gas mileage
 

Here's the deal, I want a big block in my 79 short bed I like the way it fills the engine bay up but I want to know what kind of gas mileage I can get? Here's the combo I'm looking to run, a carburated stock 396 or 454 a 700R4 and 308 gears what do you think it will get guys? And please just answer my question no flaming or dumb a$$ remarks.

Re: gas mileage
 

from what i have read you can not see past 12mpg in a big block period. i get about 10. but your truck is lighter so maybe u can see a bit better than 12. how tall of a tire with those 3:08's?

Re: gas mileage
 

I was thinking of putting 20" rims on her

Re: gas mileage
 

I suggest going with 3.42 gears. I think that it would let the motor be under less load, which could use less gas. Then again, I'm not sure on the difference between a SB and a BB.

Re: gas mileage
 

With the 700 and a 336 or a 342 gear you could get in the low teens. A 308 is too high in my opinion in overdrive. It all depends on the cam selection and the other specs of the big block. My TBI 454/400 only gets around 6\7 in town with short tires and a 308. I am pulling it out for a 5.3\4l60E combo. Jay

Re: gas mileage
 

yyuck yyuck iz a big block!!! no good gas milage!! yuck. oh sorry, no smart a$$...
11 keeping with trafic in town. 14hw....15/w/ the motor off rolling downhill (couldent help it) :D

Re: gas mileage
 

Why 342 gears? they'll make the engine work harder then 308's

Re: gas mileage
 

With an over drive the 3:42 gears are actually 2.39 in over drive the 308s are 2.15. The 342 will also help you come off the light a little easier. I usually like a 3:73 (2.61) with the overdrives, but with the torque of the big block you will be ok a little taller gear. Jay

Re: gas mileage
 

342s will keep the motor in a sweet spot where it will pull good in od and get good mileage 308s will just lugg it causing worse gas mileage and no power at all in od

Re: gas mileage
 

So what will the final ratio work out to with 20" rims and 308's. And can anyone tell me what the cruising RPM of a stock big block is at 75 MPH with a 700R4 and low gears like 342 or lower

Re: gas mileage
 

The size of the rim isn't what you really need to know, it's the over all size of the rear tires, that will tell what you need for gears. As for the big block thing, if your looking for milage your looking at the wrong engine!

Re: gas mileage
 

You didn't say what side tire you wanted just wheel, Assuming your stock tire is a 235/75/R15 which most 1/2 tons were. I figured using a 275/40R20 tire you get a final drive of around 2.16:1

Re: gas mileage
 

back when the '73 LWB was my daily driver I was getting about 7mpg. I was getting about 10 after a full tune up with a rebuilt HEI distributor and newer tires. My dad's old fuel injected 454 dually got about 10mpg

Re: gas mileage
 

My 1992 came with the 700r4, 4.3 tbi and 3.08 rear.

When it was new I got 25 mpg with a 500 pound motorcycle in an open bed.

If you want gas mileage with acceptable power I suggest you pull a 4.3 with the fancy fuel injection and the computer from a wrecked small S-10 Chevy Blazer.

Re: gas mileage
 

I get 13-14 on the highway...10-12 in town, warmer weather the in town improves a tad