straight six question

[AJNapierski]

I have been considering putting a six and a 4 speed in my truck what I am wondering is what kind of mpg I could get out of it with that set up, its a 2wd shorty and I will be running 308 gears if that helps. Thanks in advance

[Sharps40]

I'm runnin a 65 SBSS. 1971 Olds Rocket 250 I6. Currently running the peanut 3 speed and 3.73 rear. With the weber 2 barrel and the HEI ignition I pull an honest 18.4 mpg combined hwy/city every tank. Ocassionally 19.5 to almost 20 on the interstate staying at or below 65 mph.

Switching to a 5 speed this winter, expecting to see an additional 2 to 5 mpg.

308 might be a bit much for a six....pretty slow start but prolly great on highway...your final drive should still be 1 to 1 just like the peanut. (Mr. Langdon does not recommend less than about 3.50 rear gear with an overdrive manual gear box...so I'm stickin with my 3.73 out back.)

[Lugnutz65]

Originally Posted by AJNapierski

I have been considering putting a six and a 4 speed in my truck what I am wondering is what kind of mpg I could get out of it with that set up, its a 2wd shorty and I will be running 308 gears if that helps. Thanks in advance

Read Post #362 on this thread. Look at earlier threads too and you can see his pictures of the installation and carb tuning. Sharps40 says he's getting 18mpg with a 250ci and a correctly tuned Weber 32/36 carb, a 3.73 rear and a 3 speed factory tranny (which is 1:1 final gear like the 4 speed you're contemplating). You thinking about a Super T10?

If you use a Rochester B carb, an inline 230 or 250 and 3.08 gears I'd guess you'll get 15mpg or a tad better depending on how you drive and if any is highway or not.

EDIT: Looks like he beat me to the punch!

[Sharps40]

If you can find a Rochester B that don't leak as much gas as flows thru it! HA!!!!!!

[Sharps40]

Most recent trip to the Low Country netted an average mileage of 18.7ish at various speeds 60 to 70 mph....mostly around 60. Some city drivin in there. Trip back was durn close to 20 at about 19.6 mph, we had no city drivin on that pass.

[tincan1966]

Originally Posted by Sharps40

If you can find a Rochester B that don't leak as much gas as flows thru it! HA!!!!!!

I've never had a problem with one. Got a pretty consistent 16-18 mpg with my '66 GMC 250/4 spd and 3.23 gears.

But I am all about EFI now- so much easier and no adjustments required.

[NEWFISHER]

I have a worked over 250 in my daily. Lump ports, hei, z28, big cam , milled , balenced, cast headers, clifford and 390. I get 16 to 19.5 with a 700r4. And 3:73. It was worse with the 4spd and 3:08s. Tons of torque, good power great milage. Look up Tom at 12bolt.com and follow his direction. Problem is, you can build 3 or 4 small blocks for what you will have in the warmed up 6.
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[Sharps40]

Originally Posted by NEWFISHER

I have a worked over 250 in my daily. Lump ports, hei, z28, big cam , milled , balenced, cast headers, clifford and 390. I get 16 to 19.5 with a 700r4. And 3:73. It was worse with the 4spd and 3:08s. Tons of torque, good power great milage. Look up Tom at 12bolt.com and follow his direction. Problem is, you can build 3 or 4 small blocks for what you will have in the warmed up 6.
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Not really the price of 3 or 4 but maybe one moderate 8. Anyway, the six always torques better/lower than the 8. And, a six is never JAFSB !!!!

I could see mileage being worse with a 6 and the 308 rear. Trucks are heavy and bricklike and the motor is small. Pretty much seems you may have it lugging all the time with 308s.

[TJ's Chevy]

I have a 600 cfm edelbrock 4 barrel and headers and hei on my 292. Stock 4 speed and I believe 3.90 gear ratio with 30/9.50/15's for tires. At 2500 rpm I'm doing about 50-55(my speedo is junk) and I'm probably getting around 16. At that rpm I'm just touching the pedal and when I jam into it fuel milage goes to 4 mpg!!! Well.....Maybe not that bad....