That Product Specialist is probably not familiar with converter terminology. I used to work for B&M and I even interviewed with TCI (now work at T-netics). STR is nothing new, I have SAE paper work that demonstrates early converter development from Mopar and GM, which talks about selecting the appropriate STR and how it affects driveability.

Every converter company (actually designer) knows what Stall Torque Ratio (STR) is, and there is no other meaning for the abbreviation STR, in regards to torque converters.

FYI: If you measure the torque at the flexplate (say 300 lb/ft) and compare it to the trans input shaft measured torque at the true stall (say 600 lb/ft), that would be an STR of 2.0. Now you can only measure true stall by holding the input shaft RPM at zero rpms and going trying to go as many RPMs on the converter as possible. Although that rpm is heavily dependant on the output of the engine (measured flexplate torque), the higher at the flexplate/ engine output the higher the reading/stall will be. I used to test several converter combinations with B&M's converter dyno and I was able to fully understand the effects of different Impellers, Stators, Turbines, etc ... on the rated stall and STR of a converter. This is one reason why Vigilantes are believed to be under rated, they rate them at a different torque level then most. Typically converter makers will test converters at 300-400 lb/ft of torque, which is similar to the method GM used to test them at (not sure if they still do it this way).

As for Yank and the 1.6 STR, it was found on their now-out-of-production SY3500. They probably have not updated that tech page in a while. The lower the STR the looser it will feel, yet be more efficient up top. The higher the STR, the harder the hit on inital launch and tighter it will feel, yet be less efficient up top. This is because the multiplication is greater at low RPMs with a higher STR, which results in more (available) torque at the wheels, yet peaks and tappers off sooner.

 

Thanks for understanding my question.

From what I gather, PI actually has the equipment to check the STR of any converter, and this is how they select their parts.
But there are a handful of companies that use whats worked in the past, for example a customer wants x.xx str with x,xxx stall speed. Certain companies look it up in a book and just select the parts, verify fin angle, assemble the converter and ship it out.
Would you say this is close to an accurate statement?

I've seen a local shop do it. A Master Book, fin angle tool, and the parts.

 

Not sure, as we always put our converters on a converter dyno and verified the results, prior to production release. Although there are companies that do hokie ****. I know Yank and PI have converter dynos, not sure of the others.

 

I had a SY3500 with the 1.6 STR and the car would sixty foot in the low 1.6's on DR on a crap track. It felt loose but it was way better then the 3200Vig I replaced-I could never get the Vig to hook on DR's. The Yank was worth 3 mph up top over the Vig Too.

Now that I own a C5 with over 900 rwhp, I would love to get a converter with a low STR so I can launch the car without destroying my output shafts or diff on the starting line.

 

Thanks guys.

 

Good stuff! I'm trying to learn, but there seems to be alot of conflict surrounding STR? For me anyway
I like hearing discussions from people with real experience through actual usage vs. theory. Theroy is good for the initial builds along with engineering, but nothing beats trial and error.

 

Well I asked to see if anyone on here has a converter dyno. If they don't (which I don't think anyone does) then they are making different stall speeds using different parts listed in a book. My local core rebuilder can do that, I've seen the book.

If no one replies to my question here I'm taking my money and using it somewhere else.

Does anyone think it's weird that certain companies jump all over guys that have no clue?
They post up a transmission problem that sounds like their trans is shot, and EVERY site sponsor replies.

I'm not experimenting with multiple $800 converters, sorry.
I believe in 2009 there should be a company out there that can get it right the first time.

 

It's a trade off. The SS3600 is a popular converter because it puts the engine right in the stock powerband and with the 2.5str is fairly tight around town. It'll hit like a mother off the line as well (better get GOOD tires). It'll be less efficient up top.

I'm thinking of upgrading to a PT4000 with a 2.1str. It will still hit hard down low (it doesn't have as high of a str, but the higher stall should make it still hit about the same as a SS3600) and it will be better from a roll (more efficient up top). It will feel looser around town though being a low str.

 

So the lower the STR number the looser the converter will feel when driving around? I thought it was the other way around. I guess I was wrong. Learn something new everyday.

 

It doesn't make sense to me? If the stock STR of 1.89 is as close to 100% efficiancy you can get, then i would think moving away from 1.89 would make the TQ feel loose?? Of course at WOT a higher STR would have a greater multiplier, making it bite harder at launch, probably feels better on the *** dyno? Now at light throttle, my sense would tell me a higher STR will make the TQ feel loose due to the low efficiancy. HMMM, i better get a book and start reading.

 

That's the way I understand it, I could be wrong though...

 

This is exactly 100% how I thought it worked too. Can anyone verify this for sure?

 

i have a yank PT 3800 2.0 str. i would not call it loose at all. at idle on perfectly flat concrete it is right where it wants to start creeping on its own (with the car idling in drive). i can stay under 2500 rpms just cruising around. i have very little time on it yet so i don't want to say more than this for now. for my needs i could have bought a stall that was a fair share looser than this one from how it seems so far.

 

Let me help. We personaly rent race tracks and test different converters about once a month. We tested 6 different converters just this past sat in Bradenton motorsports park in FL. Put 1 in make a run then swap and make another so on. This gives you real world results. This is the comitment we give to our customers to find the ultimate in converter technology. We test cinverters behind 1800 hp Top sportsman cars,Top dragster,Ls cars,low7 sec turbo cars etc. These tests put the proof on your time slip. Products dont become low qualifiers and win national championships built from a chart but from hard work and comitment to qaulity.

Greg

 

Thats what I thought so why is everyone else talking about a 2.1 STR converter being looser than a 2.5 and so forth, its the other way around. A 2.5 STR converter will hit harder off the line and be looser driving around town, but will be less efficient on the top end than a 2.1 STR converter. The trade off as to why a looser higher STR converter can still win races is because races are won at the 60' mark. As we all should know a good 1/4 mile pass is all in the first 60' of the track if you run a tire that can hook it.

As a side note I have a a SS3600 with the 2.5 STR and it will barely move at all if I am at idle with the car in drive. If the road I am on is uphill at all or not smooth the car will not creep forward on its own, I would consider this considerably "loose" compared to the stock 1.89 STR.

 

The reason I've been asking so many questions is because STR means something different to just about everyone you talk to.

And I started a thread here asking the converter builders to basically prove they have a converter dyno. I got this idea after googling and finding something on PBA's site written by PI about STR, how other companies test for it, and to outright ask to see their converter dyno so when you see they don't have one you know they're not building converters properly.
I've come to the conclusion that STR is pure BS. Same with converter dynos.
Unless you're building converters just to run on a converter dyno.
For us, the consumer anyway.

I think the answer is real world experience builds a converter, not a converter dyno.

I still don't know why only one converter builder replied to that post.
I think because he's the only one that has the confidence that he can build me a converter that will perform the way I want it to.

I've read so much about converters I've come to the conclusion that a good builder will get you what you want.
I sent a PM to the guy that replied. The conversation we had was short and to the point. Like one guy(me) knows what he wants and has specs, the other guy knows exactly what to do to build a converter to get me there. Simple. I can't wait til next Monday.

 

Well I am sure that any one of the good sponsors here for us will build you the converter you want if you just call them and talk to them about what you want. Just call them.

As far as the STR being BS, it basically is the ratio of how much torque is multiplied within the converter. There are differences in how people describe it yes but overall its the same thing. If you want a converter thats going to hit hard down low but not be as efficient up top then go with something 2.5 or higher and if you want something thats easier on the tires but more efficient on the top end then go with something lower than 2.5. From what I have read about it thats really all there is too it. I am still pretty sure a 2.5 STR converter is going to be looser feeling than the 2.0 converter on the street though.

 

why dont yall send a link to this thread to Circle D, Performabuilt, etc? If you dont get a reply then you have your answer. Ive been through Circle D conveter chop, they built theres with a CNC i saw running and hand make the rest of it. Dunno bout this master book or a converter dyno but there tc's have a good rap.

Fyi thanks for asking 9000th this is the **** this site is here for

 

So i take it you got your answer and got a converter coming on Monday from FTI.We will have to go back out to PBIR to test it out.Now we need to get you some tires.

 

Can FTI, circle D or one of the other manufacturers explain how different STR's affect the same converter? I know that STR is only one piece of the combination.

Correct me if this is wrong but my understanding is you can't directly compare STR from one converter manufacturer to the next because there is different combinations in building a converter that will give you similiar characteristics.