Teach me about torque converters
11-10-2009, 10:23 PM
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Teach me about torque converters
Hi all,
I'm fairly new to this domestic sports car thing. Always played with forced induction 4 cylinders up until now, and in that world.... standard transmissions are the way to go.
I've read up a bit on torque converters, and the different stall ratings (brake, true, flash stall) and how torque converters work.
What I dont understand is this: I've seen it on two separate occasions. 1 very very built foxbody mustang, and one 454 pickup. Both of them, when they took off, would stall to the moon. I'd guess 3500rpm or better. And wouldn't move an inch. Suddenly they'd catch, and lurch forward so hard that they would break traction, and squeak the tires, just a touch. Why is this? What causes this, and what is the benefit of this? The driver's were not racing anyone, not in a hurry, and didn't smash the gas. The rev's came up slowly, and smoothly.
Infact, the 454 pickup, his tires squeaked several times. He was creeping up to a stop sign, and was several cars back. So each time he moved forward, the rpm's would rise, quite high, and then finally it's catch, and the truck would squeak the tires and jump forward.
Why is this?
I'm fairly new to this domestic sports car thing. Always played with forced induction 4 cylinders up until now, and in that world.... standard transmissions are the way to go.
I've read up a bit on torque converters, and the different stall ratings (brake, true, flash stall) and how torque converters work.
What I dont understand is this: I've seen it on two separate occasions. 1 very very built foxbody mustang, and one 454 pickup. Both of them, when they took off, would stall to the moon. I'd guess 3500rpm or better. And wouldn't move an inch. Suddenly they'd catch, and lurch forward so hard that they would break traction, and squeak the tires, just a touch. Why is this? What causes this, and what is the benefit of this? The driver's were not racing anyone, not in a hurry, and didn't smash the gas. The rev's came up slowly, and smoothly.
Infact, the 454 pickup, his tires squeaked several times. He was creeping up to a stop sign, and was several cars back. So each time he moved forward, the rpm's would rise, quite high, and then finally it's catch, and the truck would squeak the tires and jump forward.
Why is this?
11-11-2009, 12:53 AM
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Re: Teach me about torque converters
Both of them, when they took off, would stall to the moon. I'd guess 3500rpm or better. And wouldn't move an inch. Suddenly they'd catch, and lurch forward so hard that they would break traction, and squeak the tires, just a touch. Why is this? What causes this, and what is the benefit of this? The driver's were not racing anyone, not in a hurry, and didn't smash the gas. The rev's came up slowly, and smoothly.
It also sounds like they were trying to do a neutral drop. Neutral drops in an automatic transmission have a tendency of breaking transmissions. Automatic transmission work off hydraulic pressure. It would be the same as using a manual transmission. Leave your foot off the clutch, bring the rpms up to 3500 rpm and pull the shifter into gear and see what happens.
To launch at high rpm with an automatic transmission, you need a tranny brake. It allows you to launch up to the converter's stall speed. You put the transmission into first gear and push the transbrake button. The transbrake applies pressure to the reverse circuit and since the transmission is already in first gear, it locks the tranny so no power reaches the output shaft. This allows the engine to reach the converter's stall speed. When the transbrake button is released, the reverse circuit fluid is dumped and the vehicle launches forward in first gear. Even though my converter stalls at 6000 rpm, I launch at 4500 using a 2 step because that's roughly where the engine makes peak torque.
If you want information about torque converters, check out these pages.
http://www.hardtail.com/techtips/torqueconverters.html
http://www.hardtail.com/techtips/sel...converter.html
http://www.hardtail.com/techtips/converter%20stall.html
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