With all things being equal, mainly the stalls, except the STR of the converters, let’s say two of the same exact cars both with 3500 stalls accelerate at WOT from a dead stop, which will have the higher shift extensions? The low STR converter or high STR converter? Which will drop the RPM’s the furthest on a shift?

 

we'd need to know a lot more about the combo to even hazard a guess

 

28 inch DR’s, 3.73 gears, factory 4 speed auto, factory LS with basic bolt ons. Both cars the same except for Str. It’s very general. Which would yield less or a shorter shift drop? Low or high STR? Say a 1.68 STR vs. 2.5 STR?

 

I was about to start a new thread to encourage sharing knowledge about torque converter "STR" and how it relates to efficiency, shift extensions and more, but then I found a very thorough post on another forum that covers all this:

https://www.ls1gto.com/threads/torqu...lified.349786/

There is also a 5-year old thread here which covers the basics of torque converters very well:

https://ls1tech.com/forums/automatic...een-noobs.html

Therefore, I have renamed this thread from "shift extensions" to "Shift extension and converter STR". I also deleted some posts which are no longer applicable.

The advantages and disadvantages of high and low STR values are complicated, depend greatly on a cars specs, usage and personal preference. I'm hoping for a good discussion on it.
One question I already have is: Is it primarily a high STR which makes an e.g. 3600 converter feel "tight" or are many factors involved?
I have mention before that when I naively bought a cheap TCI 3600 converter it was loose and felt horrible on the street. But both my Yank and Circle-D converters are very tight and feel great on the road; I can accelerate moderately while keeping revs under 2000 RPM. (I could not do that with the TCI converter.)

 

I would like to share my thoughts on this topic...

However I feel someone like Dalton from FTI would be one of the Best people to chime in here First.

 

Thanks Mrvedit! Awesome! Just what I was looking for. I been trying to educate myself on this subject for a while and have it down pretty much in theory. Not practice. There is a ton of conflicting info regarding which is tighter. Low or high STR. Many say it’s one or the other. I only have theoretical knowledge and am looking to purchase a converter. I don’t want to have to change it later. I never though of checking out the GTO site. The only thing on confused about are the shift extensions. Some say the low STR hit softer from a stop but couple hard in the upper RPMS on the top end but pull the RPM’s down too far after a shift. Some say the high STR hit hard from a stop but are inefficient on the top end losing power. However, the shift extensions are higher (more slip), so it keeps you in the sweet spot making up for the inefficiency. I’m lost.

I'm still looking for and answer based on experience. Between two of the same exact cars and the same converters other than STR.

 

First I agree with vorteciroc that Dalton from FTI could help explain this and give us valuable insight.

Whether right or wrong, my approach to "high end efficiency" was to upgrade to a triple clutch converter so that it can be locked at WOT. I then tune it to lockup in 3rd gear above 100mph, which is shortly after the 2->3 shift and well above the converter's 3600 stall rpm. I think it helped a bit with ET and about 1 mph trap speed. I hope to be able to test it more this year after a 2 year absence from the drag strip.

 

What about guys with TH400’s and no lock up? That’s where I most curious.

 

STR is the measure of torque multiplication at the line when the converter "hits". Higher STR will make for a harder hit off the line and generally will have a tighter feel pulling away from a stop on the street. Some guys prefer a less hard hit off the line to minimize the risk of spinning, and thus prefer a lower STR converter. The Yank SS3600 is an example of a higher STR (2.5) converter that a lot of guys like for its tight feel. They used to make a low STR converter (SY3500 1.6) that others liked for its soft hit.

The other trade off is that the higher STR converter will be less efficient as RPMs rise to redline. So the trade-off is whether you want it on the line or at the top end.

Shift extension shouldn't be affected much either way if the stall speed is the same. Heck, shift extension was the same between my TCI SF3000/2.2 and my Yank SS3600/2.5.

 

I was an SY3500 user way back in the early '00s; this converter was quite manageable on good Z-rated street tires, and would allow for excellent traction on a BFG drag radial at max effort launch. Some folks complained about 60-foots never being good enough with this converter (hence it's low popularity - not to mention the higher cost of the SY-series). I was able to get into the high 1.6/low 1.7 range with very minor bolt-ons (on a DR) and stock 3.23s, but I know some other folks were running about ~0.05 second quicker 60-foots with otherwise similar setups and same stall speeds with higher STRs (but also stickier tires). I always wanted to try the SY4000 (I think this was a 1.8 STR) with the same setup, but never got around to it. Traction became a little more difficult at max effort after doing more extensive upgrades, but it was still pretty manageable on drag radials. I recall the efficiency rating being 97% for this converter, and I remember picking up about 1mph of trap speed with no other changes when first installed. Street manners at part throttle were excellent with 3.23s. I was disappointed when Yank dropped this series but, again, I understand that it wasn't super popular due to the higher cost and softer launch. IMO, it was the best converter series available for an NA setup where street (and street tire) traction and roll racing were top priorities. I wonder if anyone else (or perhaps even Yank) is making something comparable today?

As for shift extension, I don't recall there being any appreciable difference between my SY3500 and the more popular (in that era) ST3500 when used in otherwise comparable applications (though, admittedly, I never did try them back-to-back with no other changes). I remember the ST-series having a much higher STR than the SY-series.

 

Regardless of an individuals pedigree pertaining to competence/ aptitude for enlightenment...
I personally find that the most simple answers to relatively complex questions to be counterproductive.
I do however find in certain scenarios, my more common approach as previously stated... to instead be it counterproductive within reason.

To sum things up here... I more often, than not "Dumb Things Down" in attempt to reach a broader audience.
I apologize for this, as my doing so is most likely not always necessary.
Upon reflection, post the realization that comments made by myself were in need of deletion...
In order to limit my offenses; as apposed to sharing information in which my sole purpose of membership here is predicated upon.

I helm from a Family of Engineers and Medical Doctors... whom would be ashamed of my actions towards those, that I have deemed unworthy of acquiring the very knowledge that I LOVE to share!
From Family members who were involved in the earliest implementations of the Two-Element design Fluid-Coupling for use with very early PseudoAutomatic-Transmissions... to my Great-Uncle, that brought the 5-Element Torque-Converter to the Buick Dyna-Flow (Dual-Turbine and Dual-Stator design)...
And lastly my Grandfather (1960 NHRA Champion and record-holder: Al Zerbarini) who designed many modifications to the original "Hydra-Matic" Transmission... that would take the Drag-Racing world by storm (and was copied/ stolen by B&M Transmissions).

I have brought embarrassment to them all; and of course myself.
When discussing a more traditional three element Torque-Converter, in use with a more traditional Automatic-Transmission...

I am late to the party, in terms of providing an answer...
Now when discussing the attributes of the Torque Multiplication Ratios pertaining to the 3-Element Torque-Converters (or 4 or more Element: meaning that a Lock-Up Clutch is also used) as "STR" (Stall-Speed Torque-Multiplication Ratio). Essentially the quantitative amount of Torque produced by the Engine that the Torque-Converter can multiply for an instant by a certain Ratio to the Turbine-Shaft of the Automatic-Transmission at a specified RPM (or range within)/ Stall-Speed.

I first inform my customers to avoid inexpensive (Sub-$600 to $700) units, like the "Plague"!
Somethings are simply too good to be true... Such as a well-performing inexpensive Torque-Converter.
The difference between a B&M $300 unit and an FTI $700 unit for the same application is "Mind-Blowing"!
NEVER "Cheap-Out" on a Torque-Converter!!!

If it were up to me... I would purchase FTI units for every application that they offer (pertaining to units under 1,200 to 1,500 Ft/ Lbs in a 3,500 pound vehicle)...
Then all Neal Chance units for any application surpassing the applications that FTI covers.

Next, the "Soft-Hit" vs "Hard-Hit" terminology... along with the needed discussion on Fluid-Coupling Efficiency of a 3-Element Torque-Converter, comes into play.

-Regardless of "Popular Belief"... I describe the "Soft-Hit" units as the "Tighter Feeling" units (especially below advertised stall-speed)... act less aggressively upon the advertised stall-speed... and are more efficient above the advertised stall-speed (should put more power to the ground at peak HP on chassis-dynomometer).

The "Hard-Hit" units would be described as the "Looser Feeling" units (especially below advertised stall-speed)... act More aggressively upon the advertised stall-speed... But are Far-Less efficient above the advertised stall-speed (should put less power to the ground at peak HP on chassis-dynomometer).

Hopefully these simplistic explanations will help guide some of you in the right direction for the particular needs of projects being worked on.
While I am normally extremely busy with my personal Shop/ Business...
I am available for more in-depth/ more appropriately scientific terminology based discussions, regarding this topic.
Please message me... however please be patient in awaiting a response as I do get slammed with messages from time to time.

Again; My apologies for my unwarranted rude behavior earlier...
I do honestly frequent these forums in-order to give back to those that "Hunger" for Knowledge, in the same manor that I always have!
I actually feel quite good for a change, to speak my actual mind... and not unfairly treat you all like fools.
Thank you everyone for putting up with me! I will do my best to treat you all with the respect in-which you all deserve!

 

Great info. Thank you very much, but Just like most other threads going back even two decades on this site and many other sites, the confusion continues. The same phenomenon has occurred on this thread. This is the same phenomenon that I noticed on many other torque converter and STR threads. One person says low STR is tighter under stall and another person says that high STR feels tighter under stall.

first the high multiplication of the high STR converter is described as making the converter tighter than the lower STR on normal driving because it multiplied more torque. This results in a looser feeing low STR at low speed but tighter up top.

in the same threads, even FTI says this, the lower STR is tighter due to the impeller and stator causing the converter to stay coupled tighter all the time not letting the rpm swing up fast to hit hard, but stays efficient and tight all the way through. All while saying that a high STR is looser during low speed driving.

this has been an ongoing issue.

 

To be honest I was really trying to avoid this conversion, that being said I made a personal profile because these next words are solely my own opinion.

I do not like using STR to describe how a converter works. Due largely in part to the technology that is available to us today, the ways someone can manipulate and design a torque converter has grown 10 fold, and with that the numbers of ways a converter behaves. A prime example would be a converter I recently observed that completely goes against the "Rules" of STR and torque converters. This was a custom promod converter that only had a 400RPM fall back but showed over drive in the traps, keep in mind this was a non lock up converter. Now according to the "rules" of STR and converter behavior, that converter should have a higher STR number because it is behaving loosely(short rpm shift fallback); BUT it showed over drive in the traps, that is the characteristics of a lower STR or tighter converter. So this begs the question is it a higher STR or lower STR converter? Maybe both?

My point here is: IN MY OPINION there are far to many characteristics one is capable of building into a converter these days to limit ourselves to the definition of 1 number.

-Dalton
__________________
2011 Mustang GT, killer of MT82s
"Converter guy"

 

Wow! Thanks Dalton. Great info. I understand the reason for your account. This has been a controversial topic since forever.

I guess, in the end, it’s about the entire converter package matched to the car. I guess I was trying to stick to the mid level converters and their combinations. Not the cheap TCI stuff or custom CNC impeller and stator stuff. I’m more wanting to know when it comes to the converters made out of the common basic 9.5 6 GM impellers and 4 or so stators most builders use. Mainly the 082 stator vs the 086 stator. More specifically a converter with a negative angle impeller and 082 stator vs a positive pitch impeller and 086 stator. Both with similar stalls. Why would anyone want to use the softer hit and how would their shift extensions differ. I understand fully custom units can be exceptions, but most of us will never have custom made units other than a few factory impeller and stator combos.

 

I guess to be more clear, this is where my thought process started and why I started this thread.

its all the old posts about the old SY3500. It confuses me. It was expensive. It was a very low STR. I just don’t get it. Why buy something that will make your car take off slower from a stop? Even though they are gone, a few converter companies still build low STR units.

I read up on low STR stators and stuff and got the feeling those were reserved for cars with over 1000 hp that simply can not hook up. I just don’t understand them on the street.

people loved or hated the SY3500.

I just don’t understand the point of a converter that made your car take off slower. What would the point be? There had to be a benifits. What if a person builds a car and spends all the money and time to make it fast and, like most all of us, know nothing of converters, they call a custom builder and have the equivalent of a SY3500 or very low ATR unit unknowingly built for them. Then the car takes off slow and they don’t know why and I blame the engine and so on.... That confuses me.

There is an old thread around here where a guy specifically had a 4000 stall Fuddle (long out of business) with 1.6 STR built for him. However, he new enough about his build and converters to want that unit built for him due to traction problems. What about is regular people that don’t know how that all works and end up with a low STR unit while not knowing?

 

First welcome to the forum! It sounds like you could and hopefully will be a contributing member here.
It is refreshing to see someone, especially a new member, so clearly state that they are posting their "own opinion" and not a God given fact; this is the best way to develop a good reputation and be treated with respect.

I like that you are opening our eyes (at least us non-experts) to the idea that newer technology and manufacturing, combined with top quality materials, are able to create a converter that performs well over a wider RPM range without all the compromises of the past.
This thread is definitely moving in the direction I had hoped in which we can all learn more about converters and make better decisions for ourselves, our friends and perhaps even our customers.

 

I think the reason many users enjoy the soft hit style converters is because they are looking for a balance of WOT track performance and light pedal daily type driving. Someone like you or myself probably doesn't have a problem daily driving a 4000+ hard hit stall converter for one reason or another. We understand the "consequences" if you will for what comes with that looser converter and we are ok with it. Other users are not so they find themselves seeking out that softer hit option which allows them have their cake and eat it too.

Now there are some instances when I prefer the softer hit converter even for a more race minded setup. These will normally be behind engines that make more low end torque and less rpm or even a setup with a very larger power increase across the rpm range like a turbo or nitrous car.

-Dalton

 

Thats Dalton. He’s not new. We all know him! Been around forever. One of the most bad *** companies ever. It’s just that the STR debate is old and controversial, he he wanted to give HIS own opinion and not have it tied back to the company.

I get it. Wealth of knowledge.

 

Ah thanks.
Sorry Dalton, I did not know you were the "same" Dalton.

 

I received your PM, but I'd rather keep all the replies in this thread as it looks like it's going to be (and already is) a great conversation with lots of knowledgeable folks actively involved.

First, I must state that I am not a professional converter expert nor any kind of drivetrain engineer, so my opinions are based only on my personal user experience with any given combo.

With that in mind, I didn't actually seek out the SY3500 on my own. When I was in the market for my first LS1/4L60E converter, Yank was the big name in this corner of the hobby at the time and Mike Senia, owner, was available by phone. When I called to order, Mike asked me several questions about my goals and preferences, I told him that what I found most important was higher end efficiency/trap speed, and that roll racing was a greater concern than absolute maximum launch potential - and that I didn't plan on a tire stickier than a drag radial but would usually be on Z-rated street tires. His immediate recommendation was the SY-series, SY3500 specifically as I still had stock internals at the time. We talked at great length about the strengths of this unit and why it was ideal for my goals; this conversation took place ~20 years ago though, so I can't claim to remember all of his statements verbatim. But it was made clear to me that this unit would not result in an "underwhelming" or awful launch as compared to other similar stall speed units with higher STRs, it would just be a little less aggressive in this regard with the trade-off of better efficiency at higher rpms (which is what I wanted most).

So when you ask about why someone would choose this unit, i.e. "what's the point?", here were my reasons:

- I planned on Z-rated street tires and drag radials only (with DRs only at the track). Of course, I wanted it to perform well at the track but I was not building a drag-only vehicle by any means. So a "harder hitting" converter would have resulted in no better (or perhaps worse) ETs based on my tire choice (i.e. the advantages of higher STR would be moot but any disadvantages, such as lower efficiency at higher rpms, would still apply).

- Roll racing/peak HP/trap speed was greatest concern to me. Mike never stated nor alluded that shift extension would suffer nor improve in any significant way based on the higher or lower STRs of his various offerings at the same stall speeds, just that the SY-series was ideally suited for my goals in all aspects.

So it was with my eyes wide open that I chose this unit and I never expected, nor desired, to set any 60-foot records in so doing. My goals lied elsewhere, and this unit did not disappoint. With that said, and as I posted above, I was still able to get this combo to 60-foot in the high 1.6/low 1.7 range on a well prepped track with max effort launch on a DR (full weight T/A, very minor bolt-ons, 3.23s), and it would endlessly burn street tires if I simply "shocked" them off the line - so it was not a "dog" at launch by any means. But, again, other folks with otherwise comparable setups using the ST3500 (with much higher STR) would typically 60-foot about ~0.05 seconds quicker from what I recall. As mentioned above, that's the best ET comparison I can provide as I never did swap between these converters back-to-back in the same car with the same setup and gears.

General street manners at part throttle were excellent with the SY3500, it did not feel too "loose" to me with 3.23s nor was it overly slow to get moving from a stop at throttle tip in (the car would still roll by just releasing the brake from idle speed). But I do recall the higher STR units of same stall speed feeling a bit tighter at part throttle with the same gears. This aspect is highly subjective though, and no "top shelf" converter of ~3500 stall speed or less has ever felt too "loose" to me on the street. Some folks are much more bothered by this, so it's hard to guess at any one individual's threshold in this regard. As for me, the SY3500 felt perfect and I had no regrets about its part throttle performance/behavior. From what I recall, shift extension seemed very comparable to the other cars I drove and raced with ST3500s, but I honestly was not making specific notes on this aspect at that time. In any event, shift extension (relative to the stall speed) was NOT disappointing by any means with the SY unit.

I know that much of my summary is anecdotal as I didn't do comprehensive back-to-back comparisons on my application or others but, as mentioned by Dalton above, modern converter design could make any direct comparison of ~20-year-old SY3500s vs. ST3500s somewhat irrelevant as it applies to something built/bought new today anyway.

I do hope this helps and touches on all the concerns you mentioned in your PM.