STR behavior 'under' rated stall speeds.
02-18-2005, 10:44 AM
#1
TECH Addict
Thread Starter
Join Date: Oct 2003
Location: Central, MA
Posts: 2,618
Likes: 0
Received 0 Likes
on
0 Posts
STR behavior 'under' rated stall speeds.
I got a weird one.
If I understand STR correctly, the STR rating is only "true" when the input shaft of the tranny is stationary, and the converter is at it's rated stall speed... correct?
The STR 'fades out' or 'trails off', as the input shaft of the tranny begins to turn. That happens when the vehicle launches.
What happens with STR during normal daily driving below the rated stall speed?
Say I pull away from a stop with my stock 1,800rpm, 1.9 STR converter. I see 1,800rpm on the tach. Say I'm putting down 200ft/lbs and I require 25% throttle to keep up with the flow of traffic. I don't really care what the stall speed or STR is doing at this point.
Now say I have a relatively tight aftermarket stall in there (2,400-2,600rpm) with a 2.1 STR. Say I pull away from the stop at the same 1,800rpm. Will that 2.1STR help me get the same 200ft/lbs to the ground at a different amount of throttle? (less?) ... because it's multiplying engine torque better than the stock converter did?
Another easier example: I need 2,500rpm to get up this long hill - which converter will require less throttle to do so? Stock or the 3000rpm stall with the nice STR?
...Or is the larger STR of the aftermarket stall decreased so much by the turning input shaft of the tranny that the difference is really negligible at best? I'm not sure how much the STR is decreased...
At what number does STR begin at? 0 at 0-rpm? 1.0 at about 500-rpm -- the slowest speed it's possible to get the truck rolling?
I'm trying to piece together a spreadsheet/chart of different converters to visualize how STR effects certain RPM ranges. Looks great so far, just don't know if my numbers are legit.
If I understand STR correctly, the STR rating is only "true" when the input shaft of the tranny is stationary, and the converter is at it's rated stall speed... correct?
The STR 'fades out' or 'trails off', as the input shaft of the tranny begins to turn. That happens when the vehicle launches.
What happens with STR during normal daily driving below the rated stall speed?
Say I pull away from a stop with my stock 1,800rpm, 1.9 STR converter. I see 1,800rpm on the tach. Say I'm putting down 200ft/lbs and I require 25% throttle to keep up with the flow of traffic. I don't really care what the stall speed or STR is doing at this point.
Now say I have a relatively tight aftermarket stall in there (2,400-2,600rpm) with a 2.1 STR. Say I pull away from the stop at the same 1,800rpm. Will that 2.1STR help me get the same 200ft/lbs to the ground at a different amount of throttle? (less?) ... because it's multiplying engine torque better than the stock converter did?
Another easier example: I need 2,500rpm to get up this long hill - which converter will require less throttle to do so? Stock or the 3000rpm stall with the nice STR?
...Or is the larger STR of the aftermarket stall decreased so much by the turning input shaft of the tranny that the difference is really negligible at best? I'm not sure how much the STR is decreased...
At what number does STR begin at? 0 at 0-rpm? 1.0 at about 500-rpm -- the slowest speed it's possible to get the truck rolling?
I'm trying to piece together a spreadsheet/chart of different converters to visualize how STR effects certain RPM ranges. Looks great so far, just don't know if my numbers are legit.
02-18-2005, 10:57 AM
#2
TECH Addict
iTrader: (2)
Join Date: Feb 2004
Location: Tampa, Fl
Posts: 2,784
Likes: 0
Received 0 Likes
on
0 Posts
You know quite a bit more than I, but from my experience the aftermarket converter requires more throttle period. It doesnt lock up until a higher rpm. Before that it isnt fully engaged.
In my experience the stock stoll requires less throttle in situations like those you are describing.
In my experience the stock stoll requires less throttle in situations like those you are describing.
02-18-2005, 12:21 PM
#3
TECH Fanatic
iTrader: (5)
Join Date: Sep 2003
Location: Mobile, AL
Posts: 1,074
Likes: 0
Received 0 Likes
on
0 Posts
I agree with greentahoe.. It takes considerably more throttle to get my truck moving with the stall under normal driving conditions.. but if im in overdrive cruising up a hill its the same throttle position because the converter is locked... now if your starting off going up a hill then with an aftermarket stall its going to take more throttle..
02-18-2005, 12:40 PM
#4
TECH Addict
Thread Starter
Join Date: Oct 2003
Location: Central, MA
Posts: 2,618
Likes: 0
Received 0 Likes
on
0 Posts
Thanks guys...
That little chart I have is sort of reflecting what you're saying...
It seems like the STR only factors into things at a very hard launch. I was hoping to hear it had enough of an effect at part throttle to actually provide power over stock at the same throttle and same RPM. The more I dwell on it, the more I realize it wouldn't really be possible.
Excel chart.
That little chart I have is sort of reflecting what you're saying...
It seems like the STR only factors into things at a very hard launch. I was hoping to hear it had enough of an effect at part throttle to actually provide power over stock at the same throttle and same RPM. The more I dwell on it, the more I realize it wouldn't really be possible.
Excel chart.
02-19-2005, 05:58 PM
#5
TECH Apprentice
Join Date: Mar 2004
Location: Ontario, Canada
Posts: 361
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by marc_w
It seems like the STR only factors into things at a very hard launch. I was hoping to hear it had enough of an effect at part throttle to actually provide power over stock at the same throttle and same RPM. The more I dwell on it, the more I realize it wouldn't really be possible.
url]
url]
02-19-2005, 07:44 PM
#6
If you think about it, if you had a 1.9 STR ratio, then you would have 1.9 multiply in torque just in the lower RPMs. If you view a dyno graph, if STR multiplied across the whole RPM range, comparing auto and manual tranny cars on the dyno would be drastically different in ratings and on the track, the automatics would have lower E.Ts.
This is the way I've thought of it, am I right?
Philip S.
This is the way I've thought of it, am I right?
Philip S.
02-24-2005, 11:53 AM
#7
STR will act diff. in converters of diff. companies and even at the same stall ratings, so tring to make a graph will be only work on one style at a time!
If you have the converter profile from a Dyno test on a converter dyno, as an in car test is not controlled, you can only estimate the STR on that graph
Converters that have a long shift extention it will increase torque for a longer time but only in the .2 to .3 % range at the drop back RPM and go to 0 at aprox 200-300 rpm past the shift extention point and depending on the converter design you can also go to a negative on the STR in the upper RPM range!
If you need some dyno info to help
call me
Mike 479 632 6355
Also the higher you brake stall the converter the lower the STR will be, (there is a sweet spot) on the starting line more torque from the engine will come to play to offset the slight decrese in the STR
If you have the converter profile from a Dyno test on a converter dyno, as an in car test is not controlled, you can only estimate the STR on that graph
Converters that have a long shift extention it will increase torque for a longer time but only in the .2 to .3 % range at the drop back RPM and go to 0 at aprox 200-300 rpm past the shift extention point and depending on the converter design you can also go to a negative on the STR in the upper RPM range!
If you need some dyno info to help
call me
Mike 479 632 6355
Also the higher you brake stall the converter the lower the STR will be, (there is a sweet spot) on the starting line more torque from the engine will come to play to offset the slight decrese in the STR
Thread
Thread Starter
Forum
Replies
Last Post
