I see these terms periodically but don't fully understand what it means mechanically and in terms of driving, both DD and on the track. And the stall almost always recommended is around 3600. Another thing I've noticed, is that the smaller the diameter of the torque converter, the high the stall available. May I ask for an explanation?

 

I'll try to explain it but I might even make it harder to understand lol.
Here is a good example of converter flash, Say I have a fairly stock 6.0 with an advertised stall of 3600, When I nail the throttle the rpms will jump until the converter catches the engine (rpms no longer rising) and the converter starts moving the driveline. Say that RPM point is 3600.
Now If I have the converter behind an engine with a supercharger that will make twice the torque down at lower rpms, When you nail throttle it will have more force behind it so the converter won't be able to catch it as soon so the rpms with go higher before the driveline starts turning, That could be 4200rpms or more.

I like to use a rubber band explanation, Picture tying a rubber band to a 1lb weight sitting on a table. Pull at a moderate speed until it no longer stretches and the weight starts to mover... That might be 12", Now take a deep breathe and yank the rubber band as hard as you can, The rubber band will stretch much further but the stored energy will also accelerate it much faster.

http://hughesperformance.com/tc-stall/


EDIT: I will also add this, There is a difference on how many rpms it takes to start the driveline moving when just trying to drive the car normally, A stall that flashes at high rpms will still get the car moving at a much lower rpm making it drivable on the street. The only issue you can run into is to much slippage can cause the transmission to get hot, A good trans cooler is a must.

 

Since you mentioned a 3600,we'll use a Yank SS3600(I have one) for explanation.
It's stall rating is 3600,factory OEM 98-02 f-bods have a 1800 stall. Some stalls are 'tight',some are 'loose'. I consider mine tight,at a standstill,idling,I drop it in gear and the car will want to start to creep forward. A loose convertor has to be given some throttle(not much) to get to move.
Flash is typically considered the stall rating. If I give it high or wide open throttle,it'll jump to about 3600 where a more positive 'engagement' of the convertor occurs. And there I'm in a higher more power part of the powerband compared to if I had to start from 1800. Flash/flashing can/will occur in any gear.
I'll let the stall vendors talk about size versus stall.
Although I did have a Buick with a 'switch pitch' convertor controlled by a switch on the throttle linkage,low and high stall from one convertor.

 

Bottom line? If you're considering buying a converter , buy the best one you can afford.

 

Cory, since I know you are a sponge for information, here is more:
https://ls1tech.com/forums/automatic...str-guide.html

 

I made that mistake... got the top of the line billet circle D converter $$$.. hate it!! It's loose, I wish I would have researched more instead of just spending money.

 

Thank you LLLosingit and FirstYrLS1Z for the information.

Also, thank you mrvedit for that link (written up by LS-ONE_DAY).

It helped clear up some misconceptions. I had thought that stall speed and tight/looseness were sort of the same thing but I see that's a gross oversimplification without considering torque and other factors.

Does the "turbine" fin angle inside the converter determine stall or is that the diameter of the converter, or a combination of the two? As I said in the OP, I've noticed that a smaller diameter equals a higher stall.

Is a 3600 stall generally recommended because that's about where in rpm's most of the engines in cars on this forum hit their powerband?

 

Cory, I think one of the converter sponsors/experts will have to answer your question about internal parts, fin angle, etc. Smaller converters do tend to have a higher stall.

When I asked CircleD for a converter which was as tight as possible on the street, they choose the biggest diameter which came close to my desired 3600 stall speed. So I think that larger diameters, which also hold more fluid, are tighter on the street. Just like with my previous Yank SS3600, I can accelerate briskly to e.g. 60 mph while keeping RPMs under 2500. In contrast my earlier crappy TCI "Super Street Fighter" converter needed 3000 RPM to begin moving the car; it was way too loose on the street.

The STR value refers to torque multiplication which occurs when the engine RPM is significantly above the trans RPM, e.g. from a start with high throttle. While you might think you want the highest STR possible, the higher the max STR, the narrower the RPM band of moderate STR; in contrast a converter with a moderate max STR will tend to have a very wide RPM band, and it is this wide band which makes the converter feel tight on the street. A higher STR converter will tend to be faster at the drag street, and as mentioned, feel looser on the street.
Obviously the quality of the components has a huge effect on all this, but given top quality components, this gives you some idea of the decisions and compromises involved.
While the sponsors cannot exactly calculate the STR of their converters due to the million dollar equipment needed, they know how to build a max STR for max acceleration or a moderate STR for street tightness.

Since capelajc seems unhappy with his CircleD, I hope he will send it back to them for a free/inexpensive modification.

 

There are a few different stall speeds associated with torque converters in racing applications. There is footbrake stall rpm, flash stall rpm, transbrake rpm and transbrake flash stall rpm. During a footbrake condition, using both feet, one on the gas pedal and one on the brake pedal. The vehicle will stall up until the drive tires start to lose traction and spin, the highest rpm before tire spin is the footbrake rpm. You can see your flash stall by hitting the gas pedal from a stopped/idling position. Whatever rpm the motor jumps up to before as the drive wheels get moving is going to be the flash stall rpm. Transbrake rpm has been described as a "true stall speed". This is only attainable with a transbrake equipped transmission. It is the highest stall speed that the converter will see from a launching condition and is achieved by applying both forward and reverse at the same time. When launching a tranbrake equipped car you may notice another "flash" after the release of the brake. That can also be considered part of the "stall speed" measurements.

Here at Circle D Specialties we will spec a converter based on the flash stall speed. So sitting there at idle and mashing the pedal. We can always spec a converter for footbrake rpm or transbrake rpm but most of the stuff you see will be flash stall speed as that is what most customers are looking for.

@capelajc Please contact us about your converter. Our billet Pro Series converters have a free stall change service and warranty associated with them. We will get you what you want and make it right.

 

i have to apologize to Circle D, I should have specified that my comment to the quote meant I should have done more research on what would best suit my driving needs and not just buy the most expensive or what others suggested. They stand behind their product!

Yes, I hope to have mine restalled to a closer to stock feel. My car will never see the track or raced and I would much rather have it back to normal.

 

capelajc, what don't you like about having a high stall as a daily driver? How much higher than stock is it? I had my torque converter set at the stock stall and kind of wish I had bumped it up a touch to where I could feel a slight difference but it wouldn't cause overheating issues (without a cooler) or being rough driving around town.

 

IMO Converter makes or breaks the entire car. I wouldn't have considered a 5.3 turbo swap without a 9.5" lockup unit, I called Yank and asked Dave for his tightest, lowest stall converter which turned out to be 2800. Great for stock engines only making up to around 500~ horsepower (Depends on the dyno of course. If I get 650rwhp on a dynojet I might see 480 of that on a mustang dyno) and still wanting max economy.

 

A little history on my situation. I've owned the car for 17+ years and never driven a car with a stall. I updated my motor H/C/I, LT's, rebuilt my tranny etc all at the same time last year with the only purpose being to update the car to today's HP numbers. A stall was recommended, so of course I go with most expensive...billet 3600...thinking most expensive would just =best.

I do not like the way the car has to rev up to move around town, and when you are off the gas the car sometimes jerks if you are not in a lower gear depending on how fast you are going. Basically it feels like you either have to have your foot buried in the gas or off, there is no more comfortable cruising. I much rather have it back to something that is smoother to drive on the street. My car is never on the track or raced.

 

Do you have 2.73 gears?

Some of your situation sounds like a tuning issue. Converter able to lock in all gears and locking up at to low of a speed. Next time it bucks a bit keep your foot on the gas and very lightly push the break and see if it goes away.

I used to have 3.73's and a Yank ss3600 and I would be surprised if someone knew it had a stall if they were just driving it around. I have a 4000 right now with my H/C setup and will be going to a 4400 this spring.

 

Rear end was gone through and new axles, TA cover added but still stock gears.

Ok that's good to know about tune...would that also eliminate the need to rev it so much to get it to move in light to light driving?

 

No, that's why I was asking what gears you have. With a higher stall it will feel much looser with 2.73's as opposed to 3.23's which is the other gear ration offered in automatics. The higher the gear the tighter a high stall will feel.

As far as the converter tuning.... most, me included, do not have them lock up in any gear except 4th and only above a certain speed. I have mine tuned to lock up in 4th OD only and only above 50 mph

 

Interesting information, thank you very much.

 

IMHO, Stall-Speed divided by rear-end-ratio should be close to 1000 (or less) for even a quality converter to feel tight on the street. So, a 3600 stall with a 3.43 is close enough, as is a 4000 stall with a 3.73 rear.
But your 3600 stall divided by 2.73 is over 1300 which will feel very loose even with a top quality converter.
I suspect you may have asked for "max" acceleration which might have prompted CircleD to select a smaller diameter converter, which will also feel looser.
I don't think any tuning is going to make it feel much different. With a hot cam you often have to raise the lockup speed as a cam'ed engine will surge under 2000 RPM.

While CircleD probably can improve the converter for you, it will cost significant labor/$$$/time to remove and re-install the converter. I would strongly suggest you instead invest in a 3.42 or 3.73 rear end which will both feel much tighter and improve acceleration. All these parts - cam specs, converter stall speed and rear-end-ratio work together and you have only addressed 2 of the 3. Take care of the rear-end-ratio and your car will be completely transformed and put a big smile on your face.

 

Talked the builder this morning after reading some of your replies and he suggested I take it back in to try a different tune first, maybe something geared more towards daily driving...which is what I was always after. He also had me check tag for gear code and it looks like I should have 3:23 GU5.

You guys have been extremely helpful to "me" , hopefully I didn't high jack the OP thread.

 

Glad to share info and opinions with you.
I know Cory was just looking for info ("Need more input") and you therefore didn't hijack anything.