454 dually gas mileage ?

[truck1974]

I recently bought a 1979 3+3 4dr 4x4 dually.  It has a 454, 4.10's and a 4spd manual sm465 transmission.  The motor was apparently rebuilt 7000 miles ago.  Apparently a stock rebuild .040 over.  The engine doesen't seem to like over 3500 rpm's and I took it to pull my race car, maybe 5500 lbs including the trailer.  Was getting about 5 miles per gallon.

Now I know these trucks / engines aren't made for fuel economy but 5 miles per gallon sucks.  I was hoping for close to 10.  Or at least 10 empty.  What could I do to increase the fuel economy.  It also has a newer 750 edelbrock carb and dual exhaust with glasspacks. (that's the way I bought it).  Is that the norm for these trucks (5 mpg)  mileage wise?  

Matt

[roundedline]

Typically they get about 9 MAX regardless of what is behind them, and that usually highway mileage.  The carb may be out of adjustment and may one of the things killing the mileage.  Especially if it isn't tuned up.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[truck1974]

Carb is tuned properly by someone I know and have faith in.  Something else?

[stepside454]

If i wanted MPG Id go back to a Q-jet

[roundedline]

Ditto, if it isn't the Edelbrock Q-jet, then that will be a possible solution also.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[truck1974]

Thanks guys.  What does one normally see for milage with a rebuilt and properly tuned quadrajet?  Maybe 9 mpg at best?

[RSBAD454]

You bought a 454, noway in heck your Mileage will improve. You have a heavy truck and haul heavy loads period. You should buy a newer diesel that gets about 17+MPG chipped hauling loads. I'm not being mean, but what did you think you were going to get for mileage?

Toys are my game

[truck1974]

I dont haul "Heavy loads" as you stated.  5000 lbs is not a "heavy load" last time I checked.  Yes it's a 454 but it should get better than 5 miles to the gallon even if it is a heavy truck.  If I had money for a new diesel I would have bought one buddy.

[ChevyGuy]

One thing that I can tell you that is killing a point for milage is those glass packs.... better off with turbo mufflers. Also size of the pipes probally need atleast 2.5. Small things always help like carb tuning and better spark. Also you said it has the 4 speed thats another big deal on milage.... switch to a auto helped my heap.... I would consider a th400. You said the engine doesnt like over 3500.... sounds like timing needs work or the distributor isnt advancing which could lead to milage issues.

[roundedline]

A manual will get better mileage than an auto for every application.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[DnStClr]

Years ago I had a 79 Suburban with a similar setup, but with an auto tranny, and headers. It got 9 mpg empty and 7 mpg pulling a 27 foot travel trailer that weighed @8000 lbs. You're right- 5mpg is crummy.
What kind of air cleaner do you have on it? A high performance one will help. (You pro'lly know that since you race- dumb me)
Another help might be a fuel pump upgrade if you think the engine is starving for gas. Any time the engine is not getting enough gas, it's going to bog down, run hot, get poor gas mileage, etc.
A 3rd suggestion is to add a carb spacer under the carb to help atomize the fuel better and give you more mid-range power.

[truck1974]

Well, I do race but I'm no expert and always like to hear other's ideas.  The air cleaner is an open element type, but not a K and N high dollar unit.  There is no carb spacer.  One thing I don't care for is it has an electric fuel pump.  I don't know why they just blocked the manual fuel pump and ran an electric?  I dont have anything against electric pumps but I've only had a manual pump go bad once, and there easy enough to change.  

I'm not looking for 15 mpg here I was just hpoing for 8-9 maybe 10 at best which shouldn't be a miracle to ask for.   Remember when your only getting 5 mpg even 7 is a huge increase.

Matt  

[roundedline]

What kind of edelbrock carb is it?  Thermoquad version or the Q-jet version?  The Q-jet will be better on gas due to the smaller primaries.

There are a ton of variables, but here are some things I would check:

Have you checked/changed the plugs? What do they look like? Plug wires?  Distributor cap/rotor?  Basically have you done a tune up on the truck when you got it (or recently).

Is the clutch in good condition? (not slipping)
What air pressure are you running?   Low pressure will degrade gas mileage.  What about alignment?, brakes?  I am in no way saying to replace these or they are the exact reason.  What type of driving are you doing?  Highway, stop/go?  What speed?  

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[DnStClr]

Here's what I think- (fwiw)When we think of an engine as an air pump, which is basically what it is, we have to remember that the more air we can throw into it, the more efficiently the engine can use that gas the fuel pump is supplying it with. That's why one of the 1st places to start is usually the air intake and cleaner. There has to be a balance of air in and air exhausted.  The electric fuel pump is supplying a constant supply at higher pressure for you, and now you gotta do it a favor and give it some air to work with. It sounds like you've taken care of the tune-up.

[87454westernhauler]

we had one exactly the same year and drive train, if you set the carb. so that it barely ideals it will increase on millage a little. don't run it over 3500 RPMs, the best we ever got with it was about 9 and that was not often. but we have a newer one now, an 87 fuel injected with glass packs and headers and we are searisly getting over 15 MPG after i just put new wires and plugs in it. if you run it about 2500 in 4th gear it will get better milage too. the headers help a lot!!