How does the stator effect stall, str, tightness, and efficiency?
Thread Starter
On The Tree
Joined: Jan 2012
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From: Elswhere
The title says it all. The reason I ask is to understand what would happen if you took a proven converter, added a variable pitch stator to it, then made it fully controllable (continuously variable). The stator would have to, at some position, resemble the original stator of the converter (to give results similar to its original advertised claims). To what degree does the stator effect stall speed? I've always thought that the impeller/turbine were more important when determining stall speed. Also, how would the str/stall speed correspond? say you take the SY3500 (the best converter I've never had) and adjust the str to 2.5. What happens to stall speed? (Up, down, or hardly effected.) Also, could you even go from a 1.63 str to 2.5, or would the effects of the variable pitch stator only allow say a 2.07 str? I understand that to a degree, higher str = better dd converter. Lastly, efficiency. Does it always go down as str goes up? why does a 2.5 str have better low/midrange efficiency than a 1.63, but worse topend efficiency? And if you did give the sy3500 a variable pitch stator, and angled it to a 2.5 str , would it be anything like an ss3600, or would the less than ideal stator shape have such a negative effect on flow that either (a) you'd just want to leave it alone for light throttle operation, or (b) a smaller angle, yielding only a 2.1 str, would flow efficiently enough that low throttle slip would be reduced (though still not as much as the ss3600).
This is mainly a sponsor question. Unless there's some ordinary guy roaming the automatic transmission forums that has an inconceivably vast amount of knowledge concerning the way converters function.
This is mainly a sponsor question. Unless there's some ordinary guy roaming the automatic transmission forums that has an inconceivably vast amount of knowledge concerning the way converters function.
I don't have much understanding, but aside from whatever
benefits may accrue there's the big problem of how to do
any sort of linear / proportional control of stator blade angle
inside a spinning wet shell. Adding a variable pitch stator
needs you to overcome that problem if you intend to vary
it.
The ST400 was just a valve controlled pressure port with
two (on, off) positions. So in the spinning mass you have hinges,
levers and some sort of piston & spring I suppose to move
it all. Compared to a simple fixed, brazed vane. That accounts
for the crazy weight, I expect.
Now if you want detailed control, that's probably a proportional
pressure through the feed, meaning the valve has to be
chopped and that duty cycle mapped or feedback-controlled
to get whatever desired result. But who's to say that the
intermediate points, beside the hard-stop ones, have any
desirable behavior? And can the stator vane geometry (a
key design decision, I gather) be optimized at more than
one point in the arc?
It's an interesting thought experiment, but I expect it's
got good reasons why it's not done (people keep trying
on CVTs, too, though...).
I have been told that for a given stall speed, STR vs
efficiency is a pretty straight trade. The SY3500 was a
very low STR and very high efficiency. I tried to hit the
same goals but with slightly higher STR (2.0). I don't
think I see the same efficiency but it's hard to say what
true efficiency is when torque multiplication is happening.
benefits may accrue there's the big problem of how to do
any sort of linear / proportional control of stator blade angle
inside a spinning wet shell. Adding a variable pitch stator
needs you to overcome that problem if you intend to vary
it.
The ST400 was just a valve controlled pressure port with
two (on, off) positions. So in the spinning mass you have hinges,
levers and some sort of piston & spring I suppose to move
it all. Compared to a simple fixed, brazed vane. That accounts
for the crazy weight, I expect.
Now if you want detailed control, that's probably a proportional
pressure through the feed, meaning the valve has to be
chopped and that duty cycle mapped or feedback-controlled
to get whatever desired result. But who's to say that the
intermediate points, beside the hard-stop ones, have any
desirable behavior? And can the stator vane geometry (a
key design decision, I gather) be optimized at more than
one point in the arc?
It's an interesting thought experiment, but I expect it's
got good reasons why it's not done (people keep trying
on CVTs, too, though...).
I have been told that for a given stall speed, STR vs
efficiency is a pretty straight trade. The SY3500 was a
very low STR and very high efficiency. I tried to hit the
same goals but with slightly higher STR (2.0). I don't
think I see the same efficiency but it's hard to say what
true efficiency is when torque multiplication is happening.
TECH Regular
Joined: Feb 2004
Posts: 439
Likes: 1
From: burbank ca
stators are torque multiplers. Meaning they work best when your car is stopped. Cut ones increase the stall but drop the torque output. No free lunch"no matter what bama says" but if the stall goes up to where your motor gets happy it's all good. The problem is those tc's act lazy. lf you bend the impeller fins negitive and leave the stator uncut it acts better from a stop but doesn't couple well on the big end. That is why when you buy a tc give the builder as much imfo as you can.
Thread Starter
On The Tree
Joined: Jan 2012
Posts: 158
Likes: 0
From: Elswhere
So... you mean as stall speed increases, str decreases? Inversely, as stall decreases, str would increase, which is exactly the results I'm looking for. However, from the reading I've done, it seems str increases with stall. So considering a 1.63 str has questionable manners as is, dropping stall to 2500 would result in an even lower str = even looser response until near 2500 rpm. Now I just need to know how much str drops with stall speed (if it does indeed drop, rather than increase). If the decrease in stall speed drops the str too far, the manners will be no better than the original converter. As a matter of fact, it might be better to increase stall to 4300 with a 2.5 or greater str. Variable pitch isn't a new idea, but it seems the technicalities of it were poorly documented. If the stall can be lowered to 2500 while only lowering str to 1.4 or 1.3, converter manners should pick up nicely. (stock ls1 f-body is 1700/1.8)
And one last question... I've heard some say that str is far less important for manners than stall speed. Is the ss3600 significantly different than the sy3500 in design, because from what most people say, the ss3600 is near stock under light throttle, wheras most comments on the sy3500 only recommend it for pure road racing, and that light throttle is comarable to driving through mud, and that you need to give it more gas. If str has such a small effect, what's with the large gap in drivability? Anyone gone from a sy3500 to a ss3600 and have input?
And one last question... I've heard some say that str is far less important for manners than stall speed. Is the ss3600 significantly different than the sy3500 in design, because from what most people say, the ss3600 is near stock under light throttle, wheras most comments on the sy3500 only recommend it for pure road racing, and that light throttle is comarable to driving through mud, and that you need to give it more gas. If str has such a small effect, what's with the large gap in drivability? Anyone gone from a sy3500 to a ss3600 and have input?
Last edited by Mr. Sir; Feb 3, 2012 at 10:08 PM.
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From: Schiller Park, ILL Member: #317
And one last question... I've heard some say that str is far less important for manners than stall speed. Is the ss3600 significantly different than the sy3500 in design, because from what most people say, the ss3600 is near stock under light throttle, wheras most comments on the sy3500 only recommend it for pure road racing, and that light throttle is comarable to driving through mud, and that you need to give it more gas. If str has such a small effect, what's with the large gap in drivability? Anyone gone from a sy3500 to a ss3600 and have input?
Like I said in the other thread, the SY is not the ideal drag racing converter because of the low STR, but it's not poor with driveability at all. I very much enjoyed driving with it on the street. Under normal acceleration, the SY really wasn't much different than any other TC of similar stall rating.
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