Something to keep in mind, there is no “magic” number on where a torque converter should flash/stall at in relation to the engines peak torque or peak horsepower. Each car and combo is different. That is why converter manufactures want SO much information when spec’ing a torque converter. If the engine peak torque and horsepower was all that mattered when building a torque converter, then setting up converters would be easy, more people would do it themselves, and stall speed would much more of a mathematical certainty.
Paul at Turbo Action is awesome to talk to. He’s very informative, he helps educate you, and he is able to offer information like he did for Korie when it comes to camshaft design, where the camshaft should be degreed in at, etc. He also will not give you a set number where a converter will stall at, he gives you a ballpark range, and for a very good reason. One thing Paul never asked me on the phone with the many many many 1hour+ long conversations I have had with him is “what power and torque did this engine make on the dyno?” Why? He knows that Dynos (like flow benches) are not all created equal. They are tools that we use as racers to help give us an edge.
I thoroughly believe in using flow benches when porting heads and engine dynos after assembling an engine. But the numbers are only as good as the equipment being used combined with the operator’s experience and knowledge to make those tools function properly. If Paul only cared about things such as peak torque and peak power, he would likely not be a very successful converter manufacturer. I myself am not a converter expert or “guru” for lack of a better term. But I do understand how they function and why things such as stall speed and efficiency are based on much much more than an engines peak power and torque level. I think as racers and automotive enthusiasts, if we all dug a little deeper into the inner workings of a torque converter, we would understand why things such as stall speed, are not mathematically certain.
Good example, close friend of mine and Pittsburghracer has vast experience with engine assembly, engine dyno, head porting, head flowing, and racing. He built himself a 540 big block back in 2012 and before putting it in the car, put it on a dyno. A dyno that he helped the machine owner build. The engine made peak torque of 740 ft/lbs at 5600 rpm (don’t quote me but it was around 5600, plus or minus 100), and it made peak engine horsepower of 880 at 7200-7300 rpm (again, plus or minus 100). He runs a turbo action converter that stalls at 6600-6800rpm.
On 1/4 mile, he always carries high MPH along with fast ET, and 60’ is always good when car hooks (90%+ of the time it hooks). So he is “flashing” his converter WAY above the peak torque value and the car hauls ***. When I talked to Paul about his torque converter (and my own torque converter) when I dropped the spare off on my way to vacation in 2021, I asked Paul if he advised of a stall change. If any change there was to make, he wanted both of us to increase stall speed! Because we were very happy with the way the converters functioned, and how the cars performed, we ultimately decided to not increase, but leave alone and keep for spares like they were intended to be anyway. I apologize for the long post, but I feel there is too much misconception out there about torque converters and where stall should be at, how a high stall converter will be inefficient, etc.
In a way it’s pretty simple, whatever manufacturer you choose, there will be a converter they build for you that works the best, whether it’s a higher stall than you thought, or a lower stall than you thought. And unless you are running a lockup torque converter, which most of us on here are not, then you will always have slippage of the converter in high gear. There is also no “magic” number for converter slippage that says “when your converter slips x amount, the car will have its best ET and MPH”. There is no magic number because the number doesn’t exist. Every car and combo is different and every car has a converter that may be faster, but not as consistent, and maybe more consistent, but not as fast, etc etc. Please keep all of this in mind when contacting a manufacturer and describing what you want when you have a converter built.
Something I didn’t even get into is whether the converter is using a conventional sprag, mechanical diode, or billet steel spragless insert. That’s a whole other topic of conversation, but depending what the converter has also can affect stall speed, and efficiency. Same goes for an aluminum or steel stator.