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trucker40
12-17-2007 20:08:43
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Re: OT gas mileage problem in reply to BobOHIO, 12-17-2007 15:24:45
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After thinking about it some more-Skip said 15 mpg with a 69 3/4 ton with big gears.I had a 64 Chevelle With a 327 and it would get about 14 mpg with double hump heads,cant remember what horsepower that was,325 horsepower or more.I think the gears were 390 in that car.Thats been a long time ago,had L60 15 tires on back,drove everywhere 100+ miles per hour,4 speed transmission,headers,not much mufflers if any,dual point distributer.I know when I got that car I put new headers and Cherry Bomb mufflers on it and gas mileage got better,had high compression,burned ethel gas.That was in the early 70s,dont remember what all was done to motor or what cam,but I beat a 440 GTX with a automatic 2 out of 3 in the quarter mile.Had a 67 Chevy pickup with an inline 6 cylinder,top speed was about 80,think it was 456 gears.Got worse fuel mileage than Chevelle,it only had 1 or 2 barrel carb,Chevelle had 4 barrel Holley.I had a 72 Buick with a 2 barrel Rochester carb, 350 and it got worse gas mileage than the Chevelle about 10.Quadrajets did seem to get a little better mileage than a 2 barrel if you kept your foot out of it.Holleys were better if you kept your foot out of it,than Quadrajets overall because a wore out quadrajet will guzzle gas. The older cars had bigger valves,little if any smog stuff,way more horsepower,and if you carefully pick your parts,with new technology heads,cam,carb,trans,and with more power Higher rear end gears,to an extent,you could get lots better mileage.If you just kind of slap some parts together,it could be worse gas mileage. My guess is its a cam like a RV cam,with roller lifters,a little hotter than stock,or some Z 28 cam.You want power,but you dont want to run stock car races with a front wheel off the ground either.I say roller lifters because what you can do to cut friction in cam area means it winds up quicker,getting to shift sooner.Thats just kind of a drivability thing cause all these new little cars scream away from a stop lite.Less friction equals better driveability,more mpg. I dont remember much more(getting old)but the trick is in how much power you have for the gas you put in.If you can get 350 horsepower out of 350 cubic inches means when you are driving down the road 100+ mph,your foot is not as close to the floor on the gas pedal than if you have a 350 ci motor 170 hp.Foot not as close to floor=better gas milage.Sort of how my cave man mechanical brain thinks. If your mechanical advance is stuck,or even dont swing fast enough,it wont have any power.That cuts your total timing by a bunch,which if its supposed to have 170,now it may be 120 horsepower or less.That would have to hurt the heck out of fuel mileage. I think I remember,but may be wrong,that if those weights are stuck it will be real doggy,kind of buck and spit,especially if its cold.If nobody thought to check them might have been that way a long time,even since you rebuilt it. I enjoyed trying to answer your question,thought I had forgot all that stuff,but I see I didnt forget everything I learned trying to make a living as a mechanic years ago. I drove an old gas burning dump truck for the county for a while.All of them were alike,late 70s chevys with same size bed,same tires,everything.I didnt allways drive the same truck,some of them would haul 7 loads a day,some 6 to the same place.If I was driving the blue one I would pass the others,if sombody else drove it they would pass the rest of us.With everything the same,I think it had to be higher geared.The way I see it,if you start your car,drive to your destination,and it takes 10 minutes you shut it off.You change your gear ratio,it now takes 9 minutes,and you dont drive over the speed limit either way,you are saving fuel,Thats why overdrive gears get better fuel mileage. A lot depends on what you do with a vehicle.If you just barely can pull what you are trying to pull,lower gears could help fuel mileage.If your gear is so high you have to downshift to pull hills on the interstate,you could have bad fuel mileage,need lower gears.If you are strainin to do the speed limit winding out your motor all the time,bad gas mileage,need higher gears. If after all this,mileage is still bad,push clutch in and coast everywhere you can,see if you can get people to tow you whenever possible,with 3 dollar a gallon gas you need all the help you can get.
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