Let's discuss STR...
Originally Posted by Martingale
Okay, I'd like to discuss STR and its relation to driveability and acceleration. How does STR effect the "loose" feeling, shift extention, and effeciency at high revs?
As far as efficiency at high revs, that depends on more than simply the numbered rating of the converter. Where efficiency mostly comes into play is with the parts used to attain those numbers. There are two main components that determine stall speed and STR. The stator and the pump. The angle of their blades tell the story of the entire converter and how it will perform. For example, if you take one stator and use a positive angle with the pump, I could end up with a 2800 stall with a 1.8 STR. By changing the blade angle to a neutral direction, I would get a 3400 stall with a 2.0 STR. Now, again using the same stator, if I put a negative blade pump in, I might get a 4100 stall with a 2.4 STR. So, as a general rule, as the STR increases, efficiency will decrease; but it is a lot more involved than that.
Thread Starter
TECH Apprentice
Joined: Jan 2005
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Good info man. It seems like the converters with a higher STR also have a higher stall speed, is this correct? So if someone was looking for good driveability the tighter feeling gained by a high STR might be offset by the higher stall speed? Does anyone make a low stall speed/high STR converter that has good driveability and wont cause a traction nightmare? That's really what I'm looking for...gained acceleration and reducing the "dead spots" but without the car feeling totally loose.
Martingale:
STR has a lot less impact on looseness than stall speed. TQ multiplication drops off fast once a car is rolling and so the gains from a higher STR aren't always as much a SOTP gain as people hope. For example I driven a SY 3500 (1.6 STR) and owned a YTP 4200 (2.5 STR). The YTP's stall speed is 20% higher than the SY and its STR is over 50% higher, yet the SY feels and drives noticably tighter.
High STR + Low Stall Speed = Traction Problems. I had the Yank TT2800 (3.0 STR). It was really tight, but even with factory 3.23 gears, it was hard to launch on street tires. It was a great converter but for a 2.73 gear car.
STR has a lot less impact on looseness than stall speed. TQ multiplication drops off fast once a car is rolling and so the gains from a higher STR aren't always as much a SOTP gain as people hope. For example I driven a SY 3500 (1.6 STR) and owned a YTP 4200 (2.5 STR). The YTP's stall speed is 20% higher than the SY and its STR is over 50% higher, yet the SY feels and drives noticably tighter.
High STR + Low Stall Speed = Traction Problems. I had the Yank TT2800 (3.0 STR). It was really tight, but even with factory 3.23 gears, it was hard to launch on street tires. It was a great converter but for a 2.73 gear car.
Good info and right on. 
