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268h gas milage

Discussion in 'The Garage' started by jaredmajor, Jan 30, 2006.

  1. jaredmajor

    jaredmajor Registered Member

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    who else runs a comp cams 268h cam in a 350? If so what kind of carb, gear ratio and tire size are you running. I have a holley 650cfm double pumper(horrible carb for a 4x4), 3.08(horrible gears for a 4x4), and 35" mud terrains. I have horrible gas milage, my engine makes good power though. I was thinking of switching to a 670cfm holley truck avenger. I think i would get better gas milage, and eventually 4.10's with 38.5" tsl's.
     
  2. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    i probably don't know what i'm talking about, so this is more than likely just a "bump" to the top of the list, but i think if you're trying to increase fuel mileage, you need gears in the rearend. now, i don't know ANYTHING about carbs - i'm a diesel guy, but i can guarantee you that part of your problem is your gearing w/ 35". everyone here says 4.56 is best for 35", but you can run 4.10 gears without problem. However, if you're going to be spinning 38.5's, you need something more than 4.10. if you're going to be dropping cash on your rig - i say start with the gears. if you have the stock 1/2 ton gear, it might be cheaper and easier to look for 3/4 ton gear with a gear ratio you like - that's what i did. went from a 3.42 ratio to 4.10 for under $300. i don't know for sure, but i think a single set of ring and pinion would run you more than that - plus, if you're going to 38's, you NEED more than 1/2 ton gear. ;) good luck
     
  3. theperfectgarage

    theperfectgarage 1/2 ton status

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    Colby, pretty good advice for a young dog, chem. student, drummer. It all makes sense to me.
    For the carb, yeah get the truck avenger, it's a pretty good choice. Generally speaking, thats more cam then a 4 wheeler needs but thats subjective. I would do the gearing changes first then judge the cam. Those gears your running dont give your cam much of a chance.
     
  4. sled_dog

    sled_dog 1 ton status

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    I don't think that cam is too much for a 4x4. My LT4 hot cam has more duration at .050 than that cam. But I wouldn't even consider it if you are aiming for mileage. I do not like High Energy cams. Single Pattern cams are outdated technology.

    Changing a cam for mileage isn't going to be the way to go. Colby was probably right, a better gear ratio match is going to be a better way to go for mileage. Something that lets you cruise at 65mph at about 2000RPMs and make it so your motor doesn't have to lug throught he lower gears so much. A decent tune up is a good way to get some mileage(if your carb and spark systems are tired). You noted the 2 biggest problems yourself, fix those before you go creating more problems by changing a cam and still not having gear or carb.

    In the end you are polishing a turd man. You will never get 20mpg out of your K5 with a carburated 350. If you are expecting even 15mpg I think you are aiming high. I don't know what you are expecting, but basically everyone that goes "looking for better mileage" on one of these rigs, ends up dissapointed unless they do a 6.2L swap.
     
  5. goldwing2000

    goldwing2000 Guest

    Or a 2.5L Iron Duke with 5.13 gears and a 700R4. It's a bolt-in! :haha:

    I get about 8-10 mpg on mine ('89/Carb350/TH350/3.42/35") and my buddy with stock drivetrain ('89/TBI350/700R4/33") is getting 12-13. I think mine will come up some when I swap in my 4.10s but I'm not hoping for much. I have no idea what's inside the engine but it runs good enough to give me time to rebuild my 400sb.

    That's why I bought a Mazda for a daily driver. 30mpg, baby!
     
  6. jaredmajor

    jaredmajor Registered Member

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    I would just like to get up to 10mpg. I know i will never make over 12mpg. I got to anxious when i picked my cam. I think i am going to get lower gears, probably 4.56 and then later change the cam out. It's a good cam, but not the right application.
     
  7. Muddytazz

    Muddytazz 1 ton status

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    I'm running the XE268 with the truck avenger carb and a built 350 and 4.10's with 33's and its great. Will be better once I get the carb dialed in (they are not bolt on and go like holley says, needs to be tweaked).
     
  8. jaredmajor

    jaredmajor Registered Member

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    What kind of tweaks? I think I am going to go with 4.56's, and get a truck avenger. What kind of mpg are you getting?
     
  9. sled_dog

    sled_dog 1 ton status

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    what transmission do you have? unless you have a 700R4 or 5 speed I think 4.56s would be too deep or unless you plan to change to bigger tires in the near future.
     
  10. jaredmajor

    jaredmajor Registered Member

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    I currently have a th350, but am changing to a sm465. I will eventually go to 37or 38.5 tsl's. I think the 4.56 would work.
     
  11. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    if you're going to do the manual swap, first i'll say this: congrats. :D someday i'll be there too. second, you probably don't need very low axle gears with that tranny - your 6:1 first gear will make up for alot of it. were it me and i were you and doing the swap, i'd stick with 4.10 in your case, that way you can save an extra buck cruising on the highway.
     

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