Why do I burn so much fuel??? - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Longhorn Man · 03-01-2007, 11:30 AM

brak... it all depends on the truck. Some trucks will get better MPG with the tailgate up, and some with it down. It depends on the length of the bed, the shape of the cab, the size of the truck... etc.
Nascar guys spend millions on the aerodynamics of there cars... and that truck seris, they have 3/4 length hard covers. They may know something you don't.

With that being said... on our old trucks, which have the aerodynamics of a barn door, there is no gain from dropping the tailgate.

chopper103in · 03-01-2007, 01:06 PM

with the 373 gear i had i got 10 mpg no mater how i drove it
have a 307 gear now and it does a lot better ----some where around 16

Longhorn Man · 03-01-2007, 01:19 PM

once you install the 700R4 with that gear out back, you'll be back down to 10, if not less.

**WorkinLonghorn** · 03-01-2007, 03:52 PM

Actually,when I had my old pre-"rebuilt" engine I regularly got 12 MPG no matter HOW I drove or what loads I carried occasionally. I had the timing dialed in with an adjustable Vac. Adv. There is a little cam that comes with this kit that controls when the advance starts.I lost that and I've never gotten 12 since.Only 10 now.

brak · 03-01-2007, 04:09 PM

i regularly got 12+ in my 81 c-10. of course that was a goodwrench 305, with an edelbrock performer intake, and edelbrock 1406 carb, dialed in exact.

350's and up tend to drink a little more

sb69chevy · 03-01-2007, 04:53 PM

I got about 13 or so last week.

chevguy7 · 03-01-2007, 05:05 PM

I just don't check mine.

bcanini · 03-01-2007, 05:37 PM

Quote:

Originally Posted by chevguy7

I just don't check mine.

I agree!!!!

**70STOVEBOLT** · 03-01-2007, 05:38 PM

The best I've gotten is 15.2, but that was before I ditched the saginaw for the TH400. With 3.73 gears it tachs around 2500-2600 at 55 mph. I think 3.42 gears would improve it, but I need all the power I can get with the little 250!!

TP from Cntl PA · 03-01-2007, 06:43 PM

Personally, I think the tail gate up increasing mpg's is B.S...............Because every truck we've installed a stake body on the mpg's increased(Just running a flat bed, no sides). Also, the stakes are way heavier than the stock bed.............In the end it doesn't add up that putting the tail gate up would increase mileage, or our farm trucks would take a HUGE hit when we remove the stock box to swap it for a stake.

**WorkinLonghorn** · 03-01-2007, 09:37 PM

Quote:

Personally, I think the tail gate up increasing mpg's is B.S...............

I used to put mine down until I saw a study by some automotive engineers (iirc) who studied the air flow pattern with it up and down and the drag was actually SLIGHTLY less with it up.The theory was that the path of the air sweeping past the cab was infinitesimally better,and the pressure at the back of the cab was ever so much higher with the tailgate UP.
>>But either way isn't going to make much if any difference in MPG.
>>Also I remember them explaining that it isn't like the air hits the tailgate and stops.There is a cushion of air maintained at the tailgate and oncoming air sails past with negligible drag.

03-01-2007, 11:30 AM	#26
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Why do I burn so much fuel??? brak... it all depends on the truck. Some trucks will get better MPG with the tailgate up, and some with it down. It depends on the length of the bed, the shape of the cab, the size of the truck... etc. Nascar guys spend millions on the aerodynamics of there cars... and that truck seris, they have 3/4 length hard covers. They may know something you don't. With that being said... on our old trucks, which have the aerodynamics of a barn door, there is no gain from dropping the tailgate.

03-01-2007, 01:06 PM	#27
chopper103in Registered User Join Date: Dec 2006 Location: sycamore,il Posts: 163	Re: Why do I burn so much fuel??? with the 373 gear i had i got 10 mpg no mater how i drove it have a 307 gear now and it does a lot better ----some where around 16 __________________ 69 chevy swb 2.5 in droped spindle with 1 coil cut--5 in dropped spring in rear 5 in dropped spring 307 repaced soon with 350 3sp on tree soon replaced with 350 tubo 06 monte carlo 94 chrysler town & country---198K 84 jag xj6 76 sportster---57 panhead

03-01-2007, 01:19 PM	#28
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Why do I burn so much fuel??? once you install the 700R4 with that gear out back, you'll be back down to 10, if not less.

03-01-2007, 03:52 PM	#29
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,883	Re: Why do I burn so much fuel??? Actually,when I had my old pre-"rebuilt" engine I regularly got 12 MPG no matter HOW I drove or what loads I carried occasionally. I had the timing dialed in with an adjustable Vac. Adv. There is a little cam that comes with this kit that controls when the advance starts.I lost that and I've never gotten 12 since.Only 10 now. __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

03-01-2007, 04:09 PM	#30
brak Registered User Join Date: Apr 2006 Location: MinneSNOWta Posts: 1,381	Re: Why do I burn so much fuel??? i regularly got 12+ in my 81 c-10. of course that was a goodwrench 305, with an edelbrock performer intake, and edelbrock 1406 carb, dialed in exact. 350's and up tend to drink a little more __________________ 2003 GMC Sierra 1500 WT 1995 Nissan Hardbody 2016 Hyundai Veloster Turbo DC2 (SW/AW) Clyde W. Harvey USN "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery" Winston Churchill

03-01-2007, 04:53 PM	#31
sb69chevy Registered User Join Date: Oct 2006 Location: Springfield, MO Posts: 375	Re: Why do I burn so much fuel??? I got about 13 or so last week. __________________ 1969 C/10 swb, 350, powerglide (daily driver) 2005 CRV (wife's ride)

03-01-2007, 05:05 PM	#32
chevguy7 Registered User Join Date: Oct 2006 Location: Washington Posts: 316	Re: Why do I burn so much fuel??? I just don't check mine.

03-01-2007, 05:38 PM	#34
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,359	Re: Why do I burn so much fuel??? The best I've gotten is 15.2, but that was before I ditched the saginaw for the TH400. With 3.73 gears it tachs around 2500-2600 at 55 mph. I think 3.42 gears would improve it, but I need all the power I can get with the little 250!! __________________ 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 Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear

03-01-2007, 06:43 PM	#35
TP from Cntl PA Registered User Join Date: Apr 2003 Location: Central PA....In the Berg of Nisbet Posts: 790	Re: Why do I burn so much fuel??? Personally, I think the tail gate up increasing mpg's is B.S...............Because every truck we've installed a stake body on the mpg's increased(Just running a flat bed, no sides). Also, the stakes are way heavier than the stock bed.............In the end it doesn't add up that putting the tail gate up would increase mileage, or our farm trucks would take a HUGE hit when we remove the stock box to swap it for a stake. __________________ '72 K-20 EFI'ed 250 Inline/4spd stake body, Farm Truck '71 C-20 Cummins Diesel Powered, In storage thanks to $5.00 diesel! '69 3500 GMC 305V-6/4spd, Still under reconstruction.......... Inlines Rule! 6 soldiers standing is better than 8 laying down!!!!!!!!



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