So what parts, or combo of parts are altered to vary the stall from one to another ? I hear that there are different way to accomplish the same stall but the overall performance of the converter can be very different. If that's so what are the differences? Why would you want to choose a certain one for a certain application?
Good question. 1, First of all, as you probably figured, the smaller the diameter of the converter used, the easier it is to achieve a higher stall. 2, The impeller, or pump, as it's sometimes called will have a positive or negative fin angle. Positive means that the fins or vanes point in the direction of rotation, thus the throwing more oil towards the turbine, creating a lower stall. The opposite would be true for a negative pump. This is the primary means of altering stall speed. 3, There are several different styles of stator design . The various designs do have an effect on the stall speed, but their primary importance is to alter the torque multiplying characteristics of the converter. Without this part in place or with a broken sprag, you now have just a fluid coupling,..not a true torque converter. 4, The actual clearance between the pump and turbine, or stator clearance, also affects the stall , but is not an efficient way of changing it. It is just a fine tuning technique. If you were to lose a thrust washer or bearing ,the stall would go up a bit , but you'd know it before long because the parts would end up in the transmission and create havoc there before long.
Are these a correct way of looking at some of the aspects ? Roughly 2:1 torque multiplication when the movement of the out put or stator starts moving, rapidly decreasing in ratio towards 1:1 the closer the speeds of the input and out put are to each other. At the RPM point motion starts - that is the "stall" ? Terminology because the movement is "stalled" upto that RPM set point. Having a converter reach its stall point near the same rpm that your engine develops its torque.... Better above or below the engines torque curve ? Is it beneficial to prolong the multiplication phase thru the rpm range or get things coupled as soon as possible? If its prolonged it that know as "LOOSE CONVERTER" The methods of changing stall that you briefly touched on, how do they (searching for correct word to use ) change, perform, efficiently, transfer power, in normal driving.
Best stall convertor of all....a CLUTCH!!! Variable rpm stall from idle to WIDE OPEN!!! If the traction is limited let 'er out easy n early, traction is good wind 'er up n drop 'er!!! Shift on....... Sorry guys just had to do this!!!
Yea, but there is no torque multiplication with a clutch. Infinitely adjustable coupling solely up to drivers discretion and input. Also if you have got a bad left leg, its not that much fun.
Torque is over-rated!!! Nuthin better than 8,000+ rpm small block screaming to go.... again, just ribbin ya guys. Can't ya just put the clutch pedal on the right?
Be realistic with the torque multiplier thing. It does so at the expense of something else - you can't create energy or else you'd have a perpetual motion machine.
Good thread, and a good explanation of variables posted above. We've used Coan, Neil Chance, and now with the twin turbo car Pro Torque converters. All the best, and each has their own theories. Trial and error to find the best one for your car. Whats impressive to me is the Pro Torque only has 1% slippage at the big end. And thats with a lot of horsepower.
I'm not the builder, but as far as I know there is a realistic multiplication of torque that's nearly 2:1 at the end of the stall cycle and beginning of the acceleration cycle. It diminishes rapidly proportionate to the rate of acceleration headed toward 1:1 at the coupling cycle. Maybe that's FOS but that's what I hear. What you give up is heat, and massive RPM on the motor while the trans is catching up.
Some very good explanations on how the converter works . Lots of great information too . I am sure there is a lot of people out there that had no idea on how or what the trans converter did to make the car go . Then on the other hand why there is so many different converters to choose from for the engine you might be using . On the other hand , a clutch is entirely different from the way the torque converter actually works . With the higher stall of a converter the rpms from the engine can be higher before the converter actually locks in to make the car go . With a clutch , all you are doing is making the clutch disc slip between the flywheel and pressure plate . As we all know , a slipping clutch is not a good thing ! I have used a clutch and a high stall converter for racing and when it comes to big HP engines with big cams , the stall converter is the best way to go ! With the big stall you get the rpms up to where your cam works the best so you have the cams power band working already to go when you take off . A clutch will not work that well and you have more slippage and less traction being put to the ground at the take off . Thank plain sucks ! personally I still LOVE a 4 speed trans ! Personally , there is nothing better than banging gears as you go down the road ! Just my opinion . Retro Jim
Sorry, I skipped school yesterday. True stall speed is the maximum RPM attainable at "WFO" throttle.(That's a technical term LOL ) .... with the output shaft locked with either a trans brake or darn good shoes or pads. Flash stall is usually pretty close to that number, but a lot harder to read accurately. With a stock or fairly low speed converter, you should be able to hold the brakes and check it with the engine tuned up, warmed up for max power. A high stall converter in front of a manual shift automatic trans can be checked in high gear with the brakes locked and UP ON JACKSTANDS. Yes a maximum effort converter should be set to stall right at max torque or maybe 200 rpm higher. You want to leave the line, multiplying all the torque you have. Some stator designs have a big arm in them ,multiplying torque at 2.4 to one, almost violently, but then it diminishes real fast...while others have less of a multiplying effect but over a much broader torque range. Again ,you're dealing with a fluid coupling, so all of this stuff is brought about through experience and trial and error. You can't just multiply your first gear ratio times your rear gear to find the overall starting line ratio...like you do with a stick shift car.. It's a lot more complex than that.
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