Question on torque converters

[Joseph E.]

Can someone enlighten me as to what the "stall speed" of an automatic transmission torque converter means? Would a worked turbo 400 trans with a 4500 stall anti-balloon converter be too much for street use? How or does stall speed affect street driveability? Thanks.

Joe #45420

[Paul J.]

Re: Question on torque converters

From what I know of the subject your engine would have to go to 4500rpm before the slipping (and heating) stops and the converter is fully locked. Stock units are about 1800rpm and you can watch your tach to see when the car starts moving.

[Joel A.]

Re: Question on torque converters

A 4500 rpm stall converter for the street would be waaaaay too much. Stock stall on most automatics are around 1200-1500. A lot depends on the torque the engine creates.
The stall speed is the rpm at which the converter is actually working to move the vehicle against a load(vehicle weight, etc). At 4500rpm, you're engine is already probably at the top of it's peak torque output, which would be good if you are racing, and running 4.11 or lower gears. However, the higher the stall speed, the higher the internal temps are. Running high stall converters on the street creates tremendous heat inside the trans...basically a death sentence.
2500rpm stall is about the max I would recommend on a street driven car. The factory, "hi horse" automatics came with 2500 stall converters...this allowed for the lumpy cams, since a lower stall speed would usually kill the engine as soon as you put it in gear, or it would chip the tires when you put it in gear...neither was/is acceptable.
hth.

[Duke W.]

Re: Question on torque converters

It's easy to determine stall speed. At a dead stop step hard on the brake pedal, floor the throttle and read the tach. It only takes a couple of seconds and will not hurt anything.

As stated a 4500 stall converter would be totally unsuitable for road use as would an engine that requires such a converter - one with a torque peak of 5000-6000 revs and a power peak up in the stratosphere. Such a combination would be good for drag racing, but terrible for road use and get 5 MPG because the converter would always be slipping a significant amount - dissipating the engine's power by heating up the trans oil.

As stated, base Corvette engines typically have about 1800 RPM stall converters and 85-90 percent of peak torque at the stall speed. Such a combination is very responsive in normal road use and gets decent fuel economy.

Duke

[Joseph E.]

Re: Question on torque converters

Thanks to all those who replied to my inquiry. I have a better understanding now of how a converter works, however, I still have one more question. Would street driveability be improved if the previously mentioned set-up ,a worked T-400 with 4500 stall converter, had the converter switched out to say a 2000-2500 stall unit? This trans is in a prostreet big block car that I'm considering looking at and possibly purchasing. I'm guessing that it would make the car more manageable on the street and reduce heat buildup in the transmission while putting the "lock up" of the converter way below the peak torque producing rpm of the engine. Information provided by the members who respond is always highly valued and appreciated. Thank you. Happy Thanksgiving to all!

Joe #45420

[Stewart A.]

Re: Question on torque converters

Joseph you need to know what RPM your cam shaft starts to produce some snott. My cam in my Mustang comes in around 3500 rpm so that's where my stall locks in at. I originally had a standard converter in the car and it was yuk ! Below 3000 the car is just a not on song. So I put a 3500 in and it now puts me in the backseat when I let it rip. It's kind of like having a clutch in first gear. My Misses drives it all day with no problem it putts around town and when I get in it I clean the plugs out pretty quick. If your cam is not to big and only a couple of sizes up on standard running a big block should make heaps of snott down low so you might be able to get away with a tighter converter maybe 2500. You really need to know what your cam shaft specs are so you know when your Cam is coming in. Stewy