Ep. 5 Torque Converters 101: What Is Stall Speed?

In this weeks episode, we're discussing stall speed and what that means exactly! We hope this video will dispel many myths and confusion surrounding stall speed and torque converter function. Please be sure to subscribe to our channel, like, and share our videos. Enjoy!!
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[PatrickBaptist]

Very good video! Thanks for not having lame music or a bunch of other theatrics, just straight to the education.

[herseem]

This is a great video. Years ago I had a Rover 800 2.0 litre with ZF HP14 4-speed automatic gearbox. They were sold as Sterling in the US and I expect they had the 2.7 litre Honda engine over there. As I was having the engine and gearbox rebuilt I took the opportunity to have a custom-made torque converter. I told the torque converter company that I wanted the lowest stall speed possible. They said they could do it, but it wouldn't work as the engine would stall as soon as it was put in gear. I went away to think about it, and the maths involved, and I concluded that they were wrong, so I asked them to go ahead and build it that way. They supplied it to the mechanic who was putting the gearbox back together, and after having supplied it, someone higher up in the company rang him up and said, "We're sure it isn't going to work, so if you return it now before it's fitted, we'll put it back to normal at no extra cost". Clearly, the discussion about it had filtered up and someone more senior had eventually taken a look at the spec after it had already been despatched. I went away and thought about it again and simulated it in my head, and I concluded that I was simply going outside their normal envelope of experience, and that they were extrapolating linearly outside of their experience instead of in proportion to the cube root, which is indicated by the maths. Plus, I'd reached the point where I had to know if I was right or not. So I told the mechanic to go ahead and fit it.

I've got to say that it was almost perfectly how I expected it to be, in that there was a bit of an extra 'kerthunk' when it went into Drive, and the engine vibrated a little more on tickover when stationary, as the torque converter was pulling harder at tickover, but it didn't even come close to stalling the engine. Driving through traffic was lovely, because a lot of the time I only needed to take my foot off the brake to keep up with slow traffic as it would creep at a much higher speed than normal. To make decent progress I only had to breathe on the accelerator and the first to second gear change was extra silky because then engine was revving so slowly when it happened. Commuting right across London at the time I managed to average 35mpg over a tankful, which is pretty good considering that it was a 2-litre, long and relatively heavy car, driving through one of the heaviest traffic areas of the UK for most of my journey each day. But I was especially delighted that my experiment had worked, and the experienced, qualified professionals were wrong. The downside is that at the traffic lights Grand Prix it was definitely slower, because the torque converter was holding the engine speed down to a lower speed all the way through each gear, but if you use a car for normal commuter driving and not racing, then a lower-stall-speed torque converter is much nicer to drive with.

[savagebolt]

When my dad explained a torque converter to me in 1964, I was amazed. Now almost 60 yrs L8R, I see this vid & I'm still amazed!
Thanks so much for making & posting this.

[francfurian]

That was the best in-depth explanation on torque converters I have ever heard.

Cheers😊

[GRedschoen]

I watched several other videos on stall speed and was nothing but disappointed. All of those people need to come and watch this and get an education from you professor. Fantastic video and 100% convinced me of who I need to go to for parts.

[troyrice]

Let me simplify this for everyone....the front spinny thing uses fluid to make the back spinny thing go around and around. The engine speed required for the front spinny thing to spin the back spinny thing when you mash the accelerator thingy as fast as you can is called the stall speed. I don't know why they call it stall speed because it doesn't stall when its spinning.

[trevorplaysguitar]

Well what a shock to pull up a video done by none other than PETE! Wow that caught me off guard.

[mikef-gidg]

Oh baby, this video packed a punch, I learned a lot, especially that I should call for recommendations even on a mils street combo, I finally get it. Excellent.

[TameToothSGA]

Thank you for getting right to the point here and being actually educational. I know very little about how automatic transmissions work and i want to understand more so i’m gonna binge this whole series

[PewPewFishing]

Explaining driving behavior in relation to stall speed ratings helped me understand what my TC is doing. Great Video.

[charlestackett]

As a student, I appreciate information that I can understand. This video helped me understand stall speed and the factors that influence its variability. Thank you.

[arthurrose]

Once again, excellent, concise with some impeller/stator/turbine design details and stall speed clarification.

[coolbreeze]

I was glad to hear that about the foot brake stall. I don't like power braking at all and don't do it. I've taught my sons it's an embarrassment. If the car won't spin the wheels on it's own free will then build a bigger engine.

[mericafreedomland]

Nice to know Youtube listens to or watches my text 5 hours ago I had this exact discussion with my buddy about stalls and tq converters lol

[dennispope]

Very impressive, a lot of good information. Will be in touch when I upgrade my TH400 to TH200R4.

[peterspengler-hp]

hello gents, you do very informative videos and they are great in helping to understand how all that stuff in the auto and converter works, I recently installed a 80/40 billet drag cam into my 304 V8 with a 4L60e box, the part i don't quite understand is why it wouldn't idol in gear with the standard converter, i ended up having to get a 2500-3000 hi stall converter for it, what had to happen to the converter to so it would idol in gear, never understood that part of the auto box, I look forward to watching more of your videos because I am learning so much about the auto gearbox, again, thank

[elopez]

I watched two of your explanation videos and knew right away to subscribe. Excellent and very helpful!

[countryprepper]

I am getting started on my 1971 Nova build. Just got my 383 stoker built, I was thinking in my mind I need a 2, 500 stall. I wake up this morning and this is the first video on my recommend list. LMAO 😂

[infamousdjnoxzeit]

i really appreciate this video, in short the more you slow down the fluid coupling from happening/ efficiency the higher the stall speed/ the more torque can be output by engine without overriding torque converter, trans, etc. Thank you so much finally understandable. :)

[johnhutsenpillerjr]

Turbo hydramatic 425s had a variable pitch stator. VERY efficient. Shame they quit making them.

Caterpillar hydrostatic transmissions had a unique torque converter design...
Ever seen one ??
Great video Sir.