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Torque converter choice

Discussion in 'The Garage' started by shockline, Mar 27, 2007.

  1. shockline

    shockline Registered Member

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    At the recommendation of the site adm, I am starting a fresh post on an old topic.

    I am working on converting my 1984 K5 into something more useful than it is. It has to pull my 20 ft boat, but I want to have other types of off road fun as well.

    I got a 383 stroker with around 425-450 hp, the cam power range is 3500-6500, I have a turbo 350 trans, and 3.08 gears (for now).
    My engine builder is suggesting a B&M hold shot 3000, but others disagree.

    I have until this Friday to buy and have it installed, so any advice would help. I know nothing about converter performance with 4X4's
    Thanks:wink1:
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I know this isn't answering your question, but one thing to keep in mind is that the power output of the engine is directly related to stall speed. The same converter that stalls at 1500RPM on a bone stock 305 will stall at a higher speed behind a more powerful engine.
     
  3. shockline

    shockline Registered Member

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    Thanks, I had not thought about that. My so called stock converter is a rebuilt out of a 1975 suburban with with a 350 eng and trans. I wish I had a local 4x4 buddy with a converter so i could take a ride, i am afraid that by the time i know if i like my choice or not I will be stuck with it. After all free is free, but the new one is $400.
    I got a guy from a trans shop telling me to go with at least a 3500 stall and I already was afraid of the 3000 one.
     
  4. resurrected_jimmy

    resurrected_jimmy 1/2 ton status

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    I think a 3000 rpm or higher stall will not work well in a towing application. I am by no means an expert on torque converters but any I have seen listed for towing usually stall at very low rpm's
     
  5. Speedo

    Speedo 1/2 ton status Premium Member

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    It sounds like you are trying to compromise in too many ways to make a really good choice on what converter to use. For towing it would be more desireable to have a high torque engine with lower gearing. For towing you don't want a loose torque converter because it will create more heat. With your gearing/engine combo it doesn't sound like you should use a tight torque converter because it will pull your engine out of the rpm range where it will work efficiently. Lastly if you are running taller tires it only makes things more difficult. I would make sure that you have lots of capacity for your tranny cooler and talk to your engine builder again with what you are planning to use your Blazer for.

    Gus
     
  6. shockline

    shockline Registered Member

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    So far I have a set of dual electric fans and two tranny coolers. But you are correct that I am trying to put too many uses into one truck. My engine builder does drag cars not trucks so that is one reason i am desperately seeking someone that has an oversized converter, but so far the ones I have seen listed in the old post had 1/2 the stall that I am looking at.
     
  7. Brians89K5

    Brians89K5 1/2 ton status

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    A 3000 stall will be a pain to tow with. You want something that stalls down low around 1500 to 2000 RPM. It will make it more of a joy to drive. With a 3000 stall it will be like you are launching your truck out of the gates everywhere you go. Like a drag car. I had a trans am with a 2500 stall and I couldn't imangine having to tow with it. Get a factory lock up and enjoy the torque of your engine.

    ~Brian
     
  8. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Here is some reading for you as well.

    http://www.hemmings.com/mus/stories/2006/02/01/hmn_feature23.html

    http://www.hemmings.com/mus/stories/2006/03/01/hmn_feature1.html

    Knowing exactly whats going on, how they operate, and how changes affect your choices and performance will help you make an informed decision about what you want.

    As Gus mentioned, you can't compromise everywhere, or you come up with a completely unworkable drivetrain. You could put a stock converter and 4.10 gears with that 383 in your truck, and likely be faster and definitely tow better than you can with a high stall converter, 3.08 gears, and 33" tires.

    You also need to consider matching your engine RPM where you will be towing to where your engine makes power. To put your engine into the power range of your cam, with those tires, gears, and tranny in drive, you'd need to be going 112MPH, give or take. Second gear would net you 65MPH again at 3500RPM. Not many people like listening to an engine run at that RPM, but that's what you are looking at.

    Don't forget though, that you can't just compensate by using a different transmission gear...numerically low gear ratios make it hard to get a vehicle moving. That is exacerbated with an increased load, such as a trailer. This is why the new diesels are designed to make incredible amounts of torque down low. But the rear gearing STILL matches what they intend for the truck to do. You don't see tow rigs with 3.08's.
     
  10. Thunder

    Thunder 3/4 ton status

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    Ever thuoght about changing the cam? IMO a cam like yours is about useless in anything but a drag car or a mud bogger. It is a terrible choice for a 4x4 off road and tow rig. Espically with 3.08 gears:eek1:
    You need low end torque for both off road and towing. That 3500-6500 cams powerband is way way above normal towing or offroad use. At freeway speeds towing your boat you wont even be in that cams powerband. You will get horrible gas MPG and have no pulling power at normal speeds in high gear.
    Most tow & off road trucks work best with cams in the 1000-5500 range.
     
    Last edited: Mar 27, 2007
  11. shockline

    shockline Registered Member

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    Those articles are good, now I at least know how they work. Thanks.
     
  12. NateInChandler

    NateInChandler 1/2 ton status

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    your gonna smoke the trans with 3.08's and a 3,000 stall... especially with anything more than stock sized tires... i would go with a nice tci 2400 stall or a hughes HD2000, they both will stall a little more than advertized because your vehicle is heavier and has a good amount of power with the wrong gears, make sure you go with a good trans cooler also.. should stay happy for awhile... nate
     
  13. shockline

    shockline Registered Member

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    If I give up the dreams of rock climbing and steep trail riding, can I make my high rpm cam and trans work for drag racing and pulling the 20 ft boat once in a while? I have come to realize I will have to have different gears for sure, the motor is assembled and short of paying for a new cam again I think I am going to stay with the one I got for now. All your advice on the converter makes me think I need to go with a lower stall due to the size/weight of the truck plus the 383 should have lots of torque to begin with.
    Thanks to all that took the time to give advice I really appreciate it.
     
  14. NateInChandler

    NateInChandler 1/2 ton status

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    no problem man, if you dont ever wanna rock crawl or tow again, a little bit more stall depending on the specs of your cam and other things would prolly help ya a little bit, but stay on the small side, too much stall and your just revving a motor that was designed to make torque anyways.... Nate
     

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