Stall STR and High End Effeciency.
Apr 11, 2005 | 12:06 PM
#1
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Stall STR and High End Effeciency.
I understand the higher the str on the stall, the harder it will hit and cause traction problems without sticky tires. Is there a relationship on STR and high end pulls.
I have seen several people install stalls and get a better ET but loose mph. To my understanding this stall lacks top end effeciency. Someone please correct if I am wrong.
Really what I am trying to get at is what STR would optimal for highway pulls yet maintaining good street manners(not roasting your tires at .25 throttle) for a 2800-3200 stall.
I have seen several people install stalls and get a better ET but loose mph. To my understanding this stall lacks top end effeciency. Someone please correct if I am wrong.
Really what I am trying to get at is what STR would optimal for highway pulls yet maintaining good street manners(not roasting your tires at .25 throttle) for a 2800-3200 stall.
Apr 11, 2005 | 12:54 PM
#2
Thats a good question Tib. One that I would kinda like to hear the answer on myself. I actually am looking for the other end of the spectrum though, since I installed my cam, I feel I have to give it a little more gas to really get going down low, this is mainly on normal-part throttle takeoffs. Hughes performance, which is the converter that I am using, seemed to know nothing about STR, so I assume that this 2500 converter is using an STR close to stock. Bytheway, anybody know what the stock converters STR is? Not to hijack the thread Tib, but I think this might be beneficial to your questions.
Apr 11, 2005 | 02:03 PM
#3
That is the general rule of thumb. The higher the str, the looser it will feel under stall rpm and the less effecient it will be on the top end but the better it will get you out of the hole. Since I had my TT3000 tweeked a little it stalls about 3200 and has probablly around a 2.28. It does really well on the top end IMO. STR on a stock truck converter is 1.9 if I remember correctly.
Apr 11, 2005 | 03:05 PM
#4
I knew that the stock converter for f-bods had a 1.9 STR, just wasn't sure if it was the same for trucks. Will a tighter converter kinda cause it to feel like it is surging down low though? Mine does this ever so slightly right after I release the breaks since the cam install. Plus I need to lower my RPM idle just a hair.
Apr 11, 2005 | 03:11 PM
#5
Good read...
Yank:
Yank:
Stall Torque Ratio is one of the most misunderstood aspects of torque converter construction. Our competitors often call stall torque ratio: torque multiplier. The stall torque ratio is the amount of engine torque that the torque converter can multiply at a particular rpm level. By definition, stall torque ratio is when the turbine is at 0 RPMs and the converter is at maximum designed stall. This will produce a positive push on the turbine to increase the torque to the input shaft of the transmission, multiplied by the designed stall torque ratio of the torque converter. For example, a stall torque ratio of 2.0 would multiply 200 lb. ft. of engine torque to 400 lb. ft. of torque at the transmission input-shaft.
The misconception of stall torque ratio is that more must be better. This is not always the case. High stall torque ratio applications, typically are for industrial equipment or engines with limited low rpm engine torque. With high stall toque ratio converters, there are important trade-offs. What you take at one end you give up on the other. Typically, a torque converter with a very high stall torque ratio, such as 2.0-2.5, will be much less efficient above its rated stall speed. There is a sacrifice in higher rpm efficiency to achieve high stall torque ratios. That lower efficiency translates into less horsepower transmitted to the tires over an RPM range.
The problem with a high stall torque ratio converter is that it is only high while the car is not moving. Maximum stall torque ratio occurs at wide open throttle with no rotation of the transmission input shaft. As the input shaft starts to rotate with vehicle forward movement, the stall torque ratio will become non-existent much sooner than a converter of the same stall, with a lower stall torque ratio. A converter with a stall torque ratio of 2.2 for example, would display that at the starting line, but it would drop off much sooner than a converter with a lower stall torque ratio.
For example: A competitor's converter with a claimed stall torque ratio of 2.5 (red graph line) would typically have an efficiency of around 90% at high RPMs (5,000 plus). That means 300 flywheel horsepower would translate to 270 horsepower at the transmission input-shaft. A Super Yank Converter with a stall torque ratio of 1.6 (green graph line) has efficiency in the 97% range. That means a 300 horsepower engine would transmit 291 horsepower to the transmission input-shaft: A gain of 21 horsepower! For an LS-1 customer dyno sheet showing 97% efficiency press here.
As you can see, the converter with the lower stall torque ratio will multiply torque for a longer period of time than the converter with a higher stall torque ratio. As most of you know, most racing occurs above 3,000 RPMs. That's why the lower stall torque ratio often wins the race:
*Lower stall torque ratio is gentler on the tires at the initial launch, but it will pull harder for the remaining 1,305 ft. of the 1/4 mile. Less races will be lost at the starting line from excessive wheelspin.
Lower stall torque ratio will be more efficient and transmit more torque and horsepower to the tires. This translates into lower ETs and higher trap speeds!
The misconception of stall torque ratio is that more must be better. This is not always the case. High stall torque ratio applications, typically are for industrial equipment or engines with limited low rpm engine torque. With high stall toque ratio converters, there are important trade-offs. What you take at one end you give up on the other. Typically, a torque converter with a very high stall torque ratio, such as 2.0-2.5, will be much less efficient above its rated stall speed. There is a sacrifice in higher rpm efficiency to achieve high stall torque ratios. That lower efficiency translates into less horsepower transmitted to the tires over an RPM range.
The problem with a high stall torque ratio converter is that it is only high while the car is not moving. Maximum stall torque ratio occurs at wide open throttle with no rotation of the transmission input shaft. As the input shaft starts to rotate with vehicle forward movement, the stall torque ratio will become non-existent much sooner than a converter of the same stall, with a lower stall torque ratio. A converter with a stall torque ratio of 2.2 for example, would display that at the starting line, but it would drop off much sooner than a converter with a lower stall torque ratio.
For example: A competitor's converter with a claimed stall torque ratio of 2.5 (red graph line) would typically have an efficiency of around 90% at high RPMs (5,000 plus). That means 300 flywheel horsepower would translate to 270 horsepower at the transmission input-shaft. A Super Yank Converter with a stall torque ratio of 1.6 (green graph line) has efficiency in the 97% range. That means a 300 horsepower engine would transmit 291 horsepower to the transmission input-shaft: A gain of 21 horsepower! For an LS-1 customer dyno sheet showing 97% efficiency press here.
As you can see, the converter with the lower stall torque ratio will multiply torque for a longer period of time than the converter with a higher stall torque ratio. As most of you know, most racing occurs above 3,000 RPMs. That's why the lower stall torque ratio often wins the race:
*Lower stall torque ratio is gentler on the tires at the initial launch, but it will pull harder for the remaining 1,305 ft. of the 1/4 mile. Less races will be lost at the starting line from excessive wheelspin.
Lower stall torque ratio will be more efficient and transmit more torque and horsepower to the tires. This translates into lower ETs and higher trap speeds!
Apr 11, 2005 | 03:42 PM
#6
A good example of this is my current set-up. I run a fairly loose 3600 stall 2.5 STR PI Vigilante converter. With my RWHP being 425+ my 109 trap speed is a bit low. The inefficiencies are pretty obvious.
With regards to the above quote. This illustrates a NON lockup converter issue. With such modifications available through Precision Industries as a triple clutch plate lock-up assembly engaging the lock up earlier will offset such losses. The passage you are reading is abviously trying to sell you a converter so be a little weary of the data as it is one sided. They pick and choose the data and features which compliment their sales. Nothign is absurdly false but since they don't offer a triple clutch plate lock-up assembly they show how they have had to sacrifice one for the other. (efficeincy to multiplication)
Honestly now, how many guys are buying large stall converters and NOT running a tire? We go from talking high stall race converters to street tires ... as i said before, marketing ...
Richard
The misconception of stall torque ratio is that more must be better. This is not always the case. High stall torque ratio applications, typically are for industrial equipment or engines with limited low rpm engine torque. With high stall toque ratio converters, there are important trade-offs. What you take at one end you give up on the other. Typically, a torque converter with a very high stall torque ratio, such as 2.0-2.5, will be much less efficient above its rated stall speed. There is a sacrifice in higher rpm efficiency to achieve high stall torque ratios. That lower efficiency translates into less horsepower transmitted to the tires over an RPM range.
*Lower stall torque ratio is gentler on the tires at the initial launch, but it will pull harder for the remaining 1,305 ft. of the 1/4 mile. Less races will be lost at the starting line from excessive wheelspin.
Richard
Apr 11, 2005 | 03:49 PM
#7
Thanks for your input on that Oxidizer. That was written by one of the guys at Yank.
Could you give more input on the triple disk? I'd really like to hear your input. Any advice exc. towards the topic?
Nothign is absurdly false but since they don't offer a triple clutch plate lock-up assembly they show how they have had to sacrifice one for the other. (efficeincy to multiplication)
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Apr 11, 2005 | 06:25 PM
#8
aaahhhhh. the vig triple disc lock up verter. damn i love mine. when she locks she locks. and when i want to play on the freeway i can have her lock and she will pull her *** off. here is some info.
STR has been talked and argued about for many years. The following information is what we at Precision Industries have found by doing our own testing to be helpful for you to try to understand this subject. Our competitors must have a crystal ball to figure the STR of their torque converters. There are a couple of companies in the performance torque converter business that do have the capability to test STR, MOST DO NOT! Precision Industries happens to be one that does have. Our test dyno has the capability to test from 200 ft. lbs. of torque up to 900 ft. lbs. of torque. The other companies use dynamometers that vary from 100 ft. lb. of torque to approximately 300 ft. lb. of torque. There is an old GM printed sheet that has floated around our industry for about 10 years showing the STR of stock GM torque converters that were built back then. Our competitors either use this sheet or are guessing because they have no way of knowing what the STR really is. They also advertise STR’s of 2.7, 2.9, 3.0, 3.2, etc. this is pure BS. All torque converter companies use the impellers, turbines and stators that come in the factory torque converters. In our tests we have never seen an STR over 2.55. Precision Industries do have torque converters with STR over 2.55 but these units have specially machined stators in them and are not worth the high cost for a street/strip application. If our competitors try to tell you differently just ask them to show you a picture of their test machine, not just a printout. The formula for STR is EXACT OUTPUT TORQUE ÷ EXACT INPUT TORQUE = STR. This requires a known power source and a data recovery system. STR is just what the name implies. The ratio of torque multiplication at stall. As soon as the turbine rotates (car moves) the ratio starts dropping rapidly until enough RPM has been reached for the ratio to drop to 1:1. The RPM that the ratio reaches 1:1 varies depending on other factors in and out of the torque converter such as impeller exit angle, stator design, impeller to turbine clearance, input torque (engine), etc. A fact that most everyone overlooks is that a torque converter does not make torque! It takes the torque the engine produces and multiplies it for a very short period of time. This is why some cars perform better than others with the same torque converter.
Some car enthusiasts put all kinds of money in the engine, transmission, torque converter, NOS, rear end gears, etc. then want to cripple the torque converter by lowering the STR to try and prevent wheel spin on take off. This is as foolish as pulling off one of the plug wires. Why don’t they finish the project and work on the rear suspension? Trying to tune your car by using STR is probably not very smart seeing how our competitors don’t have a clue about what STR their converters have, after all the stock torque converter you took out of your car has a STR of 1.9-1.94. The best way to get the right torque converter for your car is to buy it from a company that has a large database of previous sales for your kind of car. Then tell the sales person what mods you have made and what mods you intend to make and let that person help with the decision. The key words here are large database. The “Johnny come lately companies” have no large database or experience with what works with these late vehicles. Why try to reinvent the wheel with your hard earned money when there is bound to be someone in our database that has the same mods as you do and their torque converter/engine combination ROCKS! At Precision Industries we found out 10 years ago that STR is not the most important consideration when deciding on a torque converter it is the whole COMBINATION!
STR has been talked and argued about for many years. The following information is what we at Precision Industries have found by doing our own testing to be helpful for you to try to understand this subject. Our competitors must have a crystal ball to figure the STR of their torque converters. There are a couple of companies in the performance torque converter business that do have the capability to test STR, MOST DO NOT! Precision Industries happens to be one that does have. Our test dyno has the capability to test from 200 ft. lbs. of torque up to 900 ft. lbs. of torque. The other companies use dynamometers that vary from 100 ft. lb. of torque to approximately 300 ft. lb. of torque. There is an old GM printed sheet that has floated around our industry for about 10 years showing the STR of stock GM torque converters that were built back then. Our competitors either use this sheet or are guessing because they have no way of knowing what the STR really is. They also advertise STR’s of 2.7, 2.9, 3.0, 3.2, etc. this is pure BS. All torque converter companies use the impellers, turbines and stators that come in the factory torque converters. In our tests we have never seen an STR over 2.55. Precision Industries do have torque converters with STR over 2.55 but these units have specially machined stators in them and are not worth the high cost for a street/strip application. If our competitors try to tell you differently just ask them to show you a picture of their test machine, not just a printout. The formula for STR is EXACT OUTPUT TORQUE ÷ EXACT INPUT TORQUE = STR. This requires a known power source and a data recovery system. STR is just what the name implies. The ratio of torque multiplication at stall. As soon as the turbine rotates (car moves) the ratio starts dropping rapidly until enough RPM has been reached for the ratio to drop to 1:1. The RPM that the ratio reaches 1:1 varies depending on other factors in and out of the torque converter such as impeller exit angle, stator design, impeller to turbine clearance, input torque (engine), etc. A fact that most everyone overlooks is that a torque converter does not make torque! It takes the torque the engine produces and multiplies it for a very short period of time. This is why some cars perform better than others with the same torque converter.
Some car enthusiasts put all kinds of money in the engine, transmission, torque converter, NOS, rear end gears, etc. then want to cripple the torque converter by lowering the STR to try and prevent wheel spin on take off. This is as foolish as pulling off one of the plug wires. Why don’t they finish the project and work on the rear suspension? Trying to tune your car by using STR is probably not very smart seeing how our competitors don’t have a clue about what STR their converters have, after all the stock torque converter you took out of your car has a STR of 1.9-1.94. The best way to get the right torque converter for your car is to buy it from a company that has a large database of previous sales for your kind of car. Then tell the sales person what mods you have made and what mods you intend to make and let that person help with the decision. The key words here are large database. The “Johnny come lately companies” have no large database or experience with what works with these late vehicles. Why try to reinvent the wheel with your hard earned money when there is bound to be someone in our database that has the same mods as you do and their torque converter/engine combination ROCKS! At Precision Industries we found out 10 years ago that STR is not the most important consideration when deciding on a torque converter it is the whole COMBINATION!
Apr 11, 2005 | 06:39 PM
#9
Good info 'Nali. Doesn't coincide much with what I quoted from Yank. I like PI's feelings on working the whole setup and not reducing the s/t for a weak suspension.
Oxidizer. It would be great if you could give your opinions on proper stall torque ratios & the benefits of the tripple disk lockup exc.. offered by PI
Oxidizer. It would be great if you could give your opinions on proper stall torque ratios & the benefits of the tripple disk lockup exc.. offered by PI
Apr 11, 2005 | 07:14 PM
#10
here is some good info ;
http://www.converter.cc/truth.htm
and Yank has all it's testing done by outside co.s so the facts are clear
we give credit where it is due
We also make MULTI plate converters and have for years and have found that there is a very limited use for them,
as they are heavy, and costly, the extra weight is on the turbine and that will cause more mass to rotate and slow down off the line performance and may also requier special trans work to make the clutchs last, (Very high line settings) as they drag and this will reduce the effective STR and shift extension.
http://www.converter.cc/truth.htm
and Yank has all it's testing done by outside co.s so the facts are clear
we give credit where it is due
We also make MULTI plate converters and have for years and have found that there is a very limited use for them,
as they are heavy, and costly, the extra weight is on the turbine and that will cause more mass to rotate and slow down off the line performance and may also requier special trans work to make the clutchs last, (Very high line settings) as they drag and this will reduce the effective STR and shift extension.