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A few diesel questions, 4bt

Discussion in 'The Garage' started by bear76, Aug 3, 2006.

  1. bear76

    bear76 1/2 ton status

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    If I were to do the swap (4bt) into a 91' ...

    1) need a new trans?
    a) because the 91 is computer controled
    b) or because of the RPM's of a diesel
    c) or could I keep the trans (upgraded) and use a new (lowerstall)
    converter

    2) Is the current engine, 350tbi, controlled seprately from the trans?

    3) Can I still use the 241 TC, in order to keep the VSS (speedo, right?)

    4) What could I expect for a top speed with 3.73 gears and overdrive?

    5) would I have to change my gauges because I wont be using the TBI fuel tank or sending unit?

    Thank you.
     
  2. ryan22re

    ryan22re 1/2 ton status

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    Chances are that the current trans would not hold up at all to a 4bt.

    So you can just forget that.

    You would need to run a th400/4l80e or a sm 465/nv4500. Probably just switch to a manual speedo, converting your 241 to a cable drive for the speedo.

    Look in the GM diesel forum, there are several members that have swapped in 4bt/6bt's into our trucks.
     
  3. bear76

    bear76 1/2 ton status

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    these are some of the questions I could not ansewr by reading posts over there.
     
  4. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    You *might* be able to make a TH700R4 hold up to a 4BT, depending on what you do to the Cummins. It can be made to be a mean little motor, more than a built 700 could hold. It's in the lockup that I see as the main problem. The monsterous low end torque is hard on the lockup clutch and can easily break it loose without much effort on a small converter and clutch like what is found in a Th700R4 that is designed to have a much higher RPM'd lower output gas engine. I would try to get a Dodge 47RH or 518 with lockup, the Dodge Autos are much stronger with more clutch surface. Your 241 *should* still work depending on what splines are on the output shaft. If it was different you could get a Dodge 241 easily, that drops on either side.
     
  5. diesel4me

    diesel4me 1 ton status Premium Member

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    Th400..

    There are "P" series vans with Cummins 4bt motors installed by aftermarket companies--I saw a Fed-Ex truck at the boneyard last year they stripped the body right off for scrap aluminum..it had the 4bt(with turbo!),and a Chevy TH400 behind it mated with an adapter plate...bolted right in the mounts GM put there for their other engines too...

    It would have made a great donor ,had a dualie rear end and brand new leaf springs with stickers still on them too!...with the parts from a step van like that,its practically a bolt in swap..there are a few write ups on this in the diesel section here...of course no overdrive in a TH400,but at least its stout enough to handle the job it'll be doing..:crazy:
     
  6. bear76

    bear76 1/2 ton status

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    I would like to keep as much Chevy in there as possible, so maybe I should look into the TH400. Without the overdrive and low RPM's of a diesel would I even be able to get up to highway speeds? Also should I be thinking about 86ing all of the computer and electric stuff?
     
  7. ryan22re

    ryan22re 1/2 ton status

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    Um, the 91 doesn't have too much computer and electrical stuff. The ECM is about as simple as you can get as far as computers go. It only controls the lockup of the torque converter. The injection system is about the bare minimum of what you need to run the fuel and ignition.

    That stuff would have to go anyway if you swapped in the 4bt.
     
  8. crawlink5

    crawlink5 1/2 ton status

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    Yes. The 700r4 will not hold up. If you go th400 you have to get one from a 4bt as they have a pan which beefs up the housing. You cannot use a gasser th400. I am using a nv4500/np205.

    Computer will be gone

    no and no. Low end torque would kill the 700r4. Not the rpms which are from idle to 2500.

    I believe so. but you cannot use the 700r4 or the 4l60e

    I would not use an aluminum housed TC behind the 4bt. But if it doesn't work out you could always change it. NP205s are cheap.

    I ran the nv4500/205 with 3.73s and BFG AT 33s until I went 4.56. I had it up to 85 easy on the interstate. I now have 4.56 and 33s and top is 70 with OD.
    About to go to 36 hummer tires. I can go about 50 in 4th gear (1:1).

    I'm using my sending unit (1978 Blazer). You MUST change the gas tank out for a diesel tank. The galv in the gas tank will leach out into the diesel and plate out in the injection pump ruining a $600 pump. The diesel tank can be bought new surplus for $50. I took the screen off the pickup tube (or you can get a diesel screen). Remove the pump.

    My Blazer is a daily driver since early Febuary. You couldn't get me to change out the 4BT even for a 6BT.

    If you go cut corners in the drive train you will regret it. Also the frontend you use will have to be rated for the weight of the 4bt which weighs about as much as a big block - think d60.

     
  9. bear76

    bear76 1/2 ton status

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    If I'm going with the th400 from the p30 van (2wd), would the TC (lets say 205) mount right up or do I need a differnt tail shaft for a 4WD?
     
  10. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    what ever drivetrain and gear ratio you choose think of 2500 as your maxed out rpm and make decisions from there....

    As you have heard time and time again if you are thinking auto think th400 with the cummins trans brace and pan. Its not only the guts of the other transmissions that wont hold up but the housings :eek1:

    on the P30 conversions they sent out a memo that i had read one time that said not only to only use a th400 but to make sure all bracing and that special pan were in place as they were cracking housings. Dont be fooled by a 4cylinder

    You also need to check your state laws you may have to install a newer motor than your vehicle if its gonna be street and smog legal.

    The mainshaft in the 2wd 4x4 will need to be changed out to the shorter 4x4 one and then a np205 will bolt up with an adapter

    Be prepared to spend some $
     
  11. bear76

    bear76 1/2 ton status

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    I am getting the engine AND trans. out of the van (I'm getting the whole van). I will use the th400 out of the van if I can link a TC, of any make/model, to it. I understand there will be some things that need to be changed or modified to work. All bracing that comes with this trans will stay. I guess what I need to know now is what TC and/or output shafts will be needed to work?
     
  12. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Depending on the year of your 4BT, but you could use a 3GSK kit on a P pumped version. This will bring your redline to around 3,200RPM's.
     
  13. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    using the th400 with the short shaft kit any 32 spline t-case....I suggest the np205
     
  14. bear76

    bear76 1/2 ton status

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    After doing some searching, I'd like some more opinions on a divorced 205 with this 4bt/th400 project.

    Thanks.
     
  15. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    You said in a 91' I'm assuming blazer. I don't think you'll have favorable results without shifting the entire drivetrain forward as far as possible and even then your rear driveline angles would be really wild!

    A truck would be doable
     
  16. bear76

    bear76 1/2 ton status

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    If I use the th400 that's on it already, how can I beef it up? Would the torque converter be the weakest point?

    Thanks
     
  17. crawlink5

    crawlink5 1/2 ton status

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    If you use the trans currently attached to the 4bt, then you have about all your going to get as far as beef. That case is prob the strongest th400 case out there. You can call a specialty TC place and they probably can build a beefier one. Same with trans. I don't know if it is needed.

    If more beef is what you are looking for then check on Allison 1000.

    Just FYI: With the th400 you have no overdrive. I have an NV4500, 4.56 gears and 33" tires and top out at 70 mph. In 4th gear I max at 50mph.
     
  18. Drey

    Drey 3/4 ton status

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    I know Stomper has a TH350 behind his 4bt, im not sure where he got his adapter though
     
  19. bear76

    bear76 1/2 ton status

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    I just figured the trans. would need beefer internals with the added stress of a 4wd truck. If there were other ways to use another trans. with overdrive I might consider it. My current trans (gas) is a 700r4, but I am under the impression that this would not hold-up to the torque. I would think about changing gears to help with the top end speed, I currently have 10b 3.73's.

    Stomper, I you are out there and are running a Th350 behind a 4bt please chime in on your immpressions.

    Thanks.
     

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