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Diesel torque converter on gas engine?

Discussion in '1982-Present GM Diesel' started by Steve_87K5, Feb 23, 2004.

  1. Steve_87K5

    Steve_87K5 1/2 ton status

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    I have a 6 bolt diesel torque converter on a THM400. Will this work properly behind a gas 350 engine and flex plate? Or should I get a new TC before I install the trans.? IF I use the diesel TC, can I simply use 3 of the 6 bolts or will I screw up the balance? It is going behind an internally balanced, 1977 350 gas engine.
     
  2. arveetek

    arveetek 1/2 ton status

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    The diesel TC will work, but it might lug the engine down a bit. The diesel TC has a lower stall speed than a gasser. If you're just slapping a gasser in or swapping in a diesel tranny just for a cheap repair, you probably won't notice any problems. If you're going for any performance, though, you might want to swap TC's.

    You can use just three bolts if you want to. Doesn't the flex plate have provisions for six bolts, though? I'm not sure about that. But I don't think it will matter much.

    Casey
     
  3. elacruze

    elacruze 1/2 ton status

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    I've been wondering about the difference in stall speeds. I'm getting set to install a switch-pitch TH400 behind my 6.2 with the converter from a '67 Caddy. It'll be interesting to see what rpm difference there is-those big caddy's prolly make more torque at 1500 than the diesel, so the stall shouldn't be much different. I'm researching converter experts to find someone who knows converters but diesels also-not an easy find so far. I'll add this thread to my favs and keep posted. As far as fitment, I'd be careful to check the flexplates for balancing weights, and if you find that the plate was balanced, it needs to stay with the converter or have them both balanced as an assembly, preferably with the rotating assembly of the engine. If not, then I'd try the diesel converter knowing that gas converters are a dime a dozen.
     
  4. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    I've been wondering about the difference in stall speeds. I'm getting set to install a switch-pitch TH400 behind my 6.2 with the converter from a '67 Caddy. It'll be interesting to see what rpm difference there is-those big caddy's prolly make more torque at 1500 than the diesel, so the stall shouldn't be much different. I'm researching converter experts to find someone who knows converters but diesels also-not an easy find so far. I'll add this thread to my favs and keep posted. As far as fitment, I'd be careful to check the flexplates for balancing weights, and if you find that the plate was balanced, it needs to stay with the converter or have them both balanced as an assembly, preferably with the rotating assembly of the engine. If not, then I'd try the diesel converter knowing that gas converters are a dime a dozen.

    [/ QUOTE ]

    As far as I know the diesel is internally balanced like the 350.
    The six or 3 bolts will be the same as balance goes.
    I don't think the flexplates for Gassers are drilled for 6 bolts but if they are I would use 6 bolts.
    The stall speed difference is roughly 150-200 RPM's shouldn't be a problem for a healthy engine as long as the gearing is adequate.
    /forums/images/graemlins/thumb.gif
     
  5. Steve_87K5

    Steve_87K5 1/2 ton status

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    This project is for stock performance, so I will try the 6-bolt diesel converter. B&M sells a lower stall "tow truck" converter, (maybe its a diesel spec TC!) It is supposed to also improve economy.

    I will use the gasser FP. The diesel FP does have an additional bal weight welded to it which the gasser lacks.

    I am also building a 6.5 for my 87K5, and had the rotating assy balanced crank/rods/pistons/flywheel/clutch. The tech told me that he had to use every bob weight he had to balance it.
    Can someone explain this? I assume these bob weights are temp weights he sticks on the crank somehow.
     
  6. elacruze

    elacruze 1/2 ton status

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    [ QUOTE ]
    ... The tech told me that he had to use every bob weight he had to balance it.
    Can someone explain this?

    [/ QUOTE ]

    Bob weights fasten to the rod throws and simulate the effect of the reciprocating components on the rotating balance. Obviously you can't have rods and pistons flying around the balance machine.../forums/images/graemlins/yikes.gif
    additionally, the weight of the bobs isn't 100% of the recip mass. Because the rods rotate on the bottom and reciprocate at the top, the bobs are figured as some percentage of the total rod/piston assembly mass. That percentage is calculated on intended RPM usage and vibrational/resonant issues if known.

    Eric, glad this isn't GVWR.
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    [ QUOTE ]
    Bob weights fasten to the rod throws and simulate the effect of the reciprocating components on the rotating balance. Obviously you can't have rods and pistons flying around the balance machine...
    additionally, the weight of the bobs isn't 100% of the recip mass. Because the rods rotate on the bottom and reciprocate at the top, the bobs are figured as some percentage of the total rod/piston assembly mass. That percentage is calculated on intended RPM usage and vibrational/resonant issues if known.

    [/ QUOTE ]

    Great stuff, learnt me something already today! /forums/images/graemlins/smile.gif

    Rene
     

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