I'm planning a top end mod, and when I inquire about a cam, I'm ask if am planning on keeping the stock torque convertor. I have a TH400, w' 3.36 rear-end. I planning a CompCam XE262H. that's been recommend for my set up. Why would cam change the stall and how. What's the symptoms if not matched correctly.

 

More peolpe that know will chime in, but the higher stall gets the motor into higher RPM faster where the cam has its power ban. It will also help with idleing with a big cam.

 

I read that article few days back when I was shopping for a new TC, its very simple and will help you understanding that "mysterious" subject.

http://www.hardtail.com/techtips/sel...converter.html

 

Good article here:


http://www.chevyhiperformance.com/te...yno/index.html
and here:
http://www.rodandcustommagazine.com/...ers/index.html

 

I have the same cam (XE262H) in my engine and I can tell you that changing torque converters to something around 2,500 rpm stall will make a dramatic difference in performance. I'm talking about standing start acceleration. This is especially true if you're keeping the 3.36 gear. If you are just going to punch it while you're rolling, then it won't matter.

 

just to be sort of clear, Cam does not affect stall speed, that is set in the converter and it is the speed at which the converter locks up. Meaning it is like a clutch and when locked it is not slipping at all, same rpms going out as coming in.
Where cam and stall are related to each other is in matching stall lockup speed and power band on the cam. Your lockup speed should be inside the power band on the cam, I think just before peak power, but that part is a guess.

 

Stall speed (brake stall) is that rpm attained by the engine when the output of the converter is locked, in other words, the input shaft of the transmission is not turning. The latter can be with the foot brake fully applied and held (providing the rear wheel brake has enough torque to resist), or if the transmission has a trans brake which applies internal clutches to "lock" the transmission such as used with race transmissions at the drag strip.

The stall speed is affected by anything which changes the torque curve of the motor, or by changing the characteristics of the torque converter, such as diameter, changing the positive or negative characteristics of the pump, the clearances, the stator design, or the turbine. Unless the converter is cut open and altered, the characteristic of the converter doesn't change, but the brake stall speed can be changed.

An example of a different stall speed will be seen by comparing the brake stall speed of a converter by using a 4 or 6 cylinder engine, and then substituting a BBC. The greater engine torque will allow more rpm before the converter can hold the greater engine torque.

In the case of a camshaft change, if a short duration cam results in a brake stall speed of, say, 1800 rpm with a tight stock converter, and then a long duration high performance race cam is installed, the stall speed will actually decrease because the engine makes less torque at those very low rpms.

Alternately, if a loose high stall "race" converter (for example, less than 10 inches in diameter) is used with a mild engine having a short duration "economy" cam, the engine torque will drop rapidly above 3000 or 4000 rpm and the converter stall speed may be only 4000 rpm; but if the cam in that engine is changed to a race cam with a torque peak near 4000 rpm, the stall speed will be greater because of the greater available torque at that higher rpm.

Conclusion: Published stall speeds are approximations and may be higher or lower that you will actually experience, depending on your engine's torque output which is, in turn, affected by displacement, cam choice, head air flow, induction and exhaust efficiency.



Converter brake stall determination...
With a clear road ahead, apply full brake pedal with your left foot and HOLD, and then quickly apply full throttle and hold for about 2 seconds while watching the tach. This is your stall speed. CAUTION: Some combinations can over power the brakes and move the car forward as they can't hold at full throttle; also, don't do this for more than a couple of seconds as the transmission fluid will become hot rapidly.

 

Thanks for all the great info. and articles. I have a much better understanding of the torque converter. KBbroiler, I see you have a 383ci. engine setup. My plans ( as they have been changing) are L48 with RHS cast iron heads 64cc chambers & 180cc runners ,CompCams XE262H. Should I step down the cam to XE256H. I see it come's on earlier, and has a lower stall speed. Or will I be safe with the XE262H. Thanks again for your help. Bruce

 

I think you will be OK with the 262 cam, as long as you upgrade that converter.

 

Larrywalk presented a great explanation of how stall speed is affected by engine performance. In actual practice, each engine configuration (varying horsepower/torque outputs) requires a different torque converter design to provide the proper 'match'. If you have a standard torque converter for a 'base' 350 Corvette engine and you beef-up the engine, that same torque converter is going to have a higher stall speed [because of the increased HP being presented to it]. Replacement torque converters should provide a table of stall speeds at varying HP inputs so you can select the proper unit for your needs. That's why it's best to call the converter manufacturer to have them help determine the proper unit for your car when you modify an engine.