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big block chevy in 85 k20 with manual tranny?

Discussion in 'Chevy Trucks' started by rdsealey, Jul 21, 2003.

  1. rdsealey

    rdsealey Junior Member
    Messages: 4

    I have an 85 K20 that I am in the process of rebuilding. At this time it has a GM Goodwrench 350 with a manual tranny. I think the tranny is a sm465. I am thinking about putting a big block in the truck but am riding the fence. I don't have a real reason for the BB other than I want one. I don't want to have do any fabrication to get it to fit. My problem is that I want to keep my NP208 and SM465 Transmission and just drop the BB in. Can this be done? All I can find for trannies from the factory behind a big block are TH400s. Any informtion is appreciated.

    Robert Sealey
     
  2. Pelican

    Pelican 2000 Club Member
    Messages: 2,075

    My '92 3500 has a 454 with a 5 speed behind it, don't know the tranny number, but you ought to be able to find something top work.
     
  3. wyldman

    wyldman Member
    Messages: 3,265

    NV4500's were used behind the 454's in the newer trucks.It should bolt up if you switch to a newer hydraulic clutch setup.
     
  4. rdsealey

    rdsealey Junior Member
    Messages: 4

    I know a nv4500 will bolt to a bb chevy but

    I know that an NV4500 will bolt to a chevy big block, the question is will a big block bolt to my sm465, NP208 transfer case and will I be able to keep the same driveshafts or is this going to be a really messy conversion? I would rather be able to find factory parts rather than fabricate.
     
  5. CT18fireman

    CT18fireman Banned
    Messages: 2,133

    Having done a few conversions I will tell you that driveshafts are the least of your problems if you have to move things. A shaft can be cut or lengthened for around $100. You may end up spending more time and money in engine mounts, crossmembers, and other modifications.

    Having said that I know that the BB came in the truck so it is unlikely many of these will be needed, and if you needed new shafts or anything else it probably could be found in a junkyard as these trucks did come setup with a BB from the factory.
     
  6. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    Why is he going to need to move things or get new shafts? something I'm missing :confused: (I et that way at times ;) )

    Mounts are the same for a BBC and a SBC(well the 307 and newer stuff is different but any who)

    Clutch will be the only deal if the BBC has nothing or a flexplate on it(autos have flex plates manuals have flywheels).....and honestly I havent messed with much manual stuff in these years....the older ones had linkage that mounted to the motor....but you should have hydralic so it *should* be a non issue

    456 will live fine behind a BBC, they are pretty stout.

    Bout the only thing that you need to come up with for a BBC to swap in is a different power steering pump and all the pullies and such(like fan) and then some exhaust fitment. Granted cooling might not be up to the task and fan shroud might get pissy. And deffinatly change the motor mounts when its out.....the rubber is probably 1/2 dead and the added torque might finish the job quickly

    I have a set of headers that I bought off of ebay that I never got to use when I was going to swap a BBC in my 83. They were used(not by me) but in good shape. I also have a built motor never fired 454 40 over just missing the heads. The motor probably aint an option since I'm sure the ups man would kill you on price. If interested leme know.