454 gas milage

[Jerry]

I have a 1987 motor home with a Chev. 454 motor (12000) miles. When we originaly purched this unit it ran bad (smoked, caughed and missed) The gas milage was in the high sixes at 55 mph with a boat on behind. We went through the complete tune up syndrome, plugs, plug wires, rebuilt carb, new a air cleaner, removed all smog pumps, new 10 ply tires at 110 ppi, distributor cap and rotor and set the timing about 2* advanced from factory spec. The RV runs great know and at 55mph with no boat it still get in the high sixes. The only thing I havent tried is putting on a couple of low restriction mufflers. Any ideas on improving the gas milage? THANKS Jerry

[Gumby]

Jerry, I'm pretty much in the same predicament. Have an '89 Dodge W100 (1/2 ton short box) 4x4 with a 318, and only get 9-11 mpg. I've had other 318's and all of them got at least 18 mpg. I don't understand why there is so much difference from those to this one. Please guys, help us out.

[Caleb]

I to have a 454. I get 6-7 mpg in town. But I have a Holley double pumper on it. I've been told that to improve the gas mileage a quadrajet carburetor would help greatly.

[tim(wi)]

You might want to try and replace your oxegen censors. Theye are not reguired to be replaced untill around 70,00 miles and you are not near that but it might be worth a try. New censors are worth %5 to %10 better gas milage. Hope this helps.

[Jerry]

Thanks for the advice but I don't think the older motors had oxygen sensors on them. Also mine rig has a quadrajet carb on it so I don't think that just changing the carb will help. THANKS JERRY

[Phil T.]

My 454 is of older vintage than yours, but the principles remain the same. First, the fuel mileage is dependent on the total load. It takes energy to move weight, and all the energy comes from the gas tank. Second, lighten up on the gas pedal. The torque of a big block is fun, but it costs $$ to accelerate. In town stop-and-go driving is where the small engines have a mileage advantage over the big ones. Last, know where your engine produces peak torque and peak horsepower. Buy a good tachometer, and drive according to the tach, the heck with the speedometer. My old 454 produces peak torque at 1600 rpm, peak hp at 2400 rpm. I drive it around 2200 rpm, and that's only 50 mph on the highway. Carrying a 2400+lb camper and pulling a 2500lb boat and trailer, I get about 8 or 9mpg on the highway. With just the camper in the box, no boat, it gets about 12mpg. The addition of low restriction mufflers may help, if you don't have a catalytic convertor. If you have a convertor, first replace it with a low restriction aftermarket unit. It's legal to do this if the truck has over 50,000 miles on it. My truck has no convertor, so I have changed the exhaust to a real dual exhaust, with full diameter pipes from the manifold to the tailpipe. I have a crossover between them located just behind the rear of the transmission to smooth out the exhaust noise, and it actually improves the torgue numbers. The "mufflers" are low restriction turbo models. This has reduced the underhood temperatures a lot. I have mud flaps with burn marks, but the heat under the hood is much more reasonable.