I own a 1981 k5 blazer with a 305 and 350 turbo tran. the tran. needs to be replaced and i would like to replace the 305 for some better horse poweri would like to put a 350 and a 700r4 tran. will be driving offroad very often as i have a 3 mile long 4x4 driveway. would like to be able to pull trailers for work and still have fun offroad. I have 4.10 gears in it right now and a custom dual exhaust with two flowmaster mufflers.I have 31" x 10.5" mud tires on it right now and have gotten as low as 2mpg.

my question is what kind of gas millage can get with the 350 and 700r4 and what can i do to make it as econmical as possible.

 

probably wont change at all. the only way that 700r4 is going to benifet you is on the highway. but if youre just doing offroading and pulling trailers youre not gonna need over drive anyways.

there maybe other issues, i had a 6000lb suburban with a 400ci engine and 38s, that thing got 7mpg averaged out from the few times i checked and there was alot of offroad activity in there

 

will be driving on the pavement quite a bit. I have a 1 hour commute.

 

You have a NP203 transfer case correct?

Swapping in a NP208 or 241 would allow you to get rid of the auto locking hubs for some manual units, that should improve your mileage a little bit.

If you're getting 2mpg and driving an hour to work that's pretty impressive... Do you plan on running your 31's? if so you could benefit from an overdrive, those little tires and 4.10's probably have your 305 working overtime to keep it as highway speeds.

General mileage that I've heard with carbed motor and overdrive transmissions, assuming they are working properly, is 12-14mpg. That is for a stock rig with street tires. Lifted and mild off road tires drop the mileage to 10-12mpg.

Aggressive lift, tires and off road equipment shouldn't ever drop you below 8mpg, extreme cases might get to 6-7, but that's a hard core setup that shouldn't be run as a daily driver.

There are also TBI setups that get 14+ mpg.

Diesels get upwards of 20mpg.

 

i have an 85 k5 blazer, i bought it with a stock 305 (had an edelbrock carb) and standard 4 speed or 3 speed with granny gear whatever you wanna call it, and a 208 transfer case, it got horrible mileage i never calculated the MPG but it was scary going to the pump every week with a 30 gallon tank or 35 not sure, but anyways i dropped a decent 30 over 350 with a comp cams extreme 4x4 cam, summit stage 1 intake and a q-jet carb. lifted it 6 inches put 35's on it along with dual 3" exhaust and it gets great mileage now i haven't calculated it yet but im guessing proly around 12 to 14 mpg i can go a month on 1 tank verses 1 tank a week with the 305 so from that alone i believe a good healthy motor with a lil power can save you on gas but once you hook a trailer up to a gasser motor all bets are off they get thirsty quick with a heavy load