1985 gmc swb 305/700R MPG - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Firebirdjones · 02-10-2016, 08:33 AM

I'd say there is a lot more MPG to be had with that combo. Likely need to go over things in the tune, dial in the AFR, check tires, brakes etc...
30" tires and 3.08's isn't bad. I had an 84 blazer with that exact combo with a goodwrench 350 in it straight out of the crate, it got 16-17 MPG regularly.
My 72 blazer with a 6.0 LQ4, 4L60E and 33" tires with 3.07 gears go 22 mpg on highway trips. I added 3.73's and highway dropped to 20 mpg.
My 79 1 ton with a 454/400 turbo and 3.73 gears just tickles 14 mpg on the highway with it's stock 16.5x9.5 tires (I think 31" tall) and that's with no overdrive.
If my 454 can do that I see no reason your small block couldn't do better.

02-10-2016, 08:33 AM	#7
Firebirdjones Registered User Join Date: Oct 2009 Location: Prescott, Arizona Posts: 2,396	Re: 1985 gmc swb 305/700R MPG I'd say there is a lot more MPG to be had with that combo. Likely need to go over things in the tune, dial in the AFR, check tires, brakes etc... 30" tires and 3.08's isn't bad. I had an 84 blazer with that exact combo with a goodwrench 350 in it straight out of the crate, it got 16-17 MPG regularly. My 72 blazer with a 6.0 LQ4, 4L60E and 33" tires with 3.07 gears go 22 mpg on highway trips. I added 3.73's and highway dropped to 20 mpg. My 79 1 ton with a 454/400 turbo and 3.73 gears just tickles 14 mpg on the highway with it's stock 16.5x9.5 tires (I think 31" tall) and that's with no overdrive. If my 454 can do that I see no reason your small block couldn't do better.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.