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gas mileage

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by chevidog, Jun 14, 2000.

  1. chevidog

    chevidog Registered Member

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    Wow! Just averaged 10 mpg on highway over 100 stretch at 65 mph in my 78 Jimmy. This can't be typical. I have a stock drivetrain with a stock 400 with a holley carb. I can't tell what kind of carb it is, looks new and does not have fuel bowls and is not efi (I wish). I love driving the Jimmy with the top down, but had to quit driving it because of the fuel consuption problem. I plan on installing a 383 from my chevelle soon, I averaged about 15 mpg in town in the chevelle. I don't want to waste my time with the swap if I can't get better fuel mileage than my approx. 7 mpg in town now,since I won't be able to afford the gas. My question is what is your typical fuel consumption in town or on the highway?
     
  2. Kelboski

    Kelboski 1/2 ton status

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    i have a 305, W/edelbrock 4 barrel q-jet, and i get around 11city/19-20highway miles per gallon
     
  3. Donovan

    Donovan 1/2 ton status

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    I am getting around 15mpg in town with my 73 blazer. It has a caddy 500 with 3.08 and 31inch tires.

    Donovan
     
  4. DMK

    DMK 1/2 ton status

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    Had an 78 k-10 stepside with 34,000 original mi. 350 th350when it was full time 4x4 got about 10 mi to gallon on expressway and 8-9 city. After conversion it was about 11/15. Everything was stock. Did have fresh tune-up.
     
  5. HarryH3

    HarryH3 1 ton status Author

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    383 TPI in a '75 K5 - I don't even check in town, I don't want to know... [​IMG] About 13.5 on the highway. 4.10s and 35's with 3/4-ton axles.

    Stock 350 in a '94 Suburban - 10-11 in town, 13-14 on the highway. 3.73's and 265-85/16's.

    Modified 4.3L in the S-Jimmy - 14 in town, 15-17 on the highway.

    K5's typically don't get the greatest mileage. Big tires have a negative effect. Speaking of big tires, be sure that you include your speedometer/odometer error in your mileage calculations. If you've swapped to 35's but didn't change axle gears or the speedo drive gear, then you're really traveling a lot further that your odo indicates. (You're also moving a lot faster than it indicates!) [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    http://ThunderTruck.ColoradoK5.com
     
  6. chevidog

    chevidog Registered Member

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    Thanks for the info. I still have full time 4wd, might have to convert to part time. I have heard negative effects of this conversion but it might still be cheaper for me in the long run (as long as gas prices are this high). Still have original diameter tires, but not for long.
     
  7. Boss

    Boss 1/2 ton status Author

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    7mpg, on new 350 crate, quad carb, 7"s of lift, 35" tires, and a heavy ass ride.
    Boss
     
  8. Jeff427

    Jeff427 1/2 ton status

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    Donovan, was it very difficult to install the 500 Caddy in your 73? I have a 78 that I'm putting a 472 Caddy in and was wondering what to watch out for.

    Jeff427
    <font color=red>Mud Dog Off Road Club</font color=red>
    http://jeff427.coloradok5.com
     
  9. Burt4x4

    Burt4x4 3/4 ton status

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    350,Edelbrock 750 Q-jet, SM465, 3.73 33"Mudders get about 8-10 in town(if I can keep my foot out of it)10-13 Hwy road trip cruzing and not opening the secondarys.....

    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
    http://burt4x4.coloradok5.com
     
  10. Balou

    Balou 1/2 ton status

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    back to Germany
    '79, 350 edelbrock performer and 600 carb., 3.40 gears, 35"
    13mpg highway and town

    hhhhmmmm, what will happen to the 400 ???

    Balou
    '79 K5,350,465,205
    [​IMG]"Size DOES matter!!!" said the girl last night [​IMG]
     
  11. Donovan

    Donovan 1/2 ton status

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    This is the best swap that I could have did. I had 350,396,427 and a 454 in this blazer and the stock caddy runs better than any of them. The valve cover will be close to the brake booster but the cover will still come off. I did not move the engine forward like most do because I would have to get new drivelines and I didn't want to mess with that. So what happens is that on the firewall there is a lip that comes out about 2" and this is about the area that the top two tranny bolts go into the block. I took the plasma cutter and cut this lip off but about 1/4" left. I pinned the two lips together and welded the lip up and it looks close to factory but not quit. This gets rid of the problem with putting caddy's in to trucks or blazers. I think that I have some pictures of it I believe. Next was the motor mounts and all I did is move the mounts forward to the 6 cylinder mounting on the left side and then match that on the right side. I just sloted the factory bracket for the caddy mounts. The engine will sit in there just right. I used the eldo top radiator hose and the bottom hose is a stock small block hose and that is it. If you need more info let me know and I will try to get some pictures of it for you.

    Donovan
     
  12. Bigd

    Bigd 1/2 ton status

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    Donovan, while on the subject of 500 caddy moters.I was wondering about bell housing bolt patterns are they the same as chevys.I have a manual tranny,what about flywheels?I would be very interested in this kind of swap.Any help would help thanks.
     
  13. Kyle89K5

    Kyle89K5 1/2 ton status

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    I'm pulling down just a tad over 16 in my 89 now. Rebuilt the TBI and did a MAJOR tuneup that involved changing ALL the sensors. I also don't do over 65 mph. If I take mine up to 75 my miliage drops quit a bit. Intown driving doesn't seem to bother it all that much, I'm just easy on it, and idle through most of town

    I'm still running the 31's with a 350, 700R4 tranny and 241 case, ALL with 190,000 miles on em. As for gear ratio's, I haven't the foggiest, all I do know is that at 85, it's beggin for me to slow down. Not much in the way of performace mods either, 3" single flowmaster exhaust, and a K&N. The thing ran to good from the factory for me to mess with it.

    Kyle
    89K5
     
  14. Donovan

    Donovan 1/2 ton status

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    Yes the bell housings are different. The use the BOP case. I have been told to find a bell housing for a pontiac and they work the best. Also MTS sells flywheels for the manual trans. You will need to drill the crank for a pilot bushing. I will try to get some pictures.

    Donovan
     
  15. 90K5

    90K5 1/2 ton status

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    I get 10mpg if im lucky in the city and the guy i bought it from said he got 14 on the highway but i never drive on the highway and i have a heavy foot so i dont know if thats true.
     
  16. Laurie

    Laurie Registered Member

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    Same here w/ my 87. 10 mpg city, hwy ??? can't wait to hit the road and find out.
     
  17. Zack

    Zack 1/2 ton status

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    Well not to show anyone up or anything but I get 25.7 on average city/hwy combined. This is with stock tires and stock gear ratios.. Around 35 is what i get with just hwy driving. Oh I can do 105 mph when the fuel system shuts off cause the computer doesn't want me to go any higher (awww) and at 105 I am only pulling around 4 grand on the tach.. Well sorry if I am making anyone mad here..



    ....



    ....


    ....

    Did I mention that this is with my 97 Grand Am Gt? LOL Well with the blazer I get around 7-8 so that's why I bought the grand am.. And the chicks dig it alot more.

    <font color=red>Zack Carlson</font color=red>
    <font color=yellow>Carlson@thestix.net</font color=yellow>
     
  18. HarryH3

    HarryH3 1 ton status Author

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    Zack, you're too funny. [​IMG]

    Several years ago I bought a brand new Chevy Beretta GT. Before it was 2 weeks old I was airing it out on a country road. When the computer shut down the injectors I thought that I had blown the engine. I was looking in the rear view mirror for smoke and parts tumbling along behind me. At about 103 the injectors came back on. Freaked me out!

    I later found out that the lawyers make 'em do that. The tires that come on the GT are only speed rated to 108 mph. Can't have anybody buzzing along at a buck-twenty or better and have their tires self-destruct! [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    http://ThunderTruck.ColoradoK5.com
     

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