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Old 05-24-2013, 04:55 PM   #1
quik8outlaw
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gas mileage

My 88 crewcab has a 454 with a 400 trans. Like all other big blocks, it gets bad gas mileage, 6-7 mpg. would I get better mileage with a 700r4, would it be worth the hassel of changing the transmissions ? what kind of mileage could I expect with a overdrive ?
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Old 05-24-2013, 05:13 PM   #2
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Re: gas mileage

You'll get a little better with the extra gear, but I wouldn't expect much. Then again if wth gas prices these days...
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Old 05-24-2013, 07:14 PM   #3
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Re: gas mileage

x2, even at today's price of gas, it's going to take quite a while to pay for the swap.

Is 6-7 normal for you? I get 10-11 with my carburated, single cab much to the dismay of one of my co-workers with a mid to late 90's extra cab bb dually, as that is what he gets with fuel injection and OD.

Oh factor in the extra cost of getting a 700r4 built to live behind a BB, especially if you use it like a truck. I've seen 4l80e and stand alone controllers mentioned before behind 454's
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Old 05-24-2013, 08:15 PM   #4
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Re: gas mileage

You can expect 1-2 more miles per gallon. Aerodynamics also plays a big part. Lowered helps a little, a bed cover or cab high shell will also help a little. If you have 4.10 rear gears, a swap to 3.73 will also help. My lowered 92 crewcab dually with OD and fuel injected 454 got 14 mpg. it also had a cab high shell.
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Old 05-25-2013, 08:52 AM   #5
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Re: gas mileage

My 1990 454/400 Crew Cab gets 4.5-5.5 miles per gallon. I think. I don't know my odometer is accurate due to my speedo being sketchy. And I know that it's off due to my 33ish inch tall tires. Wheels and tires are ridiculously heavy, and that takes it's toll on mpg. Truck is pretty much a winter vehicle. I don't have a long drive to work (6-7 miles) so it barely gets to operating temp. **** sucks, but it is what it is and mine is waiting to get Cummins swapped...
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Old 05-25-2013, 10:38 AM   #6
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Re: gas mileage

My 75 1 ton with 454 , 4 speed with 3.73 gets around 18 mpg . The worst I have ever gotten with it was 11 mpg but I was loaded 26,000 lbs. Pulling my boats I get around 14 mpg I dont understand why you guys are getting so bad gas mileage. I am getting ready to build a 75 crew cab that I am going to put 427 and 4 speed with U S gear overdrive with 3.73 gear and I am hoping for around 20 mpg with it . I have always done great with gas mileage with big blocks .
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Old 05-25-2013, 01:52 PM   #7
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Re: gas mileage

I have a similar setup on my 82 454 th400 dually 3+3 but usually get around 11-13 Mpg mixed highway and city. As i've never done the 700r swap i couldn't help you with that question but i can tell you i never speed when the speed limit is over 55mph and i run radial tires versus the chunky truck ones. Also, if you take it easy on the acceleration your gas gauge will thank you.
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Old 05-25-2013, 02:12 PM   #8
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Re: gas mileage

Quote:
Originally Posted by RT Big Block View Post
My 75 1 ton with 454 , 4 speed with 3.73 gets around 18 mpg . The worst I have ever gotten with it was 11 mpg but I was loaded 26,000 lbs. Pulling my boats I get around 14 mpg I dont understand why you guys are getting so bad gas mileage. I am getting ready to build a 75 crew cab that I am going to put 427 and 4 speed with U S gear overdrive with 3.73 gear and I am hoping for around 20 mpg with it . I have always done great with gas mileage with big blocks .
im callin shenanigans on this one!
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Old 05-25-2013, 03:36 PM   #9
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Re: gas mileage

I too call shenanigans. My truck is a 4x4 also.
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Old 05-25-2013, 03:48 PM   #10
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Re: gas mileage

I put a Comp Cam's Extreem Energy cam in my '87 crew cab (454) , I went from 9 or 10 on the interstate to 13 or 14, my next step will be a 700R4 and 373 gears.
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Old 05-25-2013, 05:11 PM   #11
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Re: gas mileage

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im callin shenanigans on this one!
I know you dont believe me but its true ! I worked for GM for 15 years . And I do know how to get mileage out of a big bock and its real easy to do . I guess it does help I have a friend that was a engineer at GM too.
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Old 05-25-2013, 06:05 PM   #12
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Re: gas mileage

I could see it. Especially if your in a low traffic area. Sitting at a stop light for five minutes and driving for only two at a time and hardly reaching 30mph cause nobody can grab their balls and move. Well that's what destroys gas mileage
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Old 05-25-2013, 06:41 PM   #13
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Re: gas mileage

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Originally Posted by RT Big Block View Post
I know you dont believe me but its true ! I worked for GM for 15 years . And I do know how to get mileage out of a big bock and its real easy to do . I guess it does help I have a friend that was a engineer at GM too.
Well by all means share with the rest of the class! I know I for one would love to get another 10mpg out of my truck!
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Old 05-25-2013, 06:55 PM   #14
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Re: gas mileage

I'm getting 10-12 with a 1/2 ton short fleetside 3.73 rear and hard tonneau cover slammed on the ground with th400.
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Old 05-25-2013, 07:19 PM   #15
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Re: gas mileage

I got 12-14 with my crew cab dually 4x4 with the mighty 6.2 on 37's.
I got 7-9mpg with my 90 454 ss turbo 400 and 3.42 gears I had a lead foot with that truck though ha.

I would do a cummins swap and a 5 speed if you were after fuel economy.
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Old 05-26-2013, 12:32 AM   #16
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Re: gas mileage

A overdrive trans will help some but these trucks are heavy and have the aerodynamics of a brick.
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Old 05-29-2013, 12:40 AM   #17
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Re: gas mileage

I've got a dually with a 454, 4.10's and a 700r4. Don't expect big mileage gains. The big benefit is a much quieter truck on the highway; it loafs along at 70-80 now.

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Old 05-29-2013, 12:55 AM   #18
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Re: gas mileage

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I've got a dually with a 454, 4.10's and a 700r4. Don't expect big mileage gains. The big benefit is a much quieter truck on the highway; it loafs along at 70-80 now.

That is a big beautiful truck. 80 grille and 77 trim? Have you done a little customizing?
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Old 05-29-2013, 01:00 AM   #19
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Re: gas mileage

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I've got a dually with a 454, 4.10's and a 700r4. Don't expect big mileage gains. The big benefit is a much quieter truck on the highway; it loafs along at 70-80 now.

That is a really nice truck!!!!
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Old 05-29-2013, 01:06 AM   #20
jimbonice
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Re: gas mileage

I don't want to highjack the thread, but yes, it's got a1980 front end and it's a '77 from the cab back. You've got sharp eyes.
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Old 05-29-2013, 01:35 AM   #21
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Re: gas mileage

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I don't want to highjack the thread, but yes, it's got a1980 front end and it's a '77 from the cab back. You've got sharp eyes.
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Ditto, nice truck! Kind of what we have for hauling horses.
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Old 05-29-2013, 07:53 AM   #22
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Re: gas mileage

I had a 73 C20 454/400 and currently have an 83 C20 454/SM465 (both regular cab long beds) and do only city driving. I got 11 mpg best in city only driving on the 73, and get 9-10 mpg city only driving with the 83 (I attribute that to the smog equipment on the 83. The best highway mpg I got with the 83, even using the gear vendor, was 13 mpg.

If there are secrets to better gas mileage I would sure like to know what they are. I can't remove emissions equipment because I live in a emissions required part of Arizona. In city driving, I spend more time stopped and idling at intersections than driving.
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Old 12-03-2013, 08:38 PM   #23
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Re: gas mileage

I would also like to know the secrets. Too bad that dude did not follow up.

My '75 Gentleman Jim gets 9-11mpg, and that's mostly highway driving the speed limit (65 or less). 350/350

This thing needs a tune and burns a little oil. I imagine I might be able to do a tad better.
My 84' 305/700R4 got 21 @ 65mph highway until the tranny went south.
Then it never got above 17mpg. But it was a dog. I like my 75 350 better, even with the crappy mileage.

Would better heads help?
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Old 12-03-2013, 10:42 PM   #24
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Re: gas mileage

hell my 4.8 4wd 01 would only pull a best of 18 city and 22 ish highway no way i can see a big block with no od pull that. the 6.0 trucks the same year pulled a best of 16.
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Old 12-04-2013, 12:52 AM   #25
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Re: gas mileage

Just put 1538 miles on a brand new Ford F150 and my mileage was 11.3 mpg.
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