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Why not 4bt??

Discussion in '1982-Present GM Diesel' started by Michk5, Apr 9, 2005.

  1. Michk5

    Michk5 1/2 ton status

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    Why is it that almost everyone that swap for a Cummins go for the 6bt?? Obviously you get two more cylinders, more power etc., but wouldn't it be waaaaaaaaay easier to swap the 4bt vs. the 6bt?? Maybe I'm missing the big picture :confused: ...How would a 4bt do in a K10 short box with 1 tons (4:56's),35-38's and either an auto or 465?? I really want a diesel and not to keen on the 6.2.. :1zhelp:


    I have the truck already but it doesn't have an engine...it has a rebuilt th350, but I originally wanted a SM465, and from what I have read the road manners with a manual and a detroit in the rear are less than desireable...too many decisions!! Help me do this right the first time.

    Matt
     
  2. camiswelding

    camiswelding 1/2 ton status

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    If you look at my diesel conversion post above you will actually see a 4bt going in a truck.... you might contact that member for some seat of the pants reviews

    it isnt "way" much easier.. easier yes,,, but you still are doing a conversion....and if you are doing the work why not go for the better engine.... the 4bts are down on power... but they are plentiful and cheap... they are also older less sophisticated technology ..... not necessarily a bad thing...

    the 6bt is the only way to go if you want to tow and go.....
     
  3. dallassnowman

    dallassnowman 1/2 ton status

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    Im a rookie whats a ........."4bt..or..6bt"????? :confused:
     
  4. sled_dog

    sled_dog 1 ton status

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    inline 4 cylinder and inline 6 cylinder Cummins diesel motors. The 6BT is the cummins motor that the early, mid 90s Dodges come with. Not a GM Diesel, thats probably whats confusing you.
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    The only disadvantage I can see with the 4BT is the operating range of rpms. Without an overdrive you'll be taching it out at 55 mph. At least the 6.2 will give you another 600 rpm to play with.

    6.2 makes more power stock than a 4BT anyways...although the 4BT can be bombed a lot easier.

    Rene
     
  6. Stomper

    Stomper ΜΟΛΩΝ ΛΑΒΕ GMOTM Winner

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    I can tell you your th-350 will not work in stock form. The bell housing will bolt up but the adapter ring on the flex plate has a different torque converter bolt hole pattern than the th-350's .

    Some th-400's have a converter bolt pattern of 11 1/2" dia, that is what will bolted to the 4bt.... Th-350's, along with some th-400's have a converter bolt pattern of 10 3/4".

    That being said, I don't believe that it is impossible to use a th-350, it's just going to take some modifications. I am still planning on using a th-350 with my conversion. I guess I'm a glutton for punishment :crazy:
     
  7. BlueBlazer

    BlueBlazer 1/2 ton status

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    If the 6BTs can turn 3800-4000 with a governor spring change, so can a 4BT.
     
  8. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Well, I was referring to stock...stock versus stock the 6.2 spins faster before hitting the govenor

    If we're talking about messing with govenors the 6.2 can also be governed much higher right? 4200 rpm or more IIRC.

    I know italessi has a 4BT with an NV4500 and it does amazingly well on road and off road. Without an overdrive I'm not sure the same could be said though.

    Rene
     
  9. Michk5

    Michk5 1/2 ton status

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    Great info...thanks guys!!
     
  10. mcinfantry

    mcinfantry 1/2 ton status

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    1) ive never done rocks, probably never will in my truck.

    i went 4bt for several reasons. smaller, and fits in the m715 easier. i do not run an intercooler, nor do i wish i did.

    my first gear offroad has only been used once. that was to climb a stump as a "test"

    june 2004 i wheeled in LBL, kentucky in second gear and the gassers complained incessantly about my low speed. i run 38's 4.56's and a divorced np205 giving me the rediculous crawl ratio of 50:1

    dual gear calculator

    that being said, several thoughts come to mind. gear the truck (mine for example) at 4.11's. on road my max speed with a FOUR speed would be 70mph (vs my 86 theoretical 78 actual). now 1st gear low range would be almost the same (actually a little lower)

    its the upeer 20's lower 30's fuel milage that cant be beat though. well worth the 5 speed imo.

    i find alot of diesel mis-information on the net:

    1) a cummins 4bt is too small for a 5/4 ton truck
    2) a 6.2/6.5 is junk
    3) a 6bt is really a bolt in job.

    now. had i a JUSTIFICATION of a 6bt, i may have done that. i dont tow anything 6000+ lbs so its a non issue for me. a 6bt would make the weight issue even more of a problem. for those of you curious a 6bt would put me over gvw rating for a dana 60 front axle. the 4bt has me close as it is. a blazer isnt really a good tow vehicle due to wheelbase making a 6bt even more unecessary.

    i cant pimp my movie enough, ive asked anyone anywhere to:
    1) state thier vehicle could do it as easily.
    2) explain how a 6bt could have done it better/easier

    that was an intital try at 3rd gear, the truck almost stalled, then i did it in second gear. im not a fan of snatching trucks out so id like to clarify why i did it the way i did. it was soft mud, and a nylon strap. i dont want to ride my clutch, and i tried to time it as having my foot off the clutch when the strap tightened. my foot was absolutely 100% off the clutch once the strap tightened, all i di was mash the gas.
     
  11. mcinfantry

    mcinfantry 1/2 ton status

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    id also like to add that bowtieblazer and i are currently putting a 4bt in his blazer. he has done hot springs and rode shotgun with me in LBL, kentucky. he was, and remains impressed enough to do the same swap.

    id also like to add i will either sell my 715, or steal the drivetrain and build a blazer, to fit my family.

    the th350 will not last. the th400 is not known for its longevity in the frito lay trucks.
     
  12. BlueBlazer

    BlueBlazer 1/2 ton status

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    I understand what you were getting at, but a governor spring swap is pretty cheap to have done at a pump shop (at least it should be really cheap), and AFAIK, there is not a governor spring set for a 6.2 that is easily available in the aftermarket like for the 4BT. I am not sure I would want to turn a 6.2 over 4000 anyway, despite what Mr. Heath claims to have done. The hardware limits for the 4 and 6BT is 4100 rpm, but many pullers turn it far past that. Even stock for stock, the rpm range you have with a 4BT can be utilized to work just as well as the broader band the 6.2 has IMO.
     
  13. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    That's cool Tyler. I just brought it up in case it 'was' relevant. I wouldn't be comfortable running a 6.2 over 4000 rpm either.

    Rene
     
  14. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    after I finish my conversion here in the next month or so i'll be able to tell more, my truck is around 1000lbs lighter than ltalessi's I've found more cheap easy mods to the pump, which are reversable within minutes and the overall function and simplicity of this motor is sickening.... the 1000lbs alone should really give you a kick in the pants..... 150hp 455ft-lbs of torque is easily obtainable with a stock motor, and remember TQ is all you feel until that magic # 5250?

    I can't wait to finish my rig, the mileage is my biggest pro, can't beat filling up atleast 1/3 as often as I currently do.

    I hope to be back soon with new pics and results
     

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