Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Is 15-16 mpg possible?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Mike's85K5, Apr 17, 2000.

  1. Mike's85K5

    Mike's85K5 Registered Member

    Joined:
    Apr 9, 2000
    Posts:
    23
    Likes Received:
    0
    Location:
    Somersworth, NH
    I'm in the process of starting my '85 K5 project truck. I'm building it to be a daily driven rig. Currently it is a 305 4-speed manual with a 2.73 gear ratio. The things I do know I'm going to do the truck is run a built 700R4 (unless you guys have a better suggestion for good mpg!) and a mild 2 1/2" lift with 33's. I also know I'm going to trash that wussey 305 (sorry 305 guys!) and run lower gears. I don't know exactly what I'm going to do for a motor yet, I've built a few smallblocks before and even have two good 4-bolt 350's to build in my garage, but I'm really thinking about buying a crate engine. I'm considering the 330HP 350HO with the vortec heads or the new HT383. What do you guys think considering it is going to be a daily driver, occasional off-roader, and full-time long distance snowmobile hauler in the winter!? Also what do you guys think about gearing? Is 15-16 mpg on the highway possible with the motors and transmission I'm considering if I ran say 3.42-3.55's with the 33-inch tires? Remember I don't four wheel really hard and I think whatever I use for a engine will have enough torque to not bog the engine with somewhat high gearing. Right? Also one more thing, the new crate 383 puts out 415 ft/lbs of torque, will a built 700R4 handle it (something like the T-700 from Jet Performance)? Any help would be appreciated as well as results with drivetrain combos you all have.

    Thanks, Mike
     
  2. Kyle89K5

    Kyle89K5 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    2,273
    Likes Received:
    0
    Location:
    OKLAHOMA
    I get about 15 mpg out of mine (again). It dropped to about 6 acouple of weeks ago. EGR valve. I've got an 89 w/ a TBI 350, 700R4, 241 case, and unclear on the gears. I've checked the miliage out over several tanks and then averaged them. It's pretty consistent, as long as I keep everything else up and running.

    The Jet 700R4 should hold up to that kind of power. It says in there ad. that it will hold u pto 450 ft/lbs. Who knows when the chips are down if it really will, but it's surely better than stock.

    Kyle
    89K5
     
  3. Blazer1970

    Blazer1970 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,600
    Likes Received:
    0
    Location:
    Old Mission, MI
    15 - 16 mpg is pretty common with TBI motors, hard to achieve with a carb. I would not run gears higher than 3.73 with 33 inch tires, especially with a 700R4. It will not help your mileage much if at all anyway.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  4. NYC K5

    NYC K5 1/2 ton status

    Joined:
    Apr 3, 2000
    Posts:
    185
    Likes Received:
    0
    Location:
    Staten Island NY/da bronx
    i would keep the 4 speed its the same trany gm put in its mediun duty trucks, it can handle insane amounts of torque. if you want good fuel economy go with a fuel injected setup a high performance ignition and low restriction exhaust. i have a carborated 350(new gm) with the 4 speed 2.73 and everything i mentioned and get an absolute max of 15 highway(usually 12-13)
     
  5. SVBlazer

    SVBlazer 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    126
    Likes Received:
    0
    Location:
    Boxford, MA
    Mike, I've got what your attempting to build...with a couple of minor differences. '85 came with a 305 (junk), 700R4, 3:73s. Replaced the 305 with a 383 and went to 33s. The tranny hasn't missed a shift or burbed at all. Had the 383 for about 5 years now. Made several other mods when I swapped the motor. I get 14+ MPG and dyno well over 400lbs of torque. Shoot me an email and I'll give you all the details on my build up.
     

Share This Page