Thread: Stall converter

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Originally Posted by sfort

What do they do and when do you need one? Just got my truck back on the road with more HP(425) turo 400 from a 78 suburban. My wife is grinning ear to ear I am a blessed man!

Many factors determine the need for a looser converter, among them rear tire size, rear gear ratio, vehicle weight, induction system, camshaft timing and so forth.

Let's say that you have a stock vehicle with the stock converter. It is matched by the engineers at the factory to be just loose enough to allow the motor to idle at a stoplight without pulling too hard against the brakes in gear and just tight enough to prevent allowing over-revving the motor on acceleration and wasting fuel. The stock camshaft is designed to make power from idle to 4000 rpm's or maybe just a tad higher.

Now, you swap the cam for one with longer timing. This new cam makes power in the motor from 2500 to 6000 rpm's, so there will be a dead zone from idle to 2500. With a stock converter that hooks up at maybe 1200 rpm's, the motor must pull through this dead zone, making little power and resulting in a slower car than you had with the stock cam in place. Also, the new cam wants to idle the motor at 1000 rpm's instead of 750 like the stock cam, so the motor is tugging at the brakes at every stoplight because the converter is up near its stall rpm.

At this point, a looser converter, one that stalls at around 2500 rpm's will be needed to deal with the longer cam. This new converter will allow the motor to idle higher without tugging on the brakes at stoplights and will also allow the motor to rev through the dead zone before the converter begins to stall at the higher rpm's. So, from a standstill, when you wood the loud pedal, the motor rpm's will flash up to about 2500, allowing the motor to be in the power-making zone and applying some real grunt to the drive rubber.

Converters are available in a wide range of stall speeds. A stall of around 3000 is generally considered by many to be perfectly acceptable behind a street motor, but much more than that is considered unfriendly on the street. Of course, a looser converter will make more heat, so that issue must be addressed with a cooler mounted in front of the radiator.

Thanks Tech! I need to get all the details about the engine rebuild and the truck. So far I am super happy with the way it performs. We have had the truck for a year and have just got it on the road (engine was sick when we got it). Worth the wait!

Originally Posted by techinspector1

Converters are available in a wide range of stall speeds. A stall of around 3000 is generally considered by many to be perfectly acceptable behind a street motor, but much more than that is considered unfriendly on the street. Of course, a looser converter will make more heat, so that issue must be addressed with a cooler mounted in front of the radiator.

You bring up many issues I am dealing with at this point with a TCI SSF 700R4 and, originally a 2600 or 2800 TC , now, a 1800. The more I research the more I understand what is happening to this tranny.

How do I know if the TC has Locked-Up and or Unlocked? I think the Switch is hooked to my Brake Peddle, the Brake light on the Dash comes on and goes off occassionally, but remains on mostly. I think I would like to have more control of the Lock-up, so does a manual switch make sense?

I think the fluid might be boiling in the tranny and causing my leaks, don't have a temp gauge hooked to it to find out temp of cooling going in and out of tranny, lines hooked into radiator, no external cooler (How much of a diff does it make?) Shouldn't the vehicles radiator keep the new Tranny at Operating Temp?

So many more questions,

Your knowledge on this subject seems to be ummmm, pretty good, I think you know what you are talking about more so than most Technicians I have spoken with on this Install, Thanks for any info you are able to provide.