Science behind building a converter

[west coast]

Wasn't looking for a 2 hour seminar or give anybody carpal tunnel from typing. Just basics I know there is a big difference between stock/SS, comp style stuff then the super classes and top sportsmen stuff but there seems to be some interesting stuff going on with the top sportsmen like lock up converters. Back to the subject so there is colored charts and graphs they work off as a base line then experience from there takes over. In a performance class like us getting the car to 60ft is key, specially with the weight of some of these cars. So with the dyno sheet ( and all other info like weight and gear ratio of rear end and tranny's first gear, cam, head, intake) in hands of the converter company where are they shooting too for the flash of the converter to happen at peak torque or some percentage above or below it?

[Mark Yacavone]

That's insider information, James. j/k

Actually the charts and graphs I've seen have to do with the GM 245 mm core, which is a step larger than the old Opel standby. There are about 8 different factory impellers (fin angles) plus 4 or 5 stators, so it's kind of a mix and match deal there.
Not so much with the Opel 8".
There's really only a couple of stator designs, so they have to be machined to fine tune the combination. The fin angle starts out basically straight ahead or neutral, so it has to be adjusted within it's workable window.
There are a few more subtle tuning tricks but you're always walking a fine line there.

Seeing a torque converter multiplies torque, it stands to reason you would want to multiply as much as you can. Sometimes that flash point wants to be a little over peak, at it, or a little under, but yes, right around it it.

No dyno sheet , but with a popular combo? Usually no problem, with a large enough data base.
Odd ball or Dime Rocket type combos? That's where a lot of S/SS racing experience helps, but also a s.w.a.g. sometimes.

Gotta give the carpel a rest, but specific questions?

[FireSale]

Just to fill in a bit, we're talk'in 5.0L aka 302 EFI Ford spinning a C4 in a Fox Mustang. K-L/SA. Converters should be generic on a conceptual level, which is what Jim is after here, but sometimes it helps to know the combo.

Jim: Performance Automatic has a downloadable torque converter order sheet that might give you an idea of the info needed to put one together for a given engine combo. I have their foreword shift servo and it's first rate.

Dale

[Chris Hill]

Mark,


Are there any general converter fundamental governing equations?


Folks always talk about flash rpm and lock-up, but what happens to torque multiplication when flash rpm is "adjusted"?


Also, what happens if fluid viscosity changes?

[Mark Yacavone]

Chris ,There are some formulas but they are very complex.I certainly can't understand them but you just might.
I found something that might be easier to comprehend for most here:

http://www.sonnax.com/articles/90-Hi...ction-and-More

On the second part, the best non answer I can give is it might get better or it might get worse.
Generally when you soften one up by machining stators away from factory engineered profiles, you do lose a few % points of torque multiplication . But if it gets you up where there is more torque to multiply at a certain rpm, then you still will have a net gain in ET.

Personally,I haven't seen any big swing in brake stall within what one would call normal drag racing temperature ranges. Once we get to the point where the fluid starts to boil and vaporize, then we will see a loss in 60' times for sure.
I'm assuming you were asking about temperatures, seeing that most folks use one form of 10w ATF or another.
If you're asking about synthenics in converters, I have no experience.
Some else will have to field that one.

[Chris Hill]

Mark,


Thank you! Now trying to wrap my head around the info.


With factory designs, if stall torque ratio (STR) increases, does converter lock-up efficiency increase, decrease, or stay the same?


Do they have converter dynos?


And the guide listed to determine correct converter does not work well for engines that have a wide spread for peak torque rpm and peak hp rpm.

[ss3011]

A good formula to know is K=R/(square root T) R is RPM T is Torque The way this formula works is each converter has a "K" factor, which classifies the converter. This number is usually figured at stall, or no output . So if K is a constant, you can figure the stall speed at various Torques. As long as a converter is not cavitating the K is constant.

example: if the converter has a K of 250 and T = 400 ft lbs then R will = 5000 rpm change the T to 500 ft lbs and R will be 5590 rpm.

K factors are usually figured out by testing on a converter dyno, but if you have a very accurate engine torque curve you can figure it out by doing a WOT stall using a transbrake to figure out the WOT rpm, then plugging the numbers into the above formula.