hog

Anytime the torque converter is turning faster than the trans inputshaft the TC is multiplying torque. Locking the TC eliminates this.
I understand where you are coming from, but in your explanation, it seems as though you think that if a TC has a stall speed or coupling speed is fixed, and it is, but if teh vehicle is moving the the indicated this coupling rpm will increase based on the vehicles speed.

When launching off the foot brake, lets assume the trucks brakes can hold the engines output and not allow the tires to spin(hypothetically). Lets say the truck is running a 4000 rpm stall speed, and in gear, at WOT the resultant rpm is 4000rpm. OK at this point vehicle speed is zero so the TC body is spinning at 4000rpm and the input shaft of the trans is NOT spinning.
So no we launch, engine rpms increases as the brakes no longer hold the tires stationary. Engine rpm increases to say 7500rpm, what is the input shaft of the trans doing?
Lets say the input shaft is spinning at 3500rpm(although its probably spinning a bit faster).
Now its time to upshaft, lets say that engine rpm, therefore torque converter case, is now spinning at 5000rpm, because of the TC's stall speed, the input shaft of the trans is now spinning at around 1000rpm, and because we are now in 2nd gear, the output shaft is spinning faster than it has during this pass.
My point here is that TC stall rpm, is really the measure of the difference in rpm of the TC case and the trans input shaft at WOT. As engine rpm increases, the transmissions input shaft speed will increase in a roughly proportional rate. At no point during upshifting at WOT will the engine rpm ever be BELOW the stall rpm of the TC. So long as the engine is at WOT the differential in rpm between the engine and transmission input shaft will ROUGHLY be the same. As engine rpm increases, input shaft rpm increases, an upshift causes the input shaft rpm to decrease, which in turn causes the engine rpm to decrease.(shift extension)

This is why all else equal when doing roll ons, an auto vehicie will out accelerate a manual trans equipped vehicle. This isnt to say that clutches cant multuply torque, they can, but only when they are slipping. Think of a 2 stroke dirtbike. If it is bogging a bit in a turn, a quick blip of the clutch allows the engine back into powerband and away you go.

I do 100% agree that locking or not locking the TCC is dependent on the combination. Much power/torque is needed to take advantage of a locked TCC in drag racing.

For max acceleration, you want a TC to stall or engage at the same rpm at which the engines peak torque is attained. Often this is undesireable for street use, esp. in heavier vehicles like trucks.

Biggest point here is that any time there is a difference between the engine rpm AND the input shaft of the trans, torque multiplication is occuring and you are "riding on the converter" thats how torque converters work.

So far as datalogging, in order to see which approach is better, simply log the speed sensor on the output shaft of the trans. Whichever method causes the speed sensors pulsecount to increase FASTER is causing the truck to accelerate faster.

The more torque you feed a TC the higher the stall speed becomes. This is why we can pull away from a stoplight at 1500rpm under light throttle(low torque input), but at the same time, that same combo can stall to 4000-5000rpm at WOT(high torque input) at the dragstrip on the transbrake.
This why small cube engines NEED higher stall TC's, they simply dont feed the torque like a larger engine does.
A TC that stalls at 1800 rpm behind a 4.3, stalls to around 2800rpm behind a Vortec 350. This is why my DCLF code L35 TC works behind my 350, more torque, more stall speed. Which allows the engine into its torque/powerband faster.
Centrifugal supercharger with a stock TC can be a slug out of the hole, install a TC with a high stall speed, that same vehicle can be an animal.

TC's are a tough subject to talk about, esp. via a keyboard. TC's are also one of the most overlooked parts of the performance equation.

peace
Hog

LIL SS

iTrader: (9)

Hog,

I think you and I are on the same page.

A lot can affect the flash RPM of a converter on the start line. Same exact combo except I lost 300lbs, flash rpm went down (less load or weight to push). Changed gear ratio from 3.73 to 4.56, again flash speed went down as the gear is effectively acting as less/more leverage for the same weight.

You are right that a lot of people dont think about that.

Another thing that people don't think about, the flash speed vs shift extensions and what happens to the coupling properties. 1-2 shift puts less load in the engine than 2-3 because of the gearing AND aero at speed also puts more load in things.

The lock up points I provided above worked for my combo. Each will have to find the sweet spot for their combo.

hog

Good points about gearing affecting flash rpm.

I didnt realize that so many guy were locking TCC's duing a pass. I always wondered why guys were insisting on going with 3 or 5 disc TC's when they werent locking at the track. Ive heard the good muli disk TC's feel like another shift. Even with a single clutch aftermarket TC like a Vigilante, the clutch surface area is at least 2-3 times the area of the stock TC's. On my low power setup, not locking in 3rd was worth a tenth. Using teh stock trans tune would lock teh TCC at 75mph which was right after my 2-3 upshift and it KILLED acceleration momentum. Before I had PCM tuning ability, I used to hold the brake ever so slightly right after the 2-3 upshift to keep the TCC from locking. Always got questioned why I would brake so early. lol

peace
Hog