redtan

iTrader: (5)

So I have a different question regarding the choosing a right stall for my needs. The way it's different is that I don't necessarily care for the utmost performance in a straight line and don't necessarily need a stall that matches perfectly with the cam/powerband.

I know that this may see counterintuitive, however my planned use for this car is mostly for road course/autox type driving where all that's really needed is a controlled flash to a certain RPM and not violent ones like big stalls tend to do.

Looking for something to basically keep me at or above a certain RPM, let's say 3000. For example, regardless of the speed or gear that I may be in, I would like the stall to flash to at least 3000rpm to at least keep me somewhat in my powerband and smoothly go from there. I don't want to be stuck at the bottom of 2nd gear (too high for 1st) and only see 2000rpm but I also don't want a huge flash to 4800rpm the instant I touch the throttle as that would not be fun coming out of a corner. The latter being an example of how my previous loose 3600 stall would act on the street. Good for roll racing, not good for controlled exits out of a corner.

Is there anyway to figure what type of stall I would need for such requirements or is that not how they work?

Circle-D_Brian

We have done a couple of road raced converters, and found that your thinking is the same as ours. We prefer a bit larger diameter in a slightly lower 3000 stall range for this type of application.

-Brian

mrvedit

I would also highly recommend a triple disk and a tune to lock up the converter whenever possible. Otherwise the slippage from converter heat will overwhelm any cooler.
Road course racing creates a lot of heat - in a typical 2 minute lap, you might be at high/max throttle for 1 minute, and then repeat for many laps.

01ssreda4

iTrader: (96)

On throttle unlocked driving creates a ton of heat. What you are wanting makes sense on paper but isnt practical for a real world application in most cases. Using a converter as a bandaid for poor gearing just plain wont work, at least not for very long. The only way an auto would work for this is a triple lockup unit as stated above so you have zero slippage and can control heat, but even then it would be a nightmare to make work right during the complexities of a road course, or two have a super tight/efficient converter and always stay in the coupled range with little to no torque multiplication happening to control heat....but at that point you realize that having an auto proves only to be a disadvantage because the very thing that makes it an advantage you have to try to eliminate.

mrvedit

Here is an untested idea for tuning for road coarse racing:
* Set very low upshift speed for all throttle positions
* Set converter lockup for 2nd, 3rd and 4th gears.

My hypothesis is that this would give you close to manual shifting - the trans will always be in the highest gear you allow with the shifter.
Annoying on the street, but good for the road coarse race track.

Circle-D_Brian

All very good pointers here. Seems like a good tuning plan to me.

-Brian

redtan

iTrader: (5)

Well short of changing the gearing inside the transmission or doing a 6 speed 4L80E/6 speed T56 swap I'm kinda stuck with the wide gap between 1st and 2nd gears.

So you guys are saying lock the converter the entire time, like at 3000rpm to redline? I've already tuned the transmission up/downshifts very well but still doesn't allow for much room right around 25-35mph where it's in a tough spot between gears.

01ssreda4

iTrader: (96)

Ive always heard lockup during a shift was a no no but ive never tried it personally. As for the gearing, again I wouldnt look to a higher stall speed to compensate for that dead spot. It creates 3 problems to solve one. Maybe look to something to increase power at that rpm, even something simple like an UD pulley or putting the car on a diet.

redtan

iTrader: (5)

Again, I'm not looking at a higher stall perse...I'm looking for the right stall be it a 2400 unit if that's what it takes to get me flashing to about 3000.

I just know a 3600 is wayyy to much, but also don't want to go back to stock and have it be dead in that area.

mrvedit

No, don't keep the converter locked during shifts - in HPT keep "Transmission -> Auto TCC -> Shift Lock" disabled.
With my proposed tune it would unlock during the shift and then lock back up again.

As Brian suggested, a larger diameter converter with a stall right at the beginning of your engine's power curve will be the best you can do, other than getting a M6.

poorhousenext

I'm going to say this. I don't think I can slip my GM 258mm Pro III 4L80E Torque Converter with the HP/TQ I have. If it did slip I don't think car's MPH would be so high. Course lower ET's might lower my MPH too. I'd say it's STR is on the efficient side also.

360 RWHP/329 TQ. Car it's in has a weight of 3559 lbs with me and 4 gallons of gas in it. It has 3.55 rear gear, and traps in 4th gear that is a 1.18 ratio at 117-120 MPH range and converter is never locked. Trans may play a factor in MPH too, as it's a close ratio 6 sp.

redtan

iTrader: (5)

Yeah I didn't mean to keep the converter locked during shifts. So basically, as soon as it shifts (whether up or down) it should immediately lock?

mrvedit

I don't know how fast the PCM algorithm will lock after a shift; a little delay might help get the engine back over the stall speed.

01ssreda4

iTrader: (96)

A converter clutch is NOT designed for that. It would fail quickly subjected to that continued abuse.

mrvedit

Good point, but let me ask Brian or Chris: Can your triple disk handle this or not?

01ssreda4

iTrader: (96)

Im thinking a triple disc maybe, but again that's got drag racing in mind with a one time lockup going down track. Who knows what repeated locking and unlocking would do to the frictions on it, thus dumping the debris into your trans and prematurely wearing your converter out. Again, very simply, creating 3 problems to solve one......

Circle-D_Brian

I don't think a single disk is going to hang for this type of abuse. In our multi disk we have gone to a heat treated steel clutch plate to eliminate warping issues that an untreated steel would encounter in such a high demand application. Let it eat.

-Brian

redtan

iTrader: (5)

Ok so the triple disk seems to be the consensus, but now I have to go back to this:

What's the point of setting a low upshift speed? Do I want to be going down the straight at 50mph in 4th gear WOT?

That's what I do to try and save MPGs by getting into 4th really quickly at a low speed...never thought that was the case for racing full throttle?

RevGTO

iTrader: (12)

I think the logic must be to in effect disable automatic shifting while on the road course. I imagine one would need to fully manually control the transmission while racing as one would do with a stick.

Another factor to consider is if PWM is eliminated (as should be done with any aftermarket hi-stall converter, and especially in your proposed usage), unlocking during shifts will give a wham/bang/wham effect during unlock/lock.

redtan

iTrader: (5)

I'm not too worried about automatic shifting and/or downshifting. For the most part I plan on tuning the shift tables accordingly so that I can leave it in 3 and it will hold all gears to redline no matter the throttle position and only downshift when it gets to a predetermined speed.

And if I need it, I can use the shifter to control gears with the valve body installed.