DREAMZ28

iTrader: (1)

I've searched, and every answer seems to be different. Some say low str is going to make the converter looser, some say a high str is going to make it looser, and some say str plays no role in driveability. So basically what I want to know is what decides how a converter acts around town, and if str is a deciding factor, what is the truth behind it?

Kurt D

iTrader: (2)

Way back, 10+ years ago, when I had a stalled auto and Yank and PI where your only real options, I've always read the higher the STRs might feel tighter but where less efficient. In real life I don't think many made it a habit of swapping verters back to back to see but in general the ones who had the opportunity to drive cars back to back with the same brand of converter supported that theory. It was one of the reasons I went with a Yank ST3500 instead of the SY3500, the higher STR. I didn't have the opportunity to try a SY to give a comparison but the ST was perfect on the street.

Also drivability is an opinion, what's acceptable, or excellent to me may be horrible to you. Comparing STR across brands, even models, is also futile as the design may effect drivability more so than simply STR. The ST and SY I mentioned above where built the same, with same stall, and the difference was the STR, I don't know if anyone still offers similar options.

jimmyblue

iTrader: (11)

I've never felt I have a good idea what other people
mean by "tight" and "loose". But here goes....

My low STR Fuddle, I spec'd with the idea of getting
as good a low speed coupling as my old 3000 TCI.
The result is something I'd call "stretchy" - there is
indeed some decent low-pedal coupling, but RPM
swings wider when you open the pedal. And doing
so, you still have torque multiplication happining out
past 5000RPM.

A high STR, same RPM converter is going to not
couple as much torque at the low end, you might
need another 500RPM or so to get moving at any
kind of acceleration, and you will have huge torque
mult in the midrange but it will fade to 1:1 earlier,
possibly feeling like it "lays over" if your motor
torque is also fading (as a stock motor does).

My thinking was, I wanted more efficiency and for
the torque converter to deliver more even multiplication
over a wider RPM range, and less of it at peak since
there is no prayer of hooking it up on street rubber,
lowered anyway.

I think the low STR is more pleasant and controllable
to drive - the only thing I would want a high STR for,
is a track car that is set up to make use of huge
torque off the line, lift the fronts and plant the rears
while the jerk-torque reaction is still in play. You need
some rear wheel torque to do that. But you also need
the back-torque of stuck (or real sticky) tires or it's
all for nothing.

A high STR will act real impressive as far as making noise
and wheel spin, and that tends to move product. But
it may not be what moves you best, given the road,
rubber and mission you're on.

mrvedit

Jimmy, thank you for yet another good explanation about converters and STR.\
Correct me if I am wrong, but you seem to be saying that a converter with a low STR has more of a wider "stall range" rather than a very specific stall speed (i.e a narrow stall range).

RevGTO

iTrader: (12)

Higher STR makes the car more responsive when pulling away from a stop, for the same reason it delivers a bigger hit when launching. There's a greater delivery of torque to the rear wheels, and thus less feeling of slippage (looseness) - that's why people often report that their Yank SS3600 "drives like stock." It's a high STR converter.

Yep, Ted, you read Jimmy correctly about a lower STR converter having a "wider stall range."

LS-ONE_DAY

https://ls1tech.com/forums/automatic...str-guide.html

DREAMZ28

iTrader: (1)

Ok so I'm getting mixed answers again lol. Well I already have a converter, it's a PTC 4000 rpm converter, he said between 1.5-2.0 STR. Compared to Yanks converters, that STR is allot lower, and Yanks converters are pretty civilized.

sabersaw30

iTrader: (10)

I like the lower str for street driving got a fti 3600 1.78 str 60ft in the 1.60 range.And you can keep your top end pull on the street. Higher str you will loose some top end pull.