Can someone help explain the concept of a torque/stall converter to me. I'm trying to learn how they affect the drivability of a vehicle, nothing in depth.

Thanks.

 

A torque conveter is just a fluid clutch that uses fluid to move vanes ( like an old water wheel on a stream) in a housing. The converter is set up much like a clutch in that one part is bolted to the engine and one to the transmission. Like with the clutch pedal is pressed to the floor , the clutch dissengages the transfer of power to the transmission
At engine idle the torque conveter has a set rpm that , in general term dissengages the transmission of power , like pushing the clutch in. When the engine throttle is pressed and engine rpm rises to the designed rpm the fluid is thrown against these vanes and transfers power to the tranny and ultimately the rear wheels and you move.

This is the most basic I can get. But like your own car you need only a little increase in rpm to start your car moving. To low a stall and the engine dies , like not pushing in the clutch when coming to a stop. Or to high a stall rpm or stall speed reving the engine rpm and 'popping' the clutch.

Race cars or drag cars inparticular have a different purpose than you mom's sedan.

The term stall describes that pre deterimed or designed rpm when the fluid engages the vanes and begins to transfer power with the tranny in gear and the brakes locked.

Now a hi performance stall converter is designed with a higher rpm to take advantage to the best hp/torque to launch a particular car . Just as you would rev the engine with a clutch before leaving the starting line to maximize the power your engine developes.

Your passenger car converter stall is probably between 1200 -1600 rpm . Where a stall convert will be 2500-3000 rpm and up depending on many factors . This is basilcy determined by many factors including engine , differential ratio, transmission, total weight of the car.

I'm not a teacher but thats a nut shell, I'm sure the internet or other will clearify and be more specific.

 

that pretty well nails it!


when camshafts with mega lifts/overlaps, carburetors with large diameter venturies, and headers with large diameter primary tubes are combined you get a great recipe for top end horsepower and torque but you get killed on the bottom end. to raise the launch rpm into a more useable range a higher stall converter is used. for everyday driving the stall converter causes the sensation that the transmission is slipping on take off, more heat is generated in the fluid, and fuel mileage suffers.

todays roller cam profiles and electronic fuel management systems lessen somewhat the effect on driveability unless gone to extremes.

 

Thanks a bunch, that's what I assumed it was but I wasn't sure.

 

 

Very informative write up. Thank you

 

as perfect an "automatic clutch" description as I''ve ever read

You've left out the added mechanical advantage the converter gives (and maybe you left that out intentionally - part of your basic description). This is the "STR" value given to converters.

The stall value is when (RPM) the automatic clutch grabs; the STR value is the mechanical advantage the converter provides at lower RPM's (then slowly takes it away as RPM rises).

 

And while you're looking at converters, the higher rpm rating the looser it will be. But STR also plays a role. The lower the STR, the looser it will be.

But there are trade-offs. Obviously with rpm, the higher you start to go the better the potential performance if you have the right tires/traction. But the car will become looser/sloppier at low speeds before the converter locks.

As for STR, a higher STR will be tighter as well as perform a better launch, but the lower STR will be looser and will be more efficient all the way down the track.

I personally have a Vigilante that flashes to 3200 rpm and has an STR of 2.5

It is a little loose but bearable. I would suggest finding one to test drive if you plan on a 3000rpm or higher converter. Some people say they drive like stock, but different folks have different tolerances. I would not recommend my converter to anyone with 3.42 gears or milder without a test drive first.

 

If I have the stock Z51 gears, and don't want to do too many drive train modifications, how big a cam can I go? I was looking at the G5X3 but I understand that to be a bigger cam.

I'm more interested in roadracing/autoX and I know I really need a manual transmission, but that will come in time. How detrimental will a higher stall converter be in those types of races?

 

Since a hi-stall will always allow your engine to run in a good RPM range, I would say it will be an advantage as you accelerate out of each corner. The improvements in the new hi-stalls are great and the very few people I let drive my car say they do not notice the stall at all. Mine will lock up about 40 MPH and in regular driving seems almost stock. It will unlock with very little throtle tho.