im kind of confused.
1). would a converter with a higher stall-torque-ratio (2.5) have a higher efficiency than one with a lower STR (2.0) or the other way around?

2). which one would feel tighter when just driving around?

3). what exactly does stall-torque-ratio mean?

i've looked around some and i cant find a place to answer these questions so i though this would be a good place to ask

 

It really depends on design. A well designed high STR can be as efficent as a low STR converter. A lot of cheap converters for older cars were not efficent when they had high STR.

 

All else being equal a converter with a lower STR would tend to be more efficent. Especially mid range to top end.

A converter with a higher STR will normally feel tighter.

STR means how many times the converter multiplies your engines torque. A converter with a 2.0 STR would multiply your engines torque 2X for example.

 

so it will multiply your engine torque by the same ammount at every rpm? what about after your past the stall speed? a less efficient converter will have more driveline loss correct? and what would you guys reccomend for a street/strip car?

 

if your motor makes 300 ft lbs of tq at the motor, it "creates" for a flash 2.x times at the tranny (that is why you need a tranny cooler). ofcourse the is multiplying before it gets through the drivetran, but that is why big stall convertor cars make so much tq when it is flashed on the dyno. my yank st-4000 2.6 str is very efficient as all of the yanks. the PI convertors are slightly less, but you wont notice that much compared to the yank. i have traped at over 116 mph at 3500 lbs on a cam only car.

 

also go to yank's website, they have a lot of info you are asking about. and all things equal, a higher str will be a bit tigher, but ofcourse if you pick a 4400 rpm convertor, it is gonna be loose also more rear end gearing and it feels tighter.

 

gator. do you have a link to yanks site?
edit: it doesnt seem to be "yank.com"

 

www.converter.cc

 

STR occurs at the stall speed just as the output shaft begins to rotate. Once the output shaft starts to rotate (i.e. the car is moving) the amount of torque multiplication declines.

FWIW, Yank's most effecient converter was the TT2800 with a 3.0 STR, beating the famous SY 3500 in efficency. The TT2800 was a great design. The low STR of the SY made for easier launches and its longer shift extension and high efficency made it a killer street converter and more popular than the TT2800, which was ideal for mild 2.73 cars.

 

The big difference in a high vs.low STR converter isn't the efficiency.
It's how fast the torque multiplication drops off.The lower STR converters tend to
drop off slower, giving you greater torque multiplication at higher rpms.
Take a look at the dyno graphs on Yank's website and you'll see what I mean.
A TT2800 with a 3.0 STR has high efficiency but the torque curve drops off much
faster than a SY3500.
That's why a SY3500 is tough to beat from a roll; it maintains its multiplication
longer.

 

Stall is a much bigger factor in shift extension than the STR. That accounts for most, if not all, of the difference between the TT2800 and the SY 3500. Add the 2.7 STR YTP 4400 into the analysis and you'll see that.

For example compare the SY 3500 and the ST 3500. Same stall but different STR. The shift extension is virtually identical.

There are no absolutes. what you get from a converter is a function of many factors.