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Horrible mileage and not enough power

mountainexplorer

mountainexplorer

1/2 ton status
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Spokane, Wa./Ione, Wa
Say you had a stock 454, which only had a 625 Edelbrock Carb on it. Running great, timing right on. Turning 35's with 4.10 gears.

Highway mileage (towing a load or not) is about 5mpg. can tow and maintain speed just fine until reaching a certain grade steepness, then just bogs out even with it floored.

Nothing seems to be wrong, but for the lack of power and bad mileage, I shouldn't be getting that bad of mileage, should I?
 
I wouldn't try too hard to get much better, but you might try putting on a Rochester and see if it gets any better. My 72 has a 396/402 with a 750 edelbrock (1407), 35's, 4:10's, mild cam, and it gets about 5-6, whether it's towing anything, daily driving, whatever. Terrible gas mileage. My old man says that's good.
 
Have you checked all the easy stuff already?

4.10s and 35s without O/d is revving pretty hard for a big block IMO.
 
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Have you checked all the easy stuff already?

4.10s and 35s without O/d is revving pretty hard for a big block IMO.

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At 65 mph with a non-od trans 4.10's and 35's would rev to about 2500 rpm. That aint bad for a small or big block. Its not as good as having OD but the bigger tire with 4.10's are acting like an overdrive by traveling a farther distance per revolution that the tire makes.

Stepping up the ratio to 4.56 or higher would net more power at the loss of fuel economy. Conversely going down to a 3.73 or less would net better fuel economy at an expense of power.

Leaving the gears alone and look at the carb. That carb is small for a 454, but if its a stock or mild cam it would be enough. Any bigger and it would suck more fuel. That being said, is the existing carb jetted right for your application or is it as delivered out of the box? Did you pull the plugs to see if you are running rich or lean? Fuel economy boils down to optimizing the basics. Carb tuned up? Hows the ignintion system, plugs, wires, cap and rotor? What did you set your tires at for pressure? Air filter clean?

We got to be realistic here...a 454 crewcab is not the most aerodynamic beast on the planet, some barns have better. So you got a 6,000 pound beast shaped like a brick on 35's being pulled by a 454 with a carb. 5-6 mpg may not be far off if your rig is in top state of tune. If not tuned up, you might be able to squeeze more out of it. Maybe 1 to 1.5 mpg but don't expect to get over 7 in your combination.

Don't forget that having your rig up high on 35's is making your aerodynamics worse. Besides the air going up and over, its got to go under too. Your axles and undercarriage are not smooth and exert more drag at higher speeds. Thats why land speed record cars are low or any other green treehugger hybrid is low to the ground or also have belly pans to limit drag.

even moving to FI would not net you that much more MPG than the well tuned carb setup would. Don't get me wrong FI would help but you would still not hit 10 MPG with what you got. Check the basics and keep it in top tune.
 
5-6mpg is not all that bad IMHO. We have a 76' C30 dually with a stock 454 and we have managed 10mpg on it at 55mph but it gets about 7 or so average and it weighs considerably less than your 4wd CC and only has 31's. I would actually imagine a 795cfm stock 454 Q-jet would probably help you gain just a little mpg and make more power. /forums/images/graemlins/thinking.gif
 
Could be the lack of power is from the secondaries not opening.
 
I used to have 33's on it. I couldn't go over 60 without feeling I was reving it a bit too high. But then it would seemingly pull hills without slowing down (trailer in tow).

I put the 35's on it to knock down the gears some.

On my last trip, RPMs were just right. Just pulling some of the hills it seemed like if I had a gear between 3rd and 4th (its an SM465), it would have pulle dthe hill. 4th just wouldn't cut it (barely), and 3rd was just too low.
 
I get 10 with the same carb on my 350 with 38.5s. I never thought 10 was bad in a truck this big.

If you're in hilly terrain, I wouldn't say that's all that bad. Have you done a compression check, tune up, etc? Big blocks are known for flat cams, I'm sure that would seriously mess up your mileage. /forums/images/graemlins/smile.gif

Most of all, how are your driving habits?
 
I agree with everything you said.

I just last fall had problems with it because of a lack of maintenance on my part, but got it up and running good again. All the minor (tune-up) stuff shouldn't be the problem at this point.

I'm really not too disappointed about the 5mpg. Last I checked with the Q-jet on it I was getting about 7. Plus, like you said, a 1-ton 4x4 Crew cab isn't exactly lightweight or aerodynamic.

On top of that, I have every anti-aerodynamic device on the truck including a grille guard and winch hanging off the front, a bug deflector, 5 square lights up top, and a sun visor. Even on my way driving yesterday I thought to myself "If I was to try and be more economical, I'd pull off the light bar up top for this trip". But I didn't.

I'm mainly dissapointed in having to slow down and shift down to 3rd and go 35mph on the freeway up the pass. Just before hitting the hill I was bound and determined to stay in 4th. I switched over to my tank with premium in it, got up to about 70-72mph, hit the 1st part of the hill and "bluuuuhhhhhh".

All 4 barrels could be heard opening, as the fuel guage and speedometer dropped. I suppose I shouldn't be that dissapointed since I was towing an all-steel framed/bed 22' long trailer with a 2wd Dually Suburban with a 454/TH400 and FF14 bolt on it.

Maybe I'm just remembering the days of it on 33's. I guess I havent towed a whole lot with it since I got the 35's on it.

My Suburban, going up the hill out of Spokane with 4 of us in it towing another lifted 3/4 ton 4x4 Suburban on a trailer maintained above 55mph in 4th. It's a gas hog too. But I just love being able to keep up with little cars even when Im towing 3-4 times their weight. /forums/images/graemlins/grin.gif
 
I havent done a compression check. I thought a cam lobe was going flat last fall, but the 'ole Q-jet was just saying it needed help and it needed a tune up too. It just purs now.

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Most of all, how are your driving habits?

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Depends on how you'd classify them. /forums/images/graemlins/thinking.gif
 
With a trailer behind you it's hard to say if 5 mpg is bad though. Hell with 8k lbs behind my 350 powered 1 ton I struggle to get 8 mpg, but I hate trying to tow slowly unless it's unsafe to pull faster.
 
Can't really comment on the mileage, a 1 ton 4x4 with your accessories probably couldn't be more un-aerodynamic if you tried. My dads 454 K20 at about 6000lbs will get about 9-10MPG with Q-jet/454/465/Gear Vendors OD/4.10's and 32-33" tires on the freeway at about 60MPH. I think he gained about 1-2MPG with the OD unit.

As to power, with those gears I don't think you should be going that slow over a pass, if we are talking unloaded. His truck will pull Snoqualmie Pass at 35MPH, but thats towing a 10,000lb trailer. Empty, no problem doing the same at 70MPH. FWIW I think the gear vendor unit was essentially worthless...it doesn't allow you to split gears effectively, since the ratio is like .75:1...if it were .50:1 it would be much more useful. OD second trying to pull a hill still allows too much engine rpm and not enough speed.

This same 454 lost a cam lobe shortly after it's rebuild, and idle got noticeably bad, plus a backfire letting off the gas. Power still wasn't down TOO much, but he wasn't towing at the time.

For you to be losing that much power on a hill with your combo, I would think there is something very much wrong in your setup. Not sure what, but I wouldn't be satisifed if unloaded you can't go the speed you want anywhere.
 
On flat straight-a-ways, and only mild grades, I was able to go 65 mph smooth as ever with no power problems. With my trailer behind the crew cab, you sometimes can forget you are towing something. Until you get to a steep hill.

I think I just need to start building a good towing motor for it, so that by the time this one gives out, I can swap in the other one.

Hmmm... how 'bout a .030 over 454, flattops, open heads, RV cam (of specs to be decided upon)... that gets 20 mpg and can maintain 65mph up any hill towing my trailer fully loaded.

Oops, did I nod off and start dreaming again? /forums/images/graemlins/whistling.gif
 
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As to power, with those gears I don't think you should be going that slow over a pass, if we are talking unloaded. His truck will pull Snoqualmie Pass at 35MPH, but thats towing a 10,000lb trailer.

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On my way over the pass (westward), I was towing my 22' trailer empty... well, except for a truck cab on it... and I could maintain 55 and above fairly easily. (though I did have to open up all 4 barrels a couple times)

It was just coming back (east) towing the Suburban on the trailer that did it. If it was the trailer empty, I dont think it would have been a problem.
 
Must be it. I think I did get spoiled. I rode over with a friend to Portland, Or. 3 weeks ago towing my trailer with their '98 Dodge Cummins. Even though we didn't go over any passes, or have quite as heavy of a load, I could still get the "feel" of the difference in torque while riding in the Cummins.
 
They are just big hills. With more useable gears, and a better engine (no offense, I just feel newer engines are better in the power respect) it would probably be a different story, but unless you put a 6 speed in, and an engine that makes a million foot pounds of torque at the RPM's you are trying to pull at, they are always going to slow you down.

He's in the exact same boat as you it soudns like. I REALLY think a better transmission gear split would make a huge difference, but it's so costly and time consuming, it's not worth it just to "test" that theory.
 
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I REALLY think a better transmission gear split would make a huge difference

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Exactly what I was thinking when I was going back and forth between 3rd and 4th. Just wouldn't quite pull 4th, but had more than enough power in 3rd, just couldn't go much faster than 35 without over-reving it.

This motor has always been faithful, and runs really good, and never smokes or uses oil. But it's just a low compression, low HP motor that I agree can't keep up with some of the newer ones and how they're set up. I just like the fact that theres no computer and everything is easy and simple and direct. /forums/images/graemlins/smile.gif

In the words of Red Green (Canadian redneck TV show):

"Thats the problem with these newer cars... all this extra wiring... just more stuff to go wrong."
 
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Exactly what I was thinking when I was going back and forth between 3rd and 4th. Just wouldn't quite pull 4th, but had more than enough power in 3rd, just couldn't go much faster than 35 without over-reving it.

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I was running up Snoqualmie in 3rd around 45-50mph. My tach was up around 3000-3500 RPM though. Thats with a 350, SM465, 4.10 gears and 285/75R16 tires (about 33's). Just need one more gear to split 3-4 shift and I would be able to hold 60-70 mph loaded down. Of course you know how well my truck was loaded down... half of a Ford truck cut up for scrap in the bed with the cab I picked up from you on top of the bed /forums/images/graemlins/whistling.gif
3728Tr07.jpg


Do you have a tach on that truck?
 
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