Gas mileage increase- six to BB OD - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ZEKE68 · 11-29-2018, 08:38 PM

Just wanted to post this for who ever is interested, but I replaced my 250 six Powerglide trans with a .030" over 454 and a overdrive automatic and got over two miles per gallon better mileage. Always got around 9.8 to 10 with the old power train. Just got 12.3 mpg the last tank with the big block overdrive.

**70STOVEBOLT** · 11-29-2018, 08:45 PM

What trans? I made the switch from 250 to 402 but I kept the TH400 and I have not had a chance to check the MPG because the TH400 gave up the ghost.

notsolo · 11-29-2018, 08:47 PM

Good that the milage is better, still seems low to me. 6 with powerglide I would have guessed 15-18 mpg....What gears are in the rear?

**70STOVEBOLT** · 11-29-2018, 08:52 PM

The best I got with mine with the six was 14 with the stock 3.73 gears.

ZEKE68 · 11-29-2018, 10:36 PM

Running 3.73 gears. Tires are 31.3 inches tall. Running 2474 rpm at 80 mph. The new transmission is a 4L80E with 2200 to 2400 stall factory converter. Running two Edelbrock 500 cfm AVS carbs on the 454.

weim55 · 11-30-2018, 02:07 AM

Certainly the real smile on your face comes from the most important gain of the swap:

HORSEPOWER!

Could there be a worse slug than a 250 'glide in one of these heavy barn shape trucks (??!!) Maybe a diesel Chevette......

Steve weim55 Colorado

Katrina/10 · 11-30-2018, 09:29 AM

Quote:

Originally Posted by weim55

Certainly the real smile on your face comes from the most important gain of the swap:

HORSEPOWER!

Could there be a worse slug than a 250 'glide in one of these heavy barn shape trucks (??!!) Maybe a diesel Chevette......

Steve weim55 Colorado

I drove a diesel Chevette. It was slow!

67ChevyRedneck · 11-30-2018, 10:30 AM

I ran my 250 six for a few years with the stock 3 spd and 3.73 rear and the best I ever got was 11-12. Really liked that motor though. Always lit right off and idled like butter. Kinda mad at myself for yanking it out for a 350 many years ago. Looking back I wish I had just added a T5 behind it.

11-29-2018, 08:38 PM	#1
ZEKE68 Registered User Join Date: Jul 2012 Location: Space Coast, Florida Posts: 403	Gas mileage increase- six to BB OD Just wanted to post this for who ever is interested, but I replaced my 250 six Powerglide trans with a .030" over 454 and a overdrive automatic and got over two miles per gallon better mileage. Always got around 9.8 to 10 with the old power train. Just got 12.3 mpg the last tank with the big block overdrive. __________________ 1968 SWB Step Side, Big Block, 4L80E , Running!

11-29-2018, 08:45 PM	#2
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,212	Re: Gas mileage increase- six to BB OD What trans? I made the switch from 250 to 402 but I kept the TH400 and I have not had a chance to check the MPG because the TH400 gave up the ghost. __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Power windows Power Locks Coming soon: EFI 2015 Silverado 1500 LS 4.3/6L80/3.23

11-29-2018, 08:47 PM	#3
notsolo Registered User Join Date: Apr 2008 Location: Md Posts: 2,451	Re: Gas mileage increase- six to BB OD Good that the milage is better, still seems low to me. 6 with powerglide I would have guessed 15-18 mpg....What gears are in the rear? __________________ http://67-72chevytrucks.com/vboard/s...d.php?t=635605

11-29-2018, 08:52 PM	#4
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,212	Re: Gas mileage increase- six to BB OD The best I got with mine with the six was 14 with the stock 3.73 gears. __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Power windows Power Locks Coming soon: EFI 2015 Silverado 1500 LS 4.3/6L80/3.23

11-29-2018, 10:36 PM	#5
ZEKE68 Registered User Join Date: Jul 2012 Location: Space Coast, Florida Posts: 403	Re: Gas mileage increase- six to BB OD Running 3.73 gears. Tires are 31.3 inches tall. Running 2474 rpm at 80 mph. The new transmission is a 4L80E with 2200 to 2400 stall factory converter. Running two Edelbrock 500 cfm AVS carbs on the 454. __________________ 1968 SWB Step Side, Big Block, 4L80E , Running!

11-30-2018, 02:07 AM	#6
weim55 Registered User Join Date: Jan 2017 Location: Larkspur, Colorado Posts: 904	Re: Gas mileage increase- six to BB OD Certainly the real smile on your face comes from the most important gain of the swap: HORSEPOWER! Could there be a worse slug than a 250 'glide in one of these heavy barn shape trucks (??!!) Maybe a diesel Chevette...... Steve weim55 Colorado

11-30-2018, 10:30 AM	#8
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	Re: Gas mileage increase- six to BB OD I ran my 250 six for a few years with the stock 3 spd and 3.73 rear and the best I ever got was 11-12. Really liked that motor though. Always lit right off and idled like butter. Kinda mad at myself for yanking it out for a 350 many years ago. Looking back I wish I had just added a T5 behind it. __________________ Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride American Born, Country by the Grace of God 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications!



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