What exactly is the stall speed? I always thought it was when the engine's rpms were high enough to get the car moving... but I've heard stock stall speeds are at 1800. And what's lockup too?

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89 iroc-z 305 tbi
everything stock, except for a mirror that fell off

 

Enkil,

Stall speed (or, K-factor as GM calls it) is the maximum speed at which the input shaft (pump) will turn before the output shaft (turbine) begins to turn. Theoretically, a torque converter with a rated stall speed of 1,397 RPM will allow the engine RPM to rise to that point before the turbine moves under maximum design load. By that theory, holding the brake and throttle to the floor in drive would only allow the engine RPM to reach 1,397, regardless of how much power the engine produces. Actual numbers may vary a couple hundred RPM due to inefficiencies and the different power outputs of engines. Many factory converters are rated at 1,397 or 1,611.

Another way of understanding the stall speed is to consider it the maximum amount of "slip" (for lack of a better term) that the torque converter will allow before moving. Under normal driving and moderate accelleration, the converter will not slip the full rated amount. Under heavy accelleration, the maximum slip will be achieved.

What this does in our cars is to allow the engine to operate at higher RPMs, where it produces more power, before the car even begins to move. The result is more powerful launches, faster upshifts at higher power levels, and hopefully better performance on accelleration.

A "lockup" converter is just as the name implies. At a given speed and engine condition as determined by the ECM, the ECM will operate a relay, which operates a solenoid valve in the transmission, which in turn closes a clutch pack in the torque converter. This action essentially "locks" the torque converter, or allows no slippage, just like in a standard transmission vehicle. Upon release of the throttle, application of the brake, or lowered road speed, the TCC (torque converter clutch) will disengage, once again allowing the converter to have some "slippage" as usual.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

And another thing....

The common factory torque comverter K-factors are as follows:

* K = K-85, 1,211 rpm
* G = K-100, 1,397 rpm
* F = K-110, 1,611 rpm
* E = K-115, 1,654 rpm
* B = K-140, 2,025 rpm

If you remove the inspection cover from the transmission/flywheel area, you might be able to see the paper decal (line RPO tag) that includes the code for stall. The second letter of the four-letter code is the K-factor.

The entire code scheme as I have it is as follows:

1st Digit = Transmission Application Code
* D = 1984-1/2 and up 700-R4, 4L60, 4L60E
* C = 1984 and earlier 700-R4, 200-4R, 200C, 325-4L
* B = 250C, 350C

2nd Digit = K-Factor (rated stall speed)
* K = K-85, 1,211 rpm
* G = K-100, 1,397 rpm
* F = K-110, 1,611 rpm
* E = K-115, 1,654 rpm
* B = K-140, 2,025 rpm

3rd Digit = Clutch and Damper Assembly Code
* C = (stock '86 'vette)
* H = (stock '94+ Impala)
* L = (stock '95+ L35 Vortec S10 truck)

4th Digit = Rear Cover Pattern
* C = 3 lug round pattern
* D = 3 lug round pattern
* E = 6 lug pattern
* F = 3 lug square pattern
* G = 3 lug square pattern

Hope that clears things up a bit.

------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0