What stall speed and why

Discussion in 'D and C Extreme' started by R290, May 10, 2008.


  1. R290

    R290 High Wheeler

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    I thought this would be a good place to post this as you have built several rigs with auto's I've read from low to high and back to stock. So lookin for some real world input.

    For a 727 IH tranny, what is the best stall speed! I drive to trail and crawl on rocks?

    http://www.hughesperformance.com/xtm_xfm.php for light reading too :)
     
  2. Damian Grihalva

    Damian Grihalva High Wheeler

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    I've personally enjoyed 1800-2000 RPM stall on double-duty rigs. Even Rusty had one. These are not anything super special, relatively cheap and are readily avialable ($150ish) and all the way up to $300-400+ (Depending on how nice you want to go, the ones I use are normally somewhere in between). I rarely if ever recomend over 2200-2500 as there's just no need to go that high unless your racing.

    Conversely, I highly recomend you stay away from low-stall converters. They apply power way too soon and either make it difficult/impossible to stop or don't allow the engine to get in a good power spot to overpower big tires/crappy crawl/both.

    Not that you (R290) need this next part, but I think it should be said.

    Its a common MISTAKE to think because our IH motors have good torque numbers down low you should go with a low-stall converter to take advantage of those numbers. Not a single person here would attempt to drive up to some steps by simply letting your clutch out before slightly reving up your motor, so why would you get a coverter that does?

    I think its common to believe that 'High' stall converters don't apply power until high RPMs. Meaning, that if you get a 1800 stall converter, you need to hit 1800 RPM before you start rolling forward. In fact, IIRC, the 'Stall speed' is simply where the converter puts out its highest amount.

    High stall converters actually start applying power at a slightly higher RPM as stock converters do. In fact, depending on who you ask, the stock stall for an IH TF727 is about 1600-1800 (depending on motor and TC size). Getting a 1800-2000 RPM stall increases that by a mere 200 RPM.

    What does this mean? It means that your engine will rev slightly higher before you start really moving. Meaning, you'll still need to hold the brake pedal at a stop light, but it won't PULL until you get about 200 RPM more than you do currently.

    The advantage of this is simple ~ and few-fold.

    1) Its like slipping the clutch a bit. When you put your foot down, your engine revs into its power-band more before power is applied. Getting the motor up a little bit may not give much more torque, but the on the Horse Power side of things, it makes a bit difference. So you travel through the RPMs faster. So hard take-offs or high-torque starts are a little more impressive.

    I learned this lesson the hard way. My first scout ended up with 35" tires and 4.09 gears. GREAT on the highway, but off-road it lacked. While accending a steep hill (it was the lightest trail I've been on and stock scouts conquer it easily) If I didn't stay in the throttle, I would stop. I also had to stop a couple times for stupid kids not waiting their turns. Well, the point is, getting started was...difficult and annoying. I found that the difference between half and full throttle was a matter of engine noise ~ not that I'd get going any faster.

    You almost wanted to put it in nuetral and then drop it into Drive to get going (DONT DO THAT, IT"LL KILL STUFF). Anyway, Lil Mule (my first scout) would eventually start itching forward after a few seconds of full-throttle action, but I didn't like having to put it threw that.

    I found that the few hundred extra RPMs that a higher-stall converter would give was invaluable in times like that. It was the little edge that made things much more comfortable and made wheeling much more enjoyable. REMEMBER, this was NOT A HARD TRAIL.

    2) During daily driving. The nice thing about higher-stall converters during daily driving is most obvious when you need to get somewhere. The motor operating in its 'sweet spot' helps when navigating hilly areas, or if you need to step on it to get over into traffic/turn lanes. Most times they're be invisible during normal driving situations.

    3) FOUR WHEELERS. For more advanced wheelers, aka with higher crawl ratios, the high-stall coverters are required (in my book). Rusty had 62:1 crawl (w/ TC 126:1). That kind of crawl would easily over-power the brakes in drive. We've run into this several times with some of our buggies early and now I don't even mess with it. If you've gone with tera-low, or atlas, or worse, if you have a Klune AND Atlas (or any dual t-cases) having the engine in drive will over-power the brakes making it impossible to stop the rig without putting it in nuetral. I don't have to go into the safety problems of this senario (not being able to stop) ~ but regardless,

    In these situations, a High stall converter allows the engine to idle without really pulling. Meaning, You can sit in drive at Idle and only have to keep light preasure on the brakes ~ instead of hopelessly standing on them. Rusty was a great example, while driving down the waterfalls on Indy.

    When driving down 50"+ ledges, you're never too far from the brake pedal.
    [​IMG]
    (I get a kick out of the fact that I had to look through my cage's roof to see the spotter :eek:)

    Can you imagine being in this possition and not being able to stop?
    [​IMG]
    :sweatdrop::devil2:

    I think you can see my point. Now for the flip-side.

    The only draw back to higher stall converters is HEAT. The extra 'slip' generates heat. So make sure you have a decent radiator ~ or at least have one that functions properly. I DONT BELIEVE THAT A 1800-2000 stall CONVERTER WILL CREATE ENOUGH HEAT TO BE A PROBLEM. Remember, this stall speed is slightly over stock ~ kinda like using an RV cam to get more low-end power. Its enough to get some good effects, but not enough to cause poor driving.

    I had more to say, but forgot. Anyway, I'm not going to say that high-stall TCs are the only way to go. There are several theories and thoughts about what works and the 'how well' is up for discussion and arguement. Whose right and what's best is up to the end user's oppinions and experiences. But in my experience, 1800-2000 RPM stalls are a good middle-road stall that gives noticable benifets and few drawbacks. Which is why I use that speed almost exclusively.

    Hope that helps.
     
    Last edited: May 12, 2008
  3. CWB

    CWB Farmall Cub

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    Resurrection alert...I'm looking for a T.C. for my '78 Scout and can't find one locally. The counter monkeys at Auto Zone, OReilly's and Advance all say they're out of stock. Nothing at Napa either. Where's the best place to find one in the 1800-2000 rpm range? Part #? Source?
     
    Last edited: Nov 5, 2016
  4. kevingweq

    kevingweq High Wheeler

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    These folks are at the top of the food chain when it comes to torque converters , I wouldn't doubt that their products
    are re-branded at a big markup . I have installed at least 15 of their units -- No failures ,No problems ,
    Disclaimer -Never installed one in a rock crawler ,Most were in tow trucks and medium dump trucks , and of course coal rolling pickups
    in the 400-800 ft lbs range .
    http://www.precisiontorqueconverter.com/
     

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