the 'Max I had, and can't afford one again. But the 6.5 is no Duramax in power, and it doesn't have the best reliability record. I'd like to have a truck that I can take anywhere and not worry about getting stranded in a bad way..

The other reason I want to stray away from them is that if I picked up a big block truck the mod list would be REALLY short which would=less running costs. Basically a nice exhuast, custom tune, and that is about it......'MAYBE' headers but I would have to find a set on the forums or e-bay or something. My main concern would be to increase MPG. If you consider the gains vs time/miles it would take to pay off certain mods it makes them a horrible value.

The diesel would require spending just to fix stupid issues like the PMD failures, upgraded cooling system on earlier trucks, etc.

15mpg is a goal worth shooting for IMO. (on BB trucks)
I too am curious why the Dmax never made it into the 2500 Suburban. Ford did the 7.3 and 6L into the Excursion, great rides. Big mistake on GM's part.

Most 6.5s are pretty lame or mistreated, my boy has a '98 'Burb w/ the 6.5. Runs fine, all the factory updates, etc. Like you said, they need some help from the aftermarket to be reliable.

Full, properly sized, exhaust has always helped me gain fuel econ on rides and so has custom tuning.



Is there a 3.42 available for the 14 s/f, and the 9.25 IFS front?
For what I would use the truck for it would be a worth while swap.....(then again if figuring the cost/mpg increase ratio it probably wouldn't)

I have seen some guys with 2WD big block trucks with gear vendors that helped save MPG. But they are $$$ And I don't really know how/if that would work with a 4WD

65-70MPH max on highway. I'm convinced after noticing a few things with my Duramax that air resistance is the reason for the shitty mileage on the highway....
Yeah I've seen the 14B SF with 3.42:1 gears, so I would bet there has to be a matching set for the 9.25" IFS.

If you can do the labor, which I'm leaning toward you can, you may see some gains with the taller gearing. At least you know the motor won't be lugging itself too badly. But if you have 3.73:1 I would just leave it at that.



The factory piping is dual pipes that is 2-3/4" in many places.....As I understand it. Along with dual cats. I wouldn't consider that to big on a BB
Too much flow for the motor, another dude here put a single 3" on his 8.1L and picked up tons of midrange grunt. So the motor would be more efficient. I mean a single 3" has proven to flow more than enough to make 600rwhp easily.

I wonder how well/crappy those cats flow. I bet you could sell them for scrap and buy aftermarket high flows for the same price.
 

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Discussion Starter · #18 ·
I would be doing all the work myself....IMO when you buy old stuff like this it doesn't make economic sense to pay other people to do your wrenching.....Plus this isn't gonna be a DD so I'd actually welcome the project.

The 3.42's might be worth trying. But I don't really know what's involved in doing the front end....I guess I could just swap the rear gears for summer use and KEEP it in 2wd to test any kinds of gains.....At least that way if I didn't gain any MPG I could go back to the 3.73's for more grunt, and not have quite so much work. (a used but rebuilt LSD would be going in soon after getting it so I could do the swap then and see)

I want to do things that help increase MPG but all the work and money involved in a gear swap would have to show at least a couple MPG gain.

Anyone with any MPG numbers before and after a set of headers?

As for exhaust I'm OK going smaller. I was going to go that big because I still have the exhaust from cat back from my Duramax. But I don't even know if it will work without major modifications.


Some of the appearance things or things I think I could make use of will only hurt MPG so that sucks.....Prerunner type light bar up front, and a safari type rack on top (which we would actually use)
Might have to skip some of that stuff.
 

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Discussion Starter · #20 ·
I'm wondering how what kind a MPG a 383 Vortec in a 2500 suburban is capable of?

Summit Racing has some what I consider inexpensive 383's. 30 month 50,000 mile warranty, and plenty of power.... I wonder if highway cruising MPG would be better with this engine than with a bigblock?
 
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