454 dually gas mileage ?

[zieg85]

OK, mine is not a dually or is the carb 100% as it is original untouched...  I check my mileage every time I fill up.  My 85 with the 8600GVW in my signature below is as close to a 1 ton as you can get with 2 less wheels and extra wind resistance you get from the dually fenders.  Everyone thinks I am telling a lie with my mileage but I get a solid 12 mostly country driving.  On the interstate that bumps up to 14.5.  When the carb was right my best mileage was 15.8 with the tailgate down on my first trip home with it about 5 years ago when it had a little over 123K on it.  Heaviest load was pulling a 35 foot 5th wheel which made it 10 mpg.  Never had a problem with my gearing towing anything I have tried.  I get it rolling in low and shift to first ASAP.  I do know when I exceed 65 the mileage goes down which leads my to believe your gearing is your low MPG.    My $.02

[Mr Diesel]

I would check the fuel pump pressure. If someone has switched to an electric pump it might be too big and overfueling the carb, or if it is mounted under the hood it might not be pushing enough psi. Some pumps do not work well under the hood pulling the fuel, but rather near the tank pushing it. Also, sometimes underhood temps are too hot for an electric to survive. Often the pumps have a psi rating labeled on them, but I would put a guage on it to see what it is actually doing. I think most Edelbrocks do best on about 5.5 psi @ idle. Not sure if that is the same for the 750cfm models. I'm sure there is a technical .pdf available on their website.

[mountaindrew]

OK, mine is not a dually or is the carb 100% as it is original untouched...  I check my mileage every time I fill up.  My 85 with the 8600GVW in my signature below is as close to a 1 ton as you can get with 2 less wheels and extra wind resistance you get from the dually fenders.  Everyone thinks I am telling a lie with my mileage but I get a solid 12 mostly country driving.  On the interstate that bumps up to 14.5.  When the carb was right my best mileage was 15.8 with the tailgate down on my first trip home with it about 5 years ago when it had a little over 123K on it.  Heaviest load was pulling a 35 foot 5th wheel which made it 10 mpg.  Never had a problem with my gearing towing anything I have tried.  I get it rolling in low and shift to first ASAP.  I do know when I exceed 65 the mileage goes down which leads my to believe your gearing is your low MPG.    My $.02

That's awesome man!  I have an 86' 8600gvw c6p 454 HEAVY duty SRW just like yours and I have bested at 12.3 mpg @ 55mph with a little bit of running around in the city.  Mostly I drive dirt backroads at 30-35 mph, stop and go, and get 10 to 10.5 mpg.  I have 3.73s.  What have you got? 

[VileZambonie]

I would check the fuel pump pressure. If someone has switched to an electric pump it might be too big and overfueling the carb, or if it is mounted under the hood it might not be pushing enough psi. Some pumps do not work well under the hood pulling the fuel, but rather near the tank pushing it. Also, sometimes underhood temps are too hot for an electric to survive. Often the pumps have a psi rating labeled on them, but I would put a guage on it to see what it is actually doing. I think most Edelbrocks do best on about 5.5 psi @ idle. Not sure if that is the same for the 750cfm models. I'm sure there is a technical .pdf available on their website.

That was 5 years ago and this guy is long gone so I doubt he'll get your advice.

[Mr Diesel]

Duh. I only checked the date on the most recent post. Got me good this time.

[zieg85]

I vote to have the search function disabled so this can't happen again. 

[VileZambonie]

Nah, it's good to see good info & discussions and nothing wrong with bringing a post back from the dead if you can add to it. I'm just pointing out if you're giving advice to the OP that he's long gone.

[malibu795]

i ran a 84 dually rclb withn 454/400 750 carb headers 2.5" dually exhaust and ignition landed 13-14 on the freeway runing 65-70 with 235/85/16 and 4.10 gears

[Captkaos]

The forum warns you before you post to an old topic.