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Would a low (380ish) horsepower 502 get decent fuel mileage?

Discussion in 'The Garage' started by afroman006, May 11, 2003.

  1. afroman006

    afroman006 1/2 ton status

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    I know that is nowhere near the full potential of an engine that big but if you had a 380 horsepower TBI 502, would it get "good" mileage (10+ MPG)? It would seem reasonable, as the engine is not being used anywhere near its full potential. Besides, 380 HP is plenty for most anything right /forums/images/graemlins/rotfl.gif? Also, are "normal" BBC parts interchangeable on a 502? For example, could you use a 454 intake on it? 454 headers? Thx for the help
     
  2. zakk

    zakk 1/2 ton status

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    10MPG in a FI 502 with the Allison is hard to get.
     
  3. Bhintz

    Bhintz 1/2 ton status

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    for gas milage it depends on how you drive, tranny (if you have o/d), rear gears, and tire size. if have small tires o/d and not to low of gears I bet you could get a tit bit over 10mpg. Almost all parts are interchangeable between BBC.
     
  4. Thunder

    Thunder 3/4 ton status

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    /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif 502 and decent fuel milage /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
    Oh man thats funny!
    I know a guy who has one in his boat. It is fed with a half inch fuel line /forums/images/graemlins/eek.gif. If that gives any indacation of fuel requirments.
    You will be lucky to get 10 driving like an old fart. Maby with FI you could get a little better.
    502 and 454 parts are the same.
     
  5. RustBuket

    RustBuket 1/2 ton status

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    maybe if you were driving on the highway downhill with the wind in neutral? /forums/images/graemlins/smirk.gif JK man I don't actually know.
     
  6. HarryH3

    HarryH3 1 ton status Author

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    Big engines require lots of fuel. Just cruising down the highway, at a given RPM, will move a BUNCH of air through the engine. The bigger the engine, the more air that will have to move through. Since the optimum air fuel ratio is around 14.7:1, then that ratio will also determine, at a minimum, how much fuel is required to keep the engine running. So a 10-liter engine would require 10 times as much fuel as a 1-liter engine at the same RPM. /forums/images/graemlins/eek.gif

    There are other factors that come into play, such as the load on the engine (ie, how hard does it have to work to maintain the correct RPM), but physics dictate that as cubic inches grow, so will fuel needs. /forums/images/graemlins/frown.gif

    It's all about this: TANSTAAFL - There Ain't No Such Thing As A Free Lunch /forums/images/graemlins/wink.gif
     
  7. bowtiepower00

    bowtiepower00 1/2 ton status

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    It would all depend on how it was built. If you kept the build mild, for example, used some merlin heads with 269cc runners, kept the compression somewhere around 9:1, and put a short duration comp 4x4 cam in it, you would have a pretty efficient engine that put out a ton of torque. With that much torque your engine would not have to work too hard to get your truck moving, and your economy wouldn't be too bad. The GMPP 502 isn't bad, but you can do a lot better if you build it yourself. With TBI i'd venture to say 10+ MPG shouldn't be too hard to achieve. I know people with stock TBI 454's that get as high as 16 on the highway. If you hammer on it, you're going to pay.
     
  8. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    I know people with stock TBI 454's that get as high as 16 on the highway.

    [/ QUOTE ]
    You can consider me as being from Missouri on that one. /forums/images/graemlins/wink.gif
     
  9. jarheadk5

    jarheadk5 1/2 ton status

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    What app is this 16mpg 502 in?? Car? Or a decent-sized K5?? Details please!

    I'm lucky to see 13mpg on the highway with my K5 (TBI 305, 700R4, 3.73, 33" BFG AT's). You show me a 502 that gets 16mpg on the highway in a K5, and I'll buy it .
     
  10. BigBurban350

    BigBurban350 1/2 ton status

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    380 hp equals 190 lbs/hr of fuel burned. /forums/images/graemlins/usaflag.gif /forums/images/graemlins/burb.gif /forums/images/graemlins/usaflag.gif
     
  11. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    [ QUOTE ]
    Would a low (380ish) horsepower 502 get decent fuel mileage?

    [/ QUOTE ] why build a 380hp 502 wen u can get that out of a small block? hell a GMPP 350ho base with 1.6 ratio roller rockers and a GMPP "hot" cam will produce 360-370. put a vortec TBI manifold on it and a good tbi and 380hp is easy. and i garantee (sp) it'll get better mileage than a 502.
     
  12. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    big burban... how did u figure that out and wat rpm is that at???
     
  13. mudgition

    mudgition 1/2 ton status

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    I agree with muddysub. If your going to buy the 502 then cut the nuts off of it, you might as well trasdplant a v-10 from the R/T dodge and pull 4 plug wires. If mileage and economy are a concern (and they always are) then build the 502 to stock specs and buy an econo-box car/truck for transportation.
    IMHO! /forums/images/graemlins/thumb.gif
     
  14. Shaggy

    Shaggy 3/4 ton status

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    [ QUOTE ]
    [ QUOTE ]
    Would a low (380ish) horsepower 502 get decent fuel mileage?

    [/ QUOTE ] why build a 380hp 502 wen u can get that out of a small block? hell a GMPP 350ho base with 1.6 ratio roller rockers and a GMPP "hot" cam will produce 360-370. put a vortec TBI manifold on it and a good tbi and 380hp is easy. and i garantee (sp) it'll get better mileage than a 502.

    [/ QUOTE ]

    <font color="green"> The difference is torque. Horspower is just a number, torque is what actually moves the vehicle. The 502 will make tons of torque down low, the 350 will not make as much torque, and what it does make will peak at much higher RPMs. In other words, the big block makes more usable power over a larger RPM range. </font>
     
  15. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    why build a 380hp 502 wen u can get that out of a small block? hell a GMPP 350ho base with 1.6 ratio roller rockers and a GMPP "hot" cam will produce 360-370. put a vortec TBI manifold on it and a good tbi and 380hp is easy.

    [/ QUOTE ]

    Torque my friend. Torque. That 502 will make more at idle than your 350 ever makes.
     
  16. afroman006

    afroman006 1/2 ton status

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    That's what I was thinking. Torque. Muddysub has a good point though. As good as a shiteload of torque sounds this burb is more of a mud truck and as such needs more top-end power. Now y'all got me thinkin. GMPP 502, GMPP 350 or 383, or a me-built 454 or stroked wersion thereof. I have a 454 2 bolt short block so I'm thinkin I may go that route but with splayed 4 bolt caps and a stroker rotating assembly. It will definately be TBI though. I just want respectable power with decent mileage (who doesnt). Oh yah this will be going into a 91 3/4 ton Sub with a 4L80E and 4.56 gears with 37ish tires. Thx
     
  17. Don

    Don 1/2 ton status

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    I run a carbureted 454 4:10 gear's, TH 350 tran's.33" MTR'S, empty or loaded, it get's around 10 1/2 on the highway in traffic considerably less. /forums/images/graemlins/eek.gif

    And as Shaggy say's, a small block will do that, and build it for torque, not h.p. /forums/images/graemlins/ignore.gif
     
  18. the cork

    the cork 1/2 ton status

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    looking at the g-m performance parts book, one of there
    338 horsepower 502s ,makes 512 ft lb of torque at 2800 rpm,
    as far as your other questions, it says not to use older mark 4 heads because of possible coolant seeping, other
    than that looks like you can use water pumps,camshafts,
    distributers,intakes, exhaust etc, some 502s require
    electric fuel pumps, as far as boats go none of them get
    good gas mileage, so dont use that as a comparison,
    i used to want a 502, now i want one again, /forums/images/graemlins/thumb.gif
     
  19. BigBurban350

    BigBurban350 1/2 ton status

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    [ QUOTE ]
    big burban... how did u figure that out and wat rpm is that at???

    [/ QUOTE ]

    Well you said 380 hp, so whatever RPM your making 380 hp. But that is peak hp, when your cruising its lower. You just take your horsepower and apporximatly %50 is your fuel usage in lbs/hr.
     

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