Gas Millage (9mpg ???) === I know its been beat to death but im lost here

[withoutfear33]

i have a 1995 chevy silverado with a 9in lift but its only on 35s right now.. i finally decided to check my fuel millage out because it has been getting worse. the spedo is right on it as is the odometer. and yesterday i ran a full tank out and it got 212 miles to a tank and i caculated it also to how much i put it back in it to fill up and either way i go about it its only getting 9 miles to a gallon... i mean thats horrible (my 96 gets 17 all day long and has a 6in on 35s) i recently had tranny rebuilt and changed all fluids in the truck and i also changed plugs..

it has factory gears but so does my buddys 95 on 35s and hes getting 15 mpg... what am i doing wrong here.. it travles good down the road nice and smooth also.. it does how ever have stright pipes on it would putting a muffler on it correct this problem any by creating more back pressure?


any ideas on what to do?

 

[dale_gribble]

I see that you note it is a 355, so it obviously isn't stock. Tell us about the engine mods. I think mufflers is a good idea for back pressure for sure, if not just to be nice to your neighbors.

 

[withoutfear33]

I see that you note it is a 355, so it obviously isn't stock. Tell us about the engine mods. I think mufflers is a good idea for back pressure for sure, if not just to be nice to your neighbors.

its actually all stock minus being punched .30 over and having the heads ported to flow a lil better, nothing crazy at all and actually it doesnt feel any more powerful then a stock 350.

 

[DieselPower]

How do you drive? My last 355 had a 700R4 behind it with 3.7 gears. Driven hard, 9 mpg was not difficult to do. Driven easy, 22 mpg was possible. You have the aerodynamics of a brick sh*thouse, quite a bit of weight and a lot of rolling resistance. You'll want to pretend you have a raw egg between your foot and the gas pedal in order to keep the acceleration to an economical level. If you step on that pedal much at all, 9 mpg is probably doing well. You may be making the straight pipes sing too much! Also - consider checking the compression. There may be a problem.

 

[withoutfear33]

How do you drive? My last 355 had a 700R4 behind it with 3.7 gears. Driven hard, 9 mpg was not difficult to do. Driven easy, 22 mpg was possible. You have the aerodynamics of a brick sh*thouse, quite a bit of weight and a lot of rolling resistance. You'll want to pretend you have a raw egg between your foot and the gas pedal in order to keep the acceleration to an economical level. If you step on that pedal much at all, 9 mpg is probably doing well. You may be making the straight pipes sing too much! Also - consider checking the compression. There may be a problem.

i drive as easy as i can because im tired of filling the junk up lol... i think i may have a problem ive never payed much attention to it until today on lunch at idle it does have a miss and when you let off the brake and let it take off its self insted of pushing on the gas it kinda studders and shakes then when you hit the gas it clears out and drives like nothing is wrong.. plug wires, cap and rotor may help me..

 

[Tony_SS]

I can't get better than 13.5 mpg no matter how I drive, so 17 would be a dream for me!

 

[DieselPower]

You had it bored as part of a rebuild, if the rings didn't seat well, you'd have poor compression, less power - and lousy mileage. Check the plugs for color - make sure they have a decent color to them. Verify that the air cleaner is able to flow air... Got headers? Check the wires for burn-through. The Chevy head design sucks as it puts headers too close to the wires and high temp wires and shielding are often necessary. I'm reaching here - I've always gotten reasonable performance and economy out of my SBCs.

 

[MOBS]

Dual straights on my stock 350 increased hwy mpg....never checked for city, it's always on the hwy. I have a 357 sitting at 10.5cr that doesn't get near that bad mpg, so I'd suggest doing a full tune-up and also like DieselPower stated, check your airflow and your compression numbers on each cylinder.

 

[withoutfear33]

OK ILL BE DOING A FULL TUNE UP TONIGHT, I DONT HAVE A COMPRESSION GAUGE BUT IM GOING TO A PARTS STORE TO SEE IF I CAN FIND ONE.. WHEN I CHANGED PLUGS I DIDNT SEE ANYTHING UNNORMAL BUT THEN AGAIN I WAS NOT LOOKING TO FIND ANYTHING EITHER. ILL CHECK THEM OUT TONIGHT. I ALSO HAVE NOTICED THAT WHEN THE TRUCK IT HOT IT WILL FIRE RIGHT UP NO PROBLEM BUT WHEN ITS COLD AND AROUND 30 AND BELOW THE TRUCK HAS TO CRANK A FEW TIMES BEFORE IT STARTS.. IS THIS A SIGN OF ANYTHING THAT COULD BE MY PROBLEM?

 

[Tempted]

Eh I get about the same. Normally I am towing and get around 8mpg. Not towing, 10 or so. And its just a 2wd reg/short on 31x10.50/15 with a 3.42 rear.