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Looking for a Cummins 3.9BT specific forum, Help!

Discussion in '1982-Present GM Diesel' started by grimjaw, Jan 27, 2006.

  1. grimjaw

    grimjaw 1/2 ton status

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    I am looking for a Cummins 3.9BT specific forum. ANyone know of a good one? I am getting comparison info together for different diesel options. Thanks.
     
  2. imiceman44

    imiceman44 1 ton status

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    Whar are you doing the research for?
    I haven't found a 3.9 specific forum but I know of a couple of guys that have it in their K5 and they say it works great.
     
  3. grimjaw

    grimjaw 1/2 ton status

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    I am comparing the cost, reliability, possible power, fuel economy and ease of swap between the GM 6.2 -6.5 and Cummins 3.9BTs.
     
  4. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    look for the 4bt group on yahoo, there are a few of us on there
     
  5. grimjaw

    grimjaw 1/2 ton status

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    I have that group. I am just looking to see if there is any more places to get info.

    Thanks.

    It would help if there was a program like Desktop Dyno for Diesels.
     
  6. CrewCab59

    CrewCab59 1/2 ton status

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    Cummins 3.9

    What info do you need ,I can help with the parts I have a complete P 30 .
    ask away.

    3.9 can get up to 25 mpg with good power,say 300HP

    A 6.2 or 6.5 can't come close and won't last as long .

    (My bother is doing a 3.9 in his 84 Blazer,he just getting parts together ).

    P.S my shop is moving to knoxville, TN

    CrewCab59
     
  7. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    crawlink5 on this site just finished his conversion in a 79 blazer, we got it on the road yesterday.

    I'm going to be dry fitting mine with the body on soon as well in my 86
    [​IMG]

    here is a dyno curve on the 4bt.
    [​IMG]


    Ease of swap obviously goes to the 6.2 or 6.5 as they are straight bolt ins.....

    here is a pretty good 6.2 build
    http://community.webshots.com/album/286393940AoOzqp
     
    Last edited: Jan 29, 2006
  8. crawlink5

    crawlink5 1/2 ton status

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    I certainly like the engine! If I can just get my brakes working...
     
  9. grimjaw

    grimjaw 1/2 ton status

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    To hijack my own thread....Hydroboost brakes are your friend.


    I am interested in what is needed to get 240+hp 450+tq and keep 25+mpg. Is this using comman parts or do you need that rare, only made 30 years ago, part?
     
  10. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    Yes indeed



    Basically turning up the fuel pump starts barking out the tq and HP, however that starts = fuel mileage loss, I'll have to find the spec sheets I had printed, I believe the 4bt that I saw with simillar numbers to what you posted was down in the teens on mileage. Still beating a gas motor though.

    You can also look at interchanging turbos with a 6bt for a quicker spool and more low range pep, they make higher flow injectors, pumps, etc etc......by no means is the block, internals, or compression a limiting factor.
     
  11. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    What type of injection pump is on these 3.9's? Are they rotaries like the VE 5.9's or are they inline pumps like the P7100 on the P series?

    If it's an inline bosch pump you could maybe modify the fuel plate for more fuel just like the 12v 5.9's are capable of.

    An HY35 quick spool turbo like what is on my '01 Ram auto would work perfect on the 3.9. the HY is good for basically 300HP and spools quick. The HY doesn't leave much room for fuel on the 5.9's and you could pick up an HY for cheap because of that reason, they get tossed if you want to make more than 300HP and actually tow at the same time.
     
  12. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    its a rotary pump on the 3.9's the inline ones for the 4BT are $$$$$$$$
     

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