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85 k-10 question

Discussion in 'Chevy Trucks' started by Chevytruck85, Jan 11, 2008.

  1. Chevytruck85

    Chevytruck85 Senior Member
    Messages: 228

    I have a 1985 k-10 that i recently re did and put a 350 crate motor in with a edelbrock performer intake and a 670 cfm holly carb. I always new it got bad gas millage but i decided to check it anyway and its getting 6.5 around town and 9 on the highway i was expecting at least double digits. I dont know if a smaller cfm carb would help or maybe i need to go back to the stock quadrajet let me know if anyone as an idea THANKS
     
  2. Milwaukee

    Milwaukee 2000 Club Member
    Messages: 2,180

    What barrel you have? My teacher from auto shop say 4 barrel on 350 get around 8 mpg but with 2 barrel it get around 13 to 16 mpg.


    I would put original carb on that to see if it improve mpg.
     
  3. Chevytruck85

    Chevytruck85 Senior Member
    Messages: 228

    its a 4 barrel and the stock one is also a 4 barrel
     
  4. tom_mccauley

    tom_mccauley Senior Member
    Messages: 465

    carb size has less to do with mileage, than the size of the cam. Is it an aftermarket cam or OEM?
     
  5. Sydenstricker Landscaping

    Sydenstricker Landscaping PlowSite Veteran
    Messages: 3,882

    670 cfm doesnt seem that big. Is there anything else done to the engine??? Could be your secondaries are kicking in too early??? Just for the heck of it, toss the stock quadrajet on and see what goes. That sounds really low mpg though. Both of my 82/84 K20's with the 350's got around 10 or so city and maybe 16 freeway
     
  6. Chevytruck85

    Chevytruck85 Senior Member
    Messages: 228

  7. Chevytruck85

    Chevytruck85 Senior Member
    Messages: 228

    the engine package comes with a 600 cfm edelbrock i dont how much of a difference that would be from my 670 holly??
     
  8. tom_mccauley

    tom_mccauley Senior Member
    Messages: 465

    the cam you have is NOT a stock profile (.383''/.401'' and 112° lobe separation) this cam is closer to the "R.V." cam it is designed for low end torque(350 ft-lbs). the stock sbc cam has a profile of (252/261 with a 109 degree centerline.) Taken from desktop Dyno. This would explain why you mileage has dropped into the single digits. My 72' Skylark w/ SBC 355 gets about 4-5 mpg how s***y is that!!

    P.S. Jegs engine's are flippin bulletproof! My buddy spun his up to 7500 RPM's and the damn thing held together Bone stock!!!!!!!!
     
    Last edited: Jan 11, 2008
  9. tom_mccauley

    tom_mccauley Senior Member
    Messages: 465

    The edelbrock is a better all-around carb, than the holly. I run twin 4150's on my buick

    [​IMG]

    [​IMG]
     
    Last edited: Jan 11, 2008
  10. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    if you want the best of all around performance and power and fuel milage. you need to swap in t.b.i . get a good used system or a kit for a 350 and be 5-6xhappyer than carb.

    i swaped a newer cab on my 79k30 and kept the t.b.i. and wow what a diffrence. i can use a remote start if i want. runs better. better tourqe and better fuel milage.

    you just need to watch the cam specs to be safe with tbi needs.
     
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The cam in your engine definitely isn't what I'd call too large by any means... since basically what you have is a stock service replacement engine... nothing out of the ordinary about the engine itself as far as making it hard on gas. I've used cams more sizable than the relatively stock cam in your motor with excellent results..

    The biggest issue that's going to affect you MPG is th gear ratio/ tire size on your Blazer and the carb. Do you know what gears are in it? What size tires? Since you said that your running a 670 cfm Holley, it must either be a Truck or street avenger series, neither of which is noted for their efficiency or fuel mileage. If you'd reinstall the Q-jet you'd instantly gain MPG's as it's one of the most efficient carbs GM ever had plain and simple.. Ignition timing can also greatly affect you MPG, what do you have the timing set at?..
     
  12. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    As B&B said, the quadrajet is an awesome carb, but they did get a bad rep for not being easy to work on and working poorly when they ge old and dirty. But you can't beat a nice fresh one. In fact Edelbrock sells them now, little pricy.
    Personally I've never had anything but bad luck with Holleys, can't go a full day without opening the hood and tweaking it. I have owned a bunch of Edelbrock 600s, I absolutely love them. Bolt it down, shut the hood and forget about it. In fact every time I buy a carbed vehicle the first thing I do is throw a new 600 on it.
    Milwaukee, I think your auto shop teacher needs to go back to school. 2 barrels are notorious for being worse on fuel than a 4 barrel with vacuum secondaries. And you cannot put blanket fuel mileage on a motor, it depends on the vehicle
     
  13. tom_mccauley

    tom_mccauley Senior Member
    Messages: 465


    Well Said!!
     
  14. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    Who said anything about a Blazer? I read K-10.
    Those years a lot of half tons (and Blazers) came through with 3:08 gears. Decent highway gear especially with an overdrive, but not great for pushing snow or towing anything. And if you start upsizing tires it doesn't take long to get the motor out of it's happy range and into lugging and wasting gas range. Not to mention larger tires will blow the axle-fuse.
     
  15. Chevytruck85

    Chevytruck85 Senior Member
    Messages: 228

    It has 3:08 gears 31 inch tires and the overdrive transmission, nothing to out of the ordinary.
     
  16. Chevytruck85

    Chevytruck85 Senior Member
    Messages: 228

    I was also looking at the edelbrock performer 600 card on jegs one of the carbs says its tuned for maximum performance and the other choice says its tuned for maximum fuel economy what is the difference between these carbs is the jets or something??
     
  17. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Sorry Dan, "Blazer" was a typo on my part..:cry:

    The difference between the Edelbrock 1405 (max performance) and 1406 (max econ) series is just a minor change to the primary and secondary jetting and power enrichment springs. And the 1405 is a manual choke, 1406 is an electric choke. Other than that, they're the same carb.... and neither will match the fuel economy or efficiency of a tuned Q-jet... nothing wrong with them as I have used plenty of E-brocks carbs on performance applications, but for MPG's it's hard to beat a good Q-Jet...

    Since your truck has 3.08's and only 31's I wouldn't consider that as being your fuel mileage killer, maybe not ideal for a work/plow truck with a 700R4, but shouldn't affect the MPG greatly over a bone stock set up.

    Do you know what you have the timing set at?

    Are you still using the original HEI distributor that has the extra 4 wire connector for the computer controlled timing? If so and the rest of the under hood sensors have been disconnected, it isn't supplying any ignition advance as the RPM increase, and will kill the gas mileage (and power) in a heart beat.

    An '85 should've originally had both the computer controlled HEI , and a feedback style Q-Jet. Does it?
     
  18. extra mile

    extra mile Junior Member
    Messages: 9

    how many miles have you put on the engine? The mileage can be abnormally low on a fresh engine until everything wears in a little. Are you sure the Torque convertor is locking up in a least overdrive? This can make a huge difference in the mileage you will get.
     
  19. WheelerandSon

    WheelerandSon Member
    Messages: 74

    Try running the 600 Edlebrock Carb. I did the same with my 70 Nova that I just put a new 350 in and I get decent fuel mileage. Of course, it is a much lighter car. What tranny are you running? THat also has alot to do with your fuel mileage. I know alot of guys swith from the 350 turbos and 400 turbos to the 700R4 so they have overdrive. that too will improve your gas mileage.
     
  20. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Four barrels get better mileage than two barrels because of the smaller throttle blades, meaning they pass less air/fuel when its not needed.

    Keep in mind also as tire sizes increase (stock would have been LT235's I think, around 28.5" tall vs your 31's) you are actually travelling farther per revolution of the wheel, making your mileage maybe seem lower than it is.

    The circumference of a 235 would be approximately 89.54", a 31 would be approx. 97.39". These numbers are also the distance travelled per revolution at the wheel. Thats about an 8% difference because of the tire size... or in other words you are travelling 8% farther on a gallon of gas than your speedo says you are.

    So, if your speedo says you are getting 9mpg on the highway, in reality you are getting almost 10.

    Also a 31"er is heavier and usually has a bigger footprint, (even worse with more aggressive tread types) it may be costing you one or two miles per gallon versus the stock tires.

    You're probably not that crazy far off from what it should be. Thats not to say theres no room for improvement...