Fuel mileage

[one9six9]

I know that this is a topic that I shouldn't be conserned with, but with the price of gas I am very curious.
I have a 69 with an I6, three speed auto, and a 308 rear end. What can I expect for highway RPM, and all around fuel consumption? I will have 255/70 tires on the truck too.
I know not to expect much, but with the I6 I was looking for at least 15 mpg city. Is this realistic? I hate to think that I was building a truck that I will not be able to afford to drive.

Thanks,
Keith

[jgrh64]

not sure but you can put a 200R4 OD trans in it they are cheaper than the bigger 700R4's and will hold up well behind a 6 this will really help

[one9six9]

What is the average cost of on of the OD trannies?

Keith

[dave2953]

I"ve seen them rebuilt for $1,000-1,200, but I don't know if that's a good price or not. As far as the gas mileage goes, you may be able to get that if it's set up right. I have a 305 w/ a PG and 3.73 gears and get 13 mpg but I rarely ever break 50 mph.

[sb69chevy]

Not sure what gears I have out back, but w/ the 350 and PG I get about 13-14 mpg w/ about 65-70% highway driving. Tach turns around 2800 @ 60 mph.

[72BLUZ]

You Should Get The Mileage You Wont. I Have A 350/350 With The Same Tire Size. I Averaged 14 Mpg Going To Maggie Valley For The Truck Show

[Longhorn Man]

with the 3.07 gear, you'll be revin about 2500 on the freeway at 65.
An overdrive with that gear ratio would bog the engine down, a 3.73 would be a better ratio for an overdrive
even so, that'll only drop your cruise RPM down a little, 2100 - 2200 IIRC
the average on these trucks is 10 - 12. Obviously, some will do better, but plan on 10 to 12 and be thrilled if you do better.

[whitelightenin69]

I would kill to get 13-14 mpg I only get about 8 mpg with 350/400 3.73 gears and 275/60 tires. I am in the process of putting in a 700r4 so I can afford to drive more than 1 time a week.

[GREASEMONKEY72]

350/350, 3.07, 31's and i get about 8mpg city

[rough69]

I don't even want to know...

With the same combination my C10 has, my old El Camino used to get 8MPG (350 / TH350)

I think it has a lot to do with driver style / habits, me personally I have a VERY HARD TIME staying out of the throttle.

[prairewolf]

I just started measuring in FPG (feet per gallon ) i get about 42,240 .
it seems like a lot of feet so i am ok with it.

[jgrh64]

rebuilt around me is about $895 .If you use have a 250 cu in 6 go to a 194 cu in head, headers and a better intake- carb it will be more efficient have more torque and run great with the higher overdrive. I'm surprised you don't have a numerically higher gear with a factory 6

[one9six9]

Originally Posted by jgrh64

rebuilt around me is about $895 .If you use have a 250 cu in 6 go to a 194 cu in head, headers and a better intake- carb it will be more efficient have more torque and run great with the higher overdrive. I'm surprised you don't have a numerically higher gear with a factory 6

I may have a numerically higher gear from the factory, but I am converting it over to a disc/drum with a crossmember found on a 72. I also pulled the rearend so I would have 5 lug all the way around. We checked the marking on the rearend and it states that it is the 307 or 308. I don't remember which exactly.
I was told to look for at least a 308 so the engine wouldn't be working too hard at highway speeds since I have a 3-speed auto.
Maybe one day after everything else is done I will look for a more modern engine to drop into it. I think a 4.3 litre would be a great engine for an upgrade, but anything like that would be at least a year down the line.

Keith

[jgrh64]

4.3 is a small block Chevy with two cyl cut off uses allot of same parts very good engine but don't short change your straight six ,check inliners international to see the potential your motor has.

[snj8198]

I've been getting 13 on the highway and 10 in town if I keep my foot out of it.