what gas mileage do you think I'll get - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ackattack · 05-01-2011, 11:34 AM

I'm seriously considering putting on a factory TBI system onto my 69 to help with gas mileage.

Currently it has a 600 cfm edelbrock.

It has 3.08 gears and a 4 speed. I'll be getting new tires sometime soon (probably go with 275/60/15) Right now it has 285/70/15 BFG radials t/a (they don't make that size anymore).

So take your guesses. I'm hoping for 18 on the highway, but we'll see.

I may buy a donor truck (88-93ish) with a 5 speed manual. With the 3.08s I think 5th gear would be 70+ anyways. With the current tires on it, 50 was at ~1500rpms.

.

Wrenchbender Ret · 05-01-2011, 12:29 PM

A lot will depend on the engine size.

Ackattack · 05-01-2011, 01:19 PM

Quote:

Originally Posted by Wrenchbender Ret

A lot will depend on the engine size.

Oh, its a stock 350

**Boog** · 05-01-2011, 03:23 PM

What kind of mileage does it get currently?

Ackattack · 05-01-2011, 04:03 PM

Quote:

Originally Posted by Boog

What kind of mileage does it get currently?

Don't know, I've had the truck for about 2 years now (jeese its been that long!!!!) and I've only ran maybe 3 full tanks through it. Plus it had a 4.10 geared Dana 60 in it.

**Boog** · 05-01-2011, 04:25 PM

Older 350/ 4 sp with 3.08 gear and 28" tire should get you 14 or 15 I think. That is a good gear and tire size for all around mpg in an older truck. An electric fan can add 1 mpg or so. That TBI setup could add 1 to 2 mpg as well. Unknown is the compression and cam in that old engine and how well it will work with the TBI setup. IMO you will have to go with OD to get near 18 with it.
I happen to know where there is a '97 5lt w/4l60E and harness complete. Made 19 in my 97 GMC excab with 3.42 gear.

**Palf70Step** · 05-01-2011, 12:35 PM

Probably 12-14 in townish driving. Maybe a little higher 15-17 for highway. If your easy on it.

Wrenchbender Ret · 05-01-2011, 03:50 PM

I drive a 70 stepside with 350 700R4 & 3.08 rear end. It has a Q-jet carb. I get 18 on the highway & about 15 combination. I was shooting for 20 but it just won't do it. I think with EFI & O-drive you could.

05-01-2011, 11:34 AM	#1
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,525	what gas mileage do you think I'll get I'm seriously considering putting on a factory TBI system onto my 69 to help with gas mileage. Currently it has a 600 cfm edelbrock. It has 3.08 gears and a 4 speed. I'll be getting new tires sometime soon (probably go with 275/60/15) Right now it has 285/70/15 BFG radials t/a (they don't make that size anymore). So take your guesses. I'm hoping for 18 on the highway, but we'll see. I may buy a donor truck (88-93ish) with a 5 speed manual. With the 3.08s I think 5th gear would be 70+ anyways. With the current tires on it, 50 was at ~1500rpms. . __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

05-01-2011, 12:29 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: what gas mileage do you think I'll get A lot will depend on the engine size.

05-01-2011, 03:23 PM	#4
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,663	Re: what gas mileage do you think I'll get What kind of mileage does it get currently? __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

05-01-2011, 04:25 PM	#6
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,663	Re: what gas mileage do you think I'll get Older 350/ 4 sp with 3.08 gear and 28" tire should get you 14 or 15 I think. That is a good gear and tire size for all around mpg in an older truck. An electric fan can add 1 mpg or so. That TBI setup could add 1 to 2 mpg as well. Unknown is the compression and cam in that old engine and how well it will work with the TBI setup. IMO you will have to go with OD to get near 18 with it. I happen to know where there is a '97 5lt w/4l60E and harness complete. Made 19 in my 97 GMC excab with 3.42 gear. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

05-01-2011, 12:35 PM	#7
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,471	Re: what gas mileage do you think I'll get Probably 12-14 in townish driving. Maybe a little higher 15-17 for highway. If your easy on it. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

05-01-2011, 03:50 PM	#8
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: what gas mileage do you think I'll get I drive a 70 stepside with 350 700R4 & 3.08 rear end. It has a Q-jet carb. I get 18 on the highway & about 15 combination. I was shooting for 20 but it just won't do it. I think with EFI & O-drive you could.

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