3.42 to 2.73 Gas Mileage!

[crazychevydave350]

I have a 1982 2wd with a 305 Engine, A th-350 and  4bl Carb. I Currently have a 3.42 gear ratio and I  am considering swapping to a 2.73 Gear ratio.  Anyone have any idea what kind of mileage difference there would be? Would it be worth it?  I am assuming at 60 mph on the highway.  Right now I am running about 2400 Rpm at 60. The truck is not a posi and has a open carrier. Wanting to switch to a posi at the same time.


Any Help would be appreciated thanks

[roadrage41]

I can tell you our shop beater s10 has 2.73s in it with a 700r4, gets good mileage, but along borders on being worthless as a truck. Its a 3.8 though.

[Blazin]

I had a 84 K 10 with 2:73s, SM 465, and a 283. It got about 22 MPG on the highway no lie. around town etc it was about 15 MPG. More than once at 50 or MPH I would be driving along, and all of a sudden realize, oh wait I have another gear!

[velojym]

I had a 84 K 10 with 2:73s, SM 465, and a 283. It got about 22 MPG on the highway no lie. around town etc it was about 15 MPG. More than once at 50 or MPH I would be driving along, and all of a sudden realize, oh wait I have another gear!

Wow. That's about what I get with my 05 Trailblazer. *sigh*

[autorepr]

What kind of driving do you mostly do with it?   I had a 85 3/4 ton with a 350, T400 and 14 bolt with a 4.11 gear and it got good mileadge if I just drove it in the city. I could take off from a stop at an idle and barely push on the gas to get to 35MPH keeping your RPM low getting up to speed and not alot of RPM to maintain the 35MPH. (grandpa style driving) The city was mainly all I drove that truck in.  On the highway.......forget about it!    If you go to high of a gear with a low power 305 the truck will struggle getting going and use more fuel cuz you'll have to stay in the throttle for take off. I had an 80 Malibu with a 3.8 and T200 with a 2.73 and that thing was horrible on take off. I swapped in a 350 and T350 and it actually improved. (again Grandpa style driving)

I'd keep the 3.42 and get a 700 with OD. Corse that's gonna cost a little more.

[mats1985gmc]

look into an overdrive. there are lots out there and you can keep your gears. I had a stock 305 with 308 gears and it was a DOG. decent milage. I now changed the motor and tranny and gears. 373 gears and a 700r4. very good highway set up and rips the tires off. Just  a though

[crazychevydave350]

I mostly drive it to work, in town less then 2 miles. I have had the truck 2 years I haven't needed to pull anything yet. On occasion I do haul stuff in the bed. On the highway I almost never drive over 55 mph. And getting right around 10-11mpg. I have been thinking about putting in a 700r4 too, and that seems what most of you are recommending. Only problem is that the truck is worth only about $1000-$1200. Even though the engine, trans, and rear are all pretty fresh, also it has a previously salvaged title. Do I dare drop another grand in it? With only a 305?  Should I try to sell the truck, take the money and save a little more and get a Fuel Injected truck with a 350/700r4 already installed?  Would that make more sense???

Thoughts and concerns are appreciated!

Thanks for previous replies too!

Dave

[VileZambonie]

Put a 700R4 in it.

[eventhorizon66]

I mostly drive it to work, in town less then 2 miles.

It seems that much of your commute is done with the choke in operation, so it will pay to have this set up perfectly.

[Grim 82]

Put a 700R4 in it.

Agreed. The lower first gear will make it feel like it has more take-off power, and your cruising rpm's will drop significantly.

[Lt.Del]

autorepr is correct.  City driving, a 305 w/ a tall gear will require a mashed accelerator the whole time.   MPG will decrease unless you drive on the highway a lot.

Vile has a great idea, as always, a lower geared trans that has Overdrive for highway speeds.

[Irish_Alley]

A locked posi will also decrease MPG due to having to turn more. Also what MPGs are you having now. A change in driving can get you at least 2 with no problem

[snibook7537]

Blazin your the man I gotta say.  I love my SM465 and I always see you posting about plowing with it and then 22MPG I know thats mostly in the Diff gears but Wow. I would love to have half the trucks you ever had. I have one now and had one before that with sm465's I loved them all. Good to hear that somebody doesn't just want an auto in a full size truck, just wish they would bring them back in the new bodystyle.

[Laderhosen]

If your commute is less than 2 miles why are you fussed about gas mileage??? How long would it take you to make the money back if you swap the gearbox or rear end gears??? I'm in the same predicament, I keep thinking I should convert my Blazer to LPG, but for same price as an LPG kit I can buy a lot of gasoline!!!

Also I've got 3.08 gears on my Blazer with a 700R4 and it drives horrible. My truck should have 3.42 gears so I've just ordered a 3.42 ring and pinion set. The gearbox seems to hold the gears too long, especially when cold.

[zieg85]

I had a 84 K 10 with 2:73s, SM 465, and a 283. It got about 22 MPG on the highway no lie. around town etc it was about 15 MPG. More than once at 50 or MPH I would be driving along, and all of a sudden realize, oh wait I have another gear!

I think that combo is about perfect IMO.  My 85 C20 has the tall LT235 85R16 with the 3.21 while not as high geared still gets 16 with the 454 if I keep it around 60 mph and not lacking any power... My $.02