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Great read Lenny. Would you be willing to expand on what you wrote, and share a little more in depth converter theory?

I'll try to keep the questions broken out and simple so they are easy to respond to.

1) You elude to the fact that the one way roller clutch (or sprag, mechanical diode, etc...) is suspect to breakage. You point out that a spragless converter can avoid those problems. The one thing that's not mentioned though is that the downside of a spragless converter.

a) Could you explain or elaborate on the downside of using a spragless converter?
b) What are the typical efficiency losses between a spraged stator, and a spragless.
c) If the efficency is focused on in a spragless converter design, what is given up to do so? (What I mean is that a stator designed to be spragless, is unlikely to be the same design for one with a sprag. How does this effect performence?

2) Can you elaborate a little on why during a shift, the RPM doesn't ever seem to fall back to the stall speed? For example, lets take a converter with a stall speed of 5500. And I mean true stall speed, on a trans brake, not a foot brake. If you shift a 727 from first to second 2.45 ratio, to 1.45 ratio. A typical 6500 RPM shift would drop down to ~3800. Obviously this doesn't happen because the converter stall speed is higher then that. But what's puzzeling is that the RPM doesn't ever seem to fall to 5500 either. It always ends up being slightly higher then that (say 5800~6000). Can you explain why?

3) As racers, we love to calculate things. Unfortunately for converter makers, the only real things we can calculate and measure are efficency and stall speed. Can you explain a little how trading off efficency for other attributes can make a car faster? Specifically, it's my understanding that efficiency and torque multiplication can be traded off. Especially on the shift recovery, the added torque multiplication down track, can be worth more in ET then what is lost with the efficency on the big end.

4) Continuing on efficency. Can you explain some other reasons why it's not the "end all, be all" most racers think it is? My point being that unless the motor is VERY peaky, and falls off at high RPM, the torque transmitted to the wheels isn't as low as one might think with slippage % change.

5) With limited availibility of torque converter graphs, there is one thing that I have always wondered. Does torque multiplication fall off lineraly? Meaning if you have a stall speed of 4000. And a torque multiplication of 2:1. Does that mean that at a 2:1 pump/impeller ratio, that the torque multiplication will be 1.5? Is it an exact linear relationship?


Now some of this is just as I understand it. If I'm wrong, feel free to flat out tell me so.

I was lucky enough to have a fairly in depth conversation with Al Adam last year (who worked on the development of the famous chrysler "J" converter) I'd like to hear your thoughts on some of the questions above, and confim I actually retained some information from my discussion with Al...

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What is the typical range for internal clearance between
impeller/stator/turbine for 8" unit?

I'd like to learn even more.........with pictures.

Torque converters are the only thing in the drivetrain,
I have no control over.

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Hi , If you wouldn't mind, give me a call at the shop or give me a number to reach you as of right I have a back log of approx 3-4 weeks. I build every piece and talk with every customer so time is precious. We are here 12 hrs a day most of the time 7 days a week. You have some great questions that would require a very lengthy post but I would bemore than happy to answer all your questions personally in a much shorter time frame. Look frorward to speaking with you.

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Sent you a PM...

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I personally would like to know the effects of charge flow pressure vs. efficientcy. I've been doing my own research on a buddys dyno on TH400 stuff. This is a very uncharted area for most of the general public and would like to see more info on this subject. Higher HP cars tend to push the oil out of the converters faster then it can fill. I'm sure some transmissions are more sensitive to that since the input shaft designs and oil flow paths are different.
Have you done any testing with various types of oil restrictions internal to the converter ? Hub clearance to stator shaft, increasing/decreasing oil channels in the stator ? Effects of different oil coolers of charge pressure ?
Allan G.

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