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Swapping a 6.2 into my '77 K20???

Discussion in 'The Garage' started by mogulmasher, Apr 13, 2007.

  1. mogulmasher

    mogulmasher Registered Member

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    Just feeling out the idea of throwing a 6.2 diesel in my '77 K20. Truck is/will be primarily used for driving to work (13 miles one way), hunting, light wheeling, dump runs, and occasional trips north hauling a enclosed sled trailer with up to 3 sleds weighing in at about 3750 lbs. or so fully loaded in very hilly terrain.

    Getting around 9 mpg's right now with a mild 350/sm465 combo with 4.10 gears and 33's. Hoping to (based on what I've read) get 15-17 with a 6.2 in this combo??? Truck is used more for driving around empty then hauling, but still needs enough power to do the work I need to when I have to.

    I found a 6.2 for $150 with 118k on it and a slight knock. Figured I wouldn't rush into putting it in, maybe throw it on the stand and spend a year or so rebuilding it.

    Can you guys talk me into or out of this???

    I know '77 never came with a diesel, but still should be a simple swap. Just need a 12 volt source, it will bolt right up to sm465, may need a diesel 4 row radiator (I have a 3 row with an electric fan now...will that work?), need to plumb in a return line to the tank, mount diesel fuel filter up on firewall, I guess you can wire glow plugs to a simple switch/button you mount to dash rather then wiring it into ignition?, and some say I need a lift pump (unclear about what this ones all about?).

    Anything else I am missing? Should work fine with my drivetrain right 465/205/44/14ff with 4.10 gears and 33" (when these are worn will swap to 35"s).

    I know the 6.2 will be down on power to my mild 350, but how bad is it? I have only driven one 6.2 in a military k5 years ago, seemed to go good, but I only drove it for a short drive. I know if I go this route it will eventually get turboed just by my nature, but might be a couple years of driving it NA.

    Sorry fo the long post....lots of thoughts rolling around in my head.....:confused:
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I swapped out a mild 355 in favor of a 6.2. Also ran the 465/205 combo behind it. I didn't feel i lost any significant power. With 4.10's and 33's you won't feel hard done by either...but you won't like listening to the 6.2 revving at 2700 rpm on the freeway either.

    My K5 has 4.56's and 39.5's, and would be turning ~2600 at 65 mph...and I averaged 16 + mpg on the highway and 15 mpg in town. I have an '83 1/2 ton with a 6.2 and 700R-4...all stock. It gets 16-17 mpg in town and 24-25 mpg on the highway.

    As for the swap you'll also need dual batteries and likely the diesel rad because the hose sizes are different on the gasser rads. The lift pump is bolted to the engine already...and if you flush the gasoline from the tanks you have you can just use them. You'll also want to swap in hydroboost brakes, instead of your vacuum booster. The diesel makes no vacuum...some have vacuum pumps but it's really only meant for tranny shifting and the vacuum AC/heater controls inside the truck.

    Glow plugs can be done manually using a big solenoid and a momentary switch in the cab.

    I'd recomend browsing the diesel forum and reading as much as possible in there for more info.

    Rene
     
  3. mogulmasher

    mogulmasher Registered Member

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    Forgot about the dual batteries. Will the second battery tray bolt on the '77 rad support?

    Also forgot about hydroboost brakes. Will a hydroboost system off any HD GM truck work with some modifications or do I need one off a 6.2? I ask cause I know lots of gasser high cube vans and the such had them and there are likely to be some in the junkyards.
     
  4. u2slow

    u2slow 1/2 ton status

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    The bigger trucks have an electric backup on the hydroboost. You might be able to make it work.
     

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