armyvet8492

hey guys, i got this 84 c-10 silverado. it was a deisle but has been swaped to a 86' 350 and rebuilt,and has an elderbrock 4bbrl on it. it runs great but gets somewhere around 10 mpg or less. its a nice truck and id like to keep it. does anyone have some ideas on intakes and maybe a 2bbrl carb set up that might help? what about the rear end gearing?....thanks

therewolf

Hi armyvet8492,

Welcome to the Chevy Forums.

You need to find your current gear ratio before considering a change.
For Gearing RPOs, search "gear ratio".

I've been happy with my shift to 342s. Admittedly a little doggy on pickup for most, but the highway cruising revs are schweet!

tinbender59

84??? that looks like a 94? if it is an Overdrive truck, and you have a three speed that could be a psrt of it, also as stated befor check your gear ratio, it may have 3.23 or some thing crazzy like that since the diesel only turned arround 3500 max rpm

armyvet8492

no its the red one in the background, and yes it has the overdrive tranny, i did some research and i think the rear end is like a 308? or somewhere near that. so would i be better off getting a rear end from a junk yard? and what year trucks should i look for? that will work without major changes? and what about tha tranny?....thanks for all the help....

mwy123

Look in your glove box for the sticker with all the factory options on it. Being a former diesel, it could have had anything from a 3:08 to a 4:56 in it. The 4:56 would by unlikely unless it was a military truck. If it has the O.D then it probably came with either a 3.42 or a 3.73, you cant lug a diesel so you gotta keep the RPMS up. The easiest thing to start with is a tune up. Plugs, wires, and air filter. You can swap your edelbrock for a quadrajet and keep your foot out of the 4-bbl. The front two barrels of a quadrajet are smaller than the barrels of a 2-bbl.

In another direction, you didnt say if the engine has had any internal modifications done to it, specifically the camshaft. It it has a bigger cam installed there might lie your problem. The cam has to work with your intake, carb, rear end gears, and torque converter.

If you have big tires on your truck that will make a difference too. Big tires means its riding higher up in the air, every inch up means one less MPG.

Fuel mileage can be very frustrating, I stopped driving my first truck on account of it. Swapped a TBI 350 for a 2 bbl 305, outed a 5-speed for a TH400 and swapped gears to 2.73, 12 MPG was all it got, and to this day I still cant figure out why. Keep at it and you can figure it out.

therewolf

In any event, be certain of your gear ratio before you start thinking about swapping them out.

Find your RPO code for your gears on your "Service Parts Identification" sticker inside your glovebox. You really want to be sure, out the door a gear swap is about 2000$. Because for that money, you'll be PISSED if you find out that you just traded those gears for say, a set of 323s, and it turns out they were 323s to begin with...

armyvet8492

ok as far as we know the 350 was rebuilt stock no high preformance mods,it has the elderbrock 600 and the 4 speed auto trans. i just got it the way it is. i have done all the plugs,wires,dist,rotor button and put mobil 1 in and also did a trans flush and did a rear diff flush,i just put 22's on it. so if i was to put the stock 15's that would be better? if so i will do that first before getting into changing anything else for now..as far as finding out the gear ratio i dont have anything in my glovebox(stickers) or on the doors there all missing.....thanks again for all the help

mwy123

Do you have a tachometer? If you dont, try running a tank of gas in Drive instead of OverDrive and see if your mileage changes.

tinbender59

there is another way to check gear ratio. jack it up put it on jack stands, crawl under, put a chalk mark on the drive shaft where you can see it. Then mark both back wheels, this will take at least 2 people. Put the truck in neutral, turn both wheels one full revolution the same direction, while counting the revolutions on the drive shaft. the partial turn at the last should be straight forward as far as % of revolution. good luck!!

armyvet8492

ok thanks,,we did a flush on the tranny and its a three speed not a od tranny.and found the vacumn line to the modulator was sucking air and not letting the trans shift properly so fixed that and the trans is smooth shifting through all the gears. and would i be better off putting the 15's back on? and can anyone tell me how to maybe tune the carb alittle better. its a elderbrock 4brl i think a 600,,,thanks