2500 rpm stall

[Saltshaker]

can someone explain what this means? I want to put a C6 or C4 in my car and this converter was recommended. How is it different then the stock converter?
Does TCI make a good transmission?
Jon

[GerryP]

It means the torque converter will theoretically allow the engine to reach 2,500RPM before the engine "stalls" and RPM will not increase beyond 2,500RPM.

The stall speed depends upon variables that influence the stall speed.  Engine torque affects stall at the front end and vehicle weight and rear gear ratio affect it at the back end.  And unless you use a trans brake it's unlikely you would reach a rated stall speed.  This just means that rated stall speeds just allow you to roughly compare one converter against another.  It's not quite that simple, but you have to start somewhere.

What it means for you, though, is that the engine will be able to get into a better part of the torque curve to help launch the vehicle.  So, for instance, if you had a cam that started to get into its torque band at 2,500RPM, you'd have more torque available at the instant of launch than if your converter stalled at 1,600RPM.  That doesn't mean much if you're not drag racing but a looser converter can make a vehicle with a bigger cam a little easier to drive.  Such as not pulling through the brakes while waiting at a traffic light, having a smoother takeoff from a stop light, having a higher idle rpm to help with engine vacuum or idle stability.

I have nothing to offer on the quality of TCI transmissions.  You can spend more but you just never know, really.

[plovett]

A stock torque convertor will stall in the 1200-1800 rpm range.   That means whenever you hit the gas it will go to roughly that rpm. It won't go higher until the vehicle picks up speed and allows the rpm to increase.  It is analogous to slipping the clutch with a manual transmission and then letting it fully out (engaged) at a certain rpm.  So going to a 2500 rpm convertor means that you will get that much more rpm which means you will have more power to use.  It is a form of torque multiplication.  More rpm for the same wheel speed. 

Above the stall speed, the convertor "locks up" and stops slipping.  However, that is misleading as a convertor never fully locks up unless it is a true "lockup convertor" with a clutch built in.   Clear as mud?  Well, a 2500 rpm convertor will give better performance than a stock convertor, especially with a mildly modified engine.  A more highly modified engine will want a convertor with a higher stall speed because the engine is designed to run at higher rpms.  But you don't want a higher stall speed than necessary for the engine and vehicle combination as that would mean the convertor is slipping when it doesn't need or want to.

Just like a clutch in a manual transmission you have to slip it to get it going, but you don't want it to slip too long or you will waste energy and increase wear. 

Further muddying the waters is the fact that torque convertors don't really have a set stall speed.  A 2500 rpm convertor, if it stalls at 2500 rpm with your combination (at max throttle and load), still won't always slip until 2500 rpm.   At lower throttle and loads the convertor will only slip to a lower rpm.  So you can cruise around town at lower than the rated stall speed with little slippage. 

I'm not sure if I am explaining it well.

paulie

[CV355]

GerryP and Plovett explained it well.  Stall speed is a rough estimate of how much "slippage" you get until the drivetrain is in sync.  It's a fluid clutch.

2500rpm isn't a bad stall speed.  Just don't make my mistake from 10 years ago and get something drastically over-stalled for the street.  I had a 3800rpm converter at one time and it made driving around town rather difficult.  It would function, but low-throttle response felt somewhat unpredictable, like if you've ever had a transmission run low on fluid and slip constantly.  It was amazing for the track, but awful on the street.

[Saltshaker]

Thanks for explaining
Jon