Now it's a torque converter question

[R-WEST]

Eventually I'll get this figured out!! 

Now I need opinions on a TQ.
I'm sure everyone's tired of seeing the specs, but, here they are again:
'76 F100 Shortbed; 3500 lbs (weighed on 2 different certified scales +/- 25 lbs); .030 over 390; 10/1; Ed. ..69's; port matched to plenum modded Streetmaster; 750 Quickfuel; Comp 282S at 104 c/l; Faron'ized Duraspark with MSD Streetfire; 1-3/4" headers; 2-1/2" dual exhaust; 31" tires; 3.89 (maybe 4.11's, after reading Paulie's response in my 'which cam' thread) gears; C-6 (don't know the ratios, but I'm guessing they're whatever would have come stock in a '76 F100).
Truck will be used for cruising locally, shows, etc..
Vacillating between a 2,500 and 3,000 RPM Hughes.
Thanks,

[jayb]

I think either would work, but if I had to pick with your combination I'd probably go with the 2500 stall converter.

[ScotiaFE]

C6 gear ratios

Stock 2.46 1.46 1.00
Aftermarket gear set 2.72 1.54 1.00 

My experience with a Hughes 10 inch was it never got to the stall that it was rated at.
Mine is rated at 3500 and it probably stalled at just under 3000 behind a modest 428. just saying.

[machoneman]

Seems (almost all the time from many other blogs) a rated convertor from any of the big makers never seems to hit the intended stall speed. Have seen lots of buyers disappointed when this occurs btw. While a lot of factors do enter into actual stall speed, even given real world car/engine data, it seems no one ever gets a convertor that stalls at a higher than expected rpm level!

I still wonder why.

[My427stang]

How do you guys measure it?  Clutch guy here, but with power and load affecting converter stall, I understand that without a transbrake you will generally never get even close to the true stall. 

The next question is, should a footbraker add more converter to compensate for that?

[jayb]

The way it has been explained to me is that there is a "flash stall", which happens when you mat the pedal from low RPM, and "stall", which is where the engine drops down to on the 1-2 or 2-3 shift under full throttle.  If you've got a datalogger you can easily see this; you look at the RPM trace when you mat the pedal and it will climb at a high slope to a certain point, and then start climbing at a lower slope after that.  The point where the slope changes is the flash stall.  Then on the 1-2 shift the RPM will drop to a certain point, and that is the real stall speed.  Its a lot easier to see on a high stall converter, I think; on my cars, especially my Galaxie, on the 1-2 shift the RPM drops to about 6400 and stays at 6400 for a brief period before it starts climbing again.  This is the car catching up to the converter; the gear ratio change wants the engine speed to be lower than 6400, but the converter stall speed holds it up higher until the speed of the car catches up.  Once it catches up, the engine speed increases again.

On my cars the flash stall speed is about 500 RPM lower than the real stall speed, and I think this is due to the fact that on the shift the engine is already well up into the power band and the converter is loaded harder.

[Joe-JDC]

Actual torque also affects the rpm at stall.  Most folks overestimate their torque and the rpm where it is most beneficial for launch.  The same converter will stall higher with more torque in another engine with more torque.  I have a JPT C-4 with C-6 adapter and use a converter that stalls at 4500 with a 351W, but would stall at 5400 with 427 MR in my 69 Mach I.  The same converter.  Joe-JDC.

[machoneman]

True that with a different engine or combo the stall will change. Amazed that many a Stock class and even SS auto racer has 1/2 dozen converters in the hauler to fine tune the same engine for different tracks.