I keep seeing posts about people upgrading their torque converters. And I see them sold in Jegs/Summit. But what the heck does it do differently? Would I know it if I happen to already have one?

 

Here's a quick answer, all I have time for. It is a fluid filled hydraulic clutch that has contra-rotating impellers in it. Most stock convertors are designed to "engage" at about 1000-1300 rpms. When people talk about having a 2500 rpm convertor they mean that you can "torque" the engine up to 2500 rpms before the convertor starts to transfer energy back to the transmission. This was not a strictly technical description, just a quick and dirty response.

 

A stall converter is a torque converter that slips more than stock. The stall speed is the speed at which the converter will become one-to-one and will "stall" the engine.

Here's the basic theory. A converter has two fundamental pieces (impellers). One spins one to one with the engine. The other is one to one with the transmission input shaft. The engine side is called the drive side and the trans is the driven. As the engine increases rpm, the drive impeller "throws" transmission fluid against the driven impeller. As rpms continue to go up, the force applied to the driven impeller is increased until the rotation of the drive and driven are one to one (well almost except in a lock-up converter).

All converters have a stall speed and are thus a stall converter. For hot rod purposes, a stall is considered a converter with a stall speed greater than stock which is usually around 1800 rpms. That is where the one-to-one relationship is obtained.

The purpose of a stall is two-fold. One is to allow the engine to rev up higher while power braking so that launch takes place within the power range of the engine. The other purpose is for those who install monster cams with a lot of duration. If a cam has a lot of duration, they won't idle below say 1000 or 1500 depending on the cam and engine because a lot of duration doesn't produce a lot of vacuum. Well, when you drop the car in gear, a stock converter will drop the rpms of the engine to the point that it will not run. So a stall is used to enable you to increase in gear idle speed.

Hope this helps. I'm sure others will chime in.

dl


[Modified by dladd74roadster, 3:26 PM 5/10/2002]

 

Yip.


[Modified by James, 3:25 PM 5/10/2002]

 

I'm guessing my engine has been cammed but still has a stock converter. She's a dog at idle! A mechanic thinks my engine has been rebuilt (#'s match) because the paint looks good. And I'll guess there's been a little tinkering inside... :smash:

 

Here's enough info to give you a good headache, it's from Bow Tie Overdrives but I'm sure you can apply it to other trannys. http://www.700r4.com/Tech/TCC/introindex.htm

 

A real simple answer is if you have a hotter cam your car would have kind of a slower take off. If you have higher stall converter say a 2500 stall it will allow your car to get in a higher RPM for a hard/fast take off.

My car has a stall converter rate between 1800-2200 RPM, If I hold my brake on real hard the car don't move and the transmission doesn't kick-in (lock) untill 1800-1900 RPM. The down side is my car doesn't really make much HP until 2300 or higher RPM. So this means my take off aren't very good and the tires sometimes don't spin (old men on canes/children on power wheels pass me).

Once I get a higher stall hopeful it will allow my engine to hit it power band and launch me hard (tires spin, smoke, earth rotation slows down temporary :crazy:)