Torque converter stall speed

[Jack H]

I’m building a 512 stroker for my 73 challenger, it will have apx 550 hp. The 440 I have in it now is 350 hp.
With 3.55 rear end and a gear vendors over drive I’m running 2200 rpm at 70.
What stall speed converter should I use? A Hughes HUG SEH2832BL-10 flat tappet cam
I have power brakes and a/c

 

[Katfish]

Set up a spreadsheet and see where it falls.
You might be ok with what you have, since the only variable is the increased torque. Whatever stall you have now will be increased.

More HP/torque will increase stall speed
Heavier the vehicle, the higher it will push the stall
Lower gears, such as a 2.73 or 3.08 gear, will increases stall

The mathematical constant that defines a converter's stall speed (in rpm) is called the "K" factor
K is the observed stall speed of the converter divided by the square root of the applied torque
The relationship is expressed mathematically: K = RPM/torque^0.5

Once the K factor for a converter is determined, the stall can be predicted for different torque values

Let’s say your engine creates 500 ft-lb of torque at your converter stall of 4,000 RPM.

The square root of that is 22.36. If your converter stalls at 4,000 RPM, you divide 4,000 by 22.36, and you get a K-Factor of 178.89.

If you increase your torque to 550 ft-lb, by reverse calculating the equation related to the same torque converter and K-factor, you can predict your stall to be 4,195 RPM.

 

[Jack H]

Set up a spreadsheet and see where it falls.
You might be ok with what you have, since the only variable is the increased torque. Whatever stall you have now will be increased.

More HP/torque will increase stall speed
Heavier the vehicle, the higher it will push the stall
Lower gears, such as a 2.73 or 3.08 gear, will increases stall

The mathematical constant that defines a converter's stall speed (in rpm) is called the "K" factor
K is the observed stall speed of the converter divided by the square root of the applied torque
The relationship is expressed mathematically: K = RPM/torque^0.5

Once the K factor for a converter is determined, the stall can be predicted for different torque values

Let’s say your engine creates 500 ft-lb of torque at your converter stall of 4,000 RPM.

The square root of that is 22.36. If your converter stalls at 4,000 RPM, you divide 4,000 by 22.36, and you get a K-Factor of 178.89.

If you increase your torque to 550 ft-lb, by reverse calculating the equation related to the same torque converter and K-factor, you can predict your stall to be 4,195 RPM.

Thanks that’s great info. I’m trying to find the sweet spot with enough vacuum at idle for brakes and a/c and not having too much slip in OD.
I’ll have to do the math in the morning when I’m fresh.
Thanks for the help

 

[Katfish]

I don't think the TC will affect the vacuum.

Numbers below are probably closer to what you're starting with and heading to.
Factory converters are typically 1800-2500
And (ballpark) you'll be going from 350 to 550 on the torque?

Torque Stall K
350 2500 133.63
550 3134 133.63

 

[Chryco Psycho]

The other way to look at it is you need the cam to be its power range Before locking the converter
So for example if the cam starts making power at 2600 rpm I would use a 3000 stall .
the other factor is a cam rated for 2600 rpm will make power sooner in a 512 than a 383 so maybe 2300 rpm so a 2600 stall should be fine .

 

[Ricks72Chlgr440]

I’m building a 512 stroker for my 73 challenger, it will have apx 550 hp. The 440 I have in it now is 350 hp.
With 3.55 rear end and a gear vendors over drive I’m running 2200 rpm at 70.
What stall speed converter should I use? A Hughes HUG SEH2832BL-10 flat tappet cam
I have power brakes and a/c

Your engine will be a torque monster, so you won't need a high stall converter... especially for the street. Your issue will likely be having enough tires to hold the car to the pavement! Power is useless unless you can get it to the ground!

 

[Xcudame]

Katfish nailed it! People run out and buy expensive torque convertors all the time when building big torque motors when they could have used a slant 6 convertor that everyone thinks is a dog. For certain years, the slant 6, 340, 383hp, and Hemi all used the same basic factory torque convertor.

 

[Jack H]

I don't think the TC will affect the vacuum.

Numbers below are probably closer to what you're starting with and heading to.
Factory converters are typically 1800-2500
And (ballpark) you'll be going from 350 to 550 on the torque?

Torque Stall K
350 2500 133.63
550 3134 133.63

350 hp 425 lbs torque now

 

[Katfish]

I would go with what you have, unless as mentioned, the cam puts you into another RPM range

Torque Stall K
425 2500 121.27
550 2844 121.27

On another note, the TC works below the "stall speed", so you don't need to worry about cruising at 1800 RPM in OD with a 3000 converter.