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How Many Miles to a Gallon Should A Big Ol' Road Hog Get?

Discussion in 'The Hokey Ass Message Board' started by FatChrist Magic, Dec 15, 2012.

  1. I am just not a fan of OD transmissions. I don't care if someone else runs one they are just not my piece of cake.
  2. outlaw256
    Joined: Jun 26, 2008
    Posts: 2,023


    me real reason not to like or use them. i guess im just use to 350 and 400 in my gms.and c4 c6 in my fords.
  3. Here is another real world example. My namesake for the HAMB here, a 38 Chevy 2 dr sedan, with a 468 (about 450 hp), 700R4 (with lock-up) and 3.70 geared 9-inch gets about 13 hwy if I keep it at 75 max. It has low compression and a big cam, so at 75 the engine is turning about 2500 and just smoothing out and running nice and lean if I keep my foot out of the mech secondaries. 13 is probably about as good as I can get out of it. Around town is probably about 7-8 I guess.

    The key with a big block is to use the lower rpm of an OD trans. Like a diesel engine, keep the revs lower for better mileage. Of course none of use like to drive in the slow lane, so the best way is to use an OD trans.

    An off-topic example, I have a 92 Chevy C3500 dually. 454 with Whipple supercharger, 4L80E trans and 3.73 rearend gears. It won't get better than 12 mpg hwy unloaded, at around 80 mph. Pulling an open car trailer loaded with a car and the best it gets is 9.5 hwy. It really sucks around town because the truck is so heavy, probably 6-7 range although never specifically checked that.

    I love the big block torque and figure that some mileage penalty is the price to pay.
  4. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,276


    Depends who's figures you use,my chart says 200 bucks in 1960 is 1500 today.
  5. Fat Hack
    Joined: Nov 30, 2002
    Posts: 7,709

    Fat Hack
    from Detroit

    My old 70 Chevelle with a 402 big block, 4-speed trans and 3.90 gear got an easy 20mpg on the freeway and about 14 around town with an HEI distributor and Holley 750cfm vacuum secondaries carburetor. It wasn't tuned for mileage at all, so it could have gotten better with a little effort. I'm sure 15mpg is possible with your car, unless you drive in first gear with your foot on the floor all the time!!
  6. drptop70ss
    Joined: May 31, 2010
    Posts: 1,185

    from NY

    I average 18 with the L69 305 in the buick with a qjet, 47 cadillac I am building now should average around 20mpg with the FI LT1/4l60E. I have my 396-454s sitting under the bench collecting dust. Buick will go FI when the cadillac is ready to drive.
    Last edited: Dec 17, 2012

  7. Gawd I don't even want to tell the mileage of the 283 in my current driver. I could only get 32" tires in the 16 inch old timmy mud tires and with the 4.88 (optional highway gear?) gear in that old heap it just isn't real good, of course I can pull stumps with it. :D
  8. 55driver
    Joined: Dec 7, 2008
    Posts: 130


    My 55 was recently scaled at 4000lbs + with me in it. I get 14-15 on the highway, up from the 11mpg I was getting with a th400. A 30% improvement. Overdrive is the answer!
  9. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,906

    need louvers ?

    I respect ya 'Beaner ,but I can't for the life of me figure out why folks have that attitude with them. Dollar for dollar the best car money I have ever spent. Fuel savings alone paid for the trans in the first two years with mine, it made an already silly fast car faster AND more drivable, and it's farrrrrrrrr less fragile than any four speed I have owned over the years.I'd call that win, win, win...
  10. 55chevy
    Joined: Sep 27, 2006
    Posts: 282


    I get 42 mpg on my road hog, err, Road King, love ridin that Harley as much as I can. What, a car? Never mind.
  11. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    from Noo Yawk

    I'm one that measures enjoyment in smiles per gallon, but I don't begrudge anyone for their own choices. Wanna run an auto trans? Go for it! Personally, I prefer banging manual gears. Fuel mileage be damned.
  12. drptop70ss
    Joined: May 31, 2010
    Posts: 1,185

    from NY

    Manual transmissions are great, all I run now are T56s, but I save them for the muscle cars. Muncies and T10s sit on the shelf, overdrive kicks ass.
  13. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,906

    need louvers ?

    You do realize a Tremac is a nearly indestructable 5 speed MANUAL trans, right? I personally wouldn't ever build an automatic trans car for me.
  14. 68vette
    Joined: Jul 28, 2009
    Posts: 306


    On two different occasions.......24.4 and 24.6 MPG running 70+mph on the interstate....18 around town.

    305 built by me, turbo 350 with extra clutches, 2.79 rear end.

    I took the quadrajet apart 2 times after first rebuild to get the thing zero'd in...

    Car was sold and is close to Greensboro.

    Attached Files:

  15. Mat Thrasher
    Joined: Nov 5, 2007
    Posts: 1,166

    Mat Thrasher

    I'm one of those guys but I got nothing against overdrives. I'll PM you my address so you know where to send my new Gear Vendors Overdrive! :)

    Seriously, I would love to go the GV route but at $3000 it's not in the cards at the moment. Also, I think a lot of it depends on where you live and how much and far you drive your car. In Ohio I can be pretty much any where I want to take the truck in an hour's drive. Plus running 70 around here is about as fast as you want to run anyways. Which is 3000 RPM is my truck.

    My point is it would take a really long time for me just to break even on my investment just gain a few MPG.
    Last edited: Dec 18, 2012
  16. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    Member Emeritus

    I only checked the mileage of any of my hotrods once. I was driving across the country on old rt 40 in 1968 I was driving a 63 Pontiac with a 421 SD Single AFB 4 bbl. 4spd with unknown stock rear end ratio. (it was originally a 3 spd). I was in no hurry so I drove 100 miles and put in 10 gallons. Pretty easy to calculate. I had no idea when I'd see another station.

    It had a Crower 80R roller cam shaft and kit. Not your average street cam back then. It's a good thing that I could do the math in my head or I would never know what my cars got. When we went to Memphis in 1980 the gas pump jockey said I bought the least amount of gas in our group but it was no big engine gas guzzler....283 with an adapter to the stock 36 Ford drive train. The speed limit was 55 back then right after the gas crisis.

    I'm using my original 6 cyl 3 spd OD trans behind my 352 in my 56 that I'm building.
  17. Well I think for me I have just never enjoyed the feel of an OD. The newer standard transmissions are different for sure.

    In your case it is different as well, you know how to gear a car or truck as well as how to tune one.

    One of my problems and part of the reason I never suggest one is that I see too many people just throwing an OD in a car and expecting that it makes for better mileage. The don't properly gear the car and what they end up doing is lugging their engine, which is not properly tunned to start with, around. Gas mileage does not change or it gets poorer, they just take a mediocre car and make it worse.

    I just don't see one as a catch all, and that is what they have become.
  18. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    from Noo Yawk

    Yes, I do. Those trannies are quite pricey around here. I can't justify that kind of spend, when there is no added enjoyment, and Saginaws are just about free.
  19. young'n'poor
    Joined: Jan 26, 2006
    Posts: 1,280

    from Anoka. MN

    The OP still didn't give much info. He mentioned 18 inch wheels but I'm assuming he has tires of some sort on them, what's the size? What gears are in the rear end? What cfm is the carb, what cam is in the motor, what intake what heads. You get the picture....

    Posted from the TJJ App for iPhone & iPad
  20. my old 390 ford truck could get 18MPG. 9 in town and 9 on the road
  21. That aint 18 MPG its 99, gawd everyone knows that.

    The absolute worse mileage of any vehicle I ever used was a Ford 1/2 ton with a factory 360. It belonged to a friend and I kept it tuned for him, and drove it sometimes. Best I ever got out of it was 6. He found a 428 SCJ in a junk yard that we bolted in and the mileage went up. :eek:
  22. 49ratfink
    Joined: Feb 8, 2004
    Posts: 18,132

    from California

    my 400-4-speed Pontiac 400 went from around 8MPG up to 11 when it started tossing the fan belt above 3000 RPM. the belt would fall off and the ALT light would come on. I drove around a couple weeks like that, not sure why.
  23. 4 pedals
    Joined: Oct 8, 2009
    Posts: 802

    4 pedals
    from Nor Cal

    The 360 in my wife's truck gets about 9 mpg. No matter what I do to it.

    My 427, bored and stroked to 460ci gets 13 in my El camino with a TKO600. Before I switched trannys and tuned it, got 4 mpg. swithched trannys and tune, with 292 solid roller, single plane intake, 1000 cfm carb, got 12 mpg daily.

    Detuned, 270 cam, dualplane intake, 650 carb dialed in, lotsa timing, same short block, got 13 mpg. Shoulda left it alone.

  24. I have a '93 GMC C3500 dually. With a 350 and a 5-speed manual it pulls around 13-15, the gas gauge is funky, but it turns around 2200 rpm at 65-70 in OD so it must have taller gears in it. Pulling trailer with a car on, it drops back to around 9 as well, although if I just went straight highway all the way it might do better. It's just a stock, beat up old work truck with a reman engine that has an unknown number of miles in a truck with 250,000 miles on it.

    Milage is all about torque. An engine is working it's most efficiently at the peak of the torque curve. A big engine generally puts out more torque at lower RPM so it can use less fuel to do it. But the bigger the engine in general the more fuel it's going to use.
  25. Dynaflash_8
    Joined: Sep 24, 2008
    Posts: 3,028

    from Auburn WA

    This petite little guy gets like 6-8. 454+.060 for 468. flattops and 396 oval port heads, comp 280. Roller rockers. Edelbrock dual plane 4x2 with AFBs. Dual point mallory. manifolds to glasspacks. Tranny is a saginaw 3 speed to a 3.73 rear gear.



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  26. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 9,005


    My '66 GTA Fairlane convertible with a 390 FE got 14mpg on the highway. It had 3.25:1 and C6. My '35 Chevy gets 28mpg now.
  27. bcr466
    Joined: Dec 4, 2010
    Posts: 39


    Had a 454 CC dually, 3.73, that got 11 mpg, traded for a 454 suburban same gears it got 6. Tweaked on it and driving 55-60 most it got was 13.4. My cousin had a 350/350 swb chev c10 that got 5. He installed a 350 Olds engine with 350 trans and it got 17. Over the years The Olds, Pontiacs, and Buicks I had all of them beat the chev in fuel mileage. Although the Roadmaster wagon I have now with a 350 TB will get as much as 27 highway driving it 65 mph.
  28. papawlambert
    Joined: Oct 6, 2012
    Posts: 23

    from poetry,tx

    Yeah, my 572" 56 Chev got 4 more miles to a gallon when the water pump belt came off. Drove it 3 weeks like that. [​IMG]
  29. Nailhead Brooklyn
    Joined: Jul 31, 2012
    Posts: 567

    Nailhead Brooklyn

    That's until you run out of gas... :cool:
  30. nickles street chop shop
    Joined: Jan 29, 2007
    Posts: 386

    nickles street chop shop
    from Edum Tejas

    I have a 362 SBC with a 650 edelbrock, 700R4, 3:70 gears and Eaton locker in my 62 belair wagon at 65-70mph and I get around 14. Mind you that's not straight free way. I live in the country so it's all two lane curvy ass roads. If I remember right I got 15 freeway a few years ago in Dallas with 3:36 gears, but damn those 3:70's are a lot more fun. It's a daily driver, snow or drought. So it has to be fun to drive. I'm about to put an overdrive manual in it. Interesting to see if I'll pick up a mile or two.

    and they are right, It's worth it just seeing kids jealous and old timers happy when I drive around.

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