Could someone please explain to me how these big stalls on torque converters work? people are always saying how automatics are much better at the track because you can get a more reliable runs and how you should put in a bigger stall but i dont understand this, and how exactly do you guys launch in an automatic, i doubt you do neutral drops so you must powerbreak it right?

I'm not a complete retard but i just never understood the whole Automatic part of in dragracing.
umm, i think thats its. I hope one of you can explain this for me because i'm tired of not understanding.

 

First you need to understand how a torque converter works. I won't get into the internal workings here. There are a lot of web pages explaining them.

A stock converter stalls around 1200-1800 rpm. The stall speed is the rpm that the converter stops slipping. All converters slip. If they didn't, the engine would stall at an idle like a manual transmission not stepping on the clutch. You can't physically increase the stall speed of a converter so you do it by buying a new converter with a stall speed close to what the engine wants. A manual transmission you just need to launch at a higher rpm before dropping the clutch. Having a high stall converter does the same thing. It lets the engine get higher in it's powerband.

A high stall converter will still work just off idle but it slips a lot more than a stock converter at those lower rpms. It slips to allow the engine to increase in rpm faster.

The stall speed of a converter is only an estimate. A 2500 stall converter in a mild SBC may only stall at 2200 rpm while the same converter behind a BBC may stall at 2800 rpm.

The only way to find the true stall speed of a converter is with a transbrake. That locks the transmission in 2 gears at once so the car won't move. The vehicles brakes can't hold back the amount of torque produced before reaching the converters full stall. My race car uses an 8" converter that stalls at 5700 rpm on the transbrake. I only launch at 3000 rpm.

In the old days before high stall converters were mass marketed, racers came up with their own ideas on how to launch an automatic transmission at a higher rpm. Someone came up with the idea of using a clutch. You used the clutch only to start and stop the vehicle. Once it was moving, the transmission didn't care how it was attached to the engine. Using the clutch allowed racers to launch at different rpms depending on their combination of parts.

 

alright, i think i understand the stall thing. but i still dont understand the launching part. So you lock your transbrake, then rev up your engine to your desired launching rpm just like a manual transmission then just release the transbrake?

 

If you really want to understand this you can call dave at Atlantic Coast convertors. He built my 3800 and I love it. 843-347-1320. He will go in much detail.

 

Well, most people don't have a transbrake but that's how it works. In a stock or mildly modded car the regular service brakes are strong enough to hold the car against the converter until the desired launch rpm is achieved. A stock 4L60E would never stand up against a brake anyway, the rear end might also break.

Rich Krause

 

...Stephen left out... torque converters MULTIPLY the engines torque output during the time the converter is going to its stall
rpm.

My current converter, while a mear pup compared to Stephens,
(4140 me) has a maximum torque multiplication of 2.77.
Now wether this is through the entire stall rpm range or not, I dunno.

You can have the converter maker put what ever T. multiplication you want in the converter. Mine is a 9.5" and I asked for the most torque possible, which at this time is 2.77. Converter maker said in 2004 Cadillac is coming out with stators that will allow a 3.01 multiplication.

If you watch a high stalled car leave versus a M6 you will see the advantage of a higher stalling converter. We don't generally have a bog problem.

 

Unless you put your converter in a stock car.

Which Caddies are supposed to the 3.xx STR? That'd be nice if it was in the new RWD car.