Ep. 5 Torque Converters 101: What Is Stall Speed?

[Music] hi welcome to Tech Talk with Hughes performance I'm Pete Nichols today's episode is pretty exciting it might be one that you've all been waiting for and we're gonna answer the question what is stall speed so if this is your first time tuning into our Channel go ahead and hit that subscribe button in the lower right corner check us out on facebook we're uploading new content daily check out our website we have our catalog uploaded there it's huge performance calm over 1,300 new part numbers for 2019 and we're constantly coming up with new stuff as we go thanks for tuning in so getting right into it stall speed is the maximum amount of impeller rpm that can be achieved without the turbine physically moving it's important to note that stall speed is not a fixed number so if you have a torque converter that has an advertised stall speed rating of 3000 rpm that converter is not going to provide 3000 RPM of stall speed in every possible application that it could be used in the torque converter is a load sensitive device and this is universally true there are no exceptions to this rule in the automotive industry a torque converter is going to respond with a varying stall speed number based on the torque output of the engine the vehicle weight the gearing in the rear axle the rear tire diameter or in the case of a front-wheel drive vehicle the front tire diameter gear ratio and the transmission all of these factors contribute to the maximum amount of stall speed that can be achieved with a torque converter so that same 3,000 stall speed rating that we're talking about in our example could be put behind your basic 400 horsepower small-block engine in a 3,500 pound path your car with a three-speed automatic transmission and a 373 rear axle ratio and it's probably going to provide you right in the neighborhood of 3000 RPM of max stall speed you can take that same torque converter you could put it in a 5,000 pound truck with a big-block engine and again a three-speed automatic transmission and a 342 rear axle ratio and maybe a 31 inch tall tire and depending on the torque output of the engine this same converter that normally has an advertised stall speed rating of 3000 rpm could potentially provide as much as 4,000 rpm or more of stall speed so you have a pretty wide window of stall speed that can be achieved with any given torque converter based on the application that it's being used in now stall speed is a little bit of a mixed bag as far as nomenclature goes because it's not a fixed rating there's actually different ways to define stall speed we commonly refer to three different areas when we're talking about stall speed one you have foot brake stall speed that's the amount of stall speed that the torque converter can achieve when you have the brakes fully engaged and you're applying the throttle against the converter without the vehicle providing any forward motion or without overpowering the brake assembly and the wheels turning foot brake stall speed is universally going to be lower sometimes significantly so then your advertised stall speed rating of any given torque converter the reason for that is the torque converter is multiplying your engine's output torque as it's multiplying torque you're delivering more foot-pounds of torque to the rear axle you have a ring and pinion that is providing torque multiplication from the gear ratio so you're say 400 foot-pounds of torque 2,000 rpm could be six or 800 foot-pounds of torque that's actually trying to be applied to the rear tires by the time the converter multiplies the torque that torque is multiplied through the ratio of the transmission and then further multiplied by the axle ray go in the rear end as such you're gonna have so much torque at such a low rpm you're either going to physically override the brakes capabilities of withstanding all that torque or you're going to override the coefficient of friction that's available between whatever surface you're on and your tires consequently the tires are going to start spinning foot brake stall speed has nothing to do with how accurate a converter has been built in terms of function or performance or what stall speed it should be providing foot brake stall speed doesn't give you any real relevant data or anything useful in terms of how your converter should be reacting to your combination if you bought a torque converter that has an advertised stall speed rating of 4500 rpm and you can only foot brake it to 1800 rpm that doesn't mean that the converters built wrong or in any way defective that typically means that you have an engine that doesn't make a lot of low speed torque or you have a lot of ratio between the transmission low gear and the rear axle ratio and again that's one of those things that it's just not a good indicator of converter performance or function so if you're concerned about the amount of foot brake stall speed that you're seeing with your converter give us a call so that we can talk about your combination and help you understand what's actually going on front to rear in the car why you're seeing that number we're ready to talk to you and help explain it so that it all makes sense you can see that the converter actually is doing its job the second parameter we discuss when talking about stall speed is flash stall speed flash stall speed is the amount of rpm that you can observe when the vehicles in a rolling condition to low speed it's typically easiest to check it and second or third gear obviously you want to do this on closed course where you're away from other people you don't want to hurt yourself or others you don't want to get in trouble with the law by doing this out on the street but you can be rolling along in your vehicle to low speed and second or third gear say five to 10 miles per hour and just quickly transition to white and throttle while you're observing the tachometer wherever you see your tachometer swing up - in terms of rpm reading that's a good indicator of your flash stall speed that's a much more useful figure to gauge how the converters functioning what type of performance the converters actually capable of when we're talking stall speed we most frequently talk flash stall speed when we have you on the phone or communicating via email we're gonna want to know that number the third parameter that you have is static stall speed and that kind of goes back to the beginning of the video where that's the max amount of RPM the impeller can achieve without the turbine physically moving and the only way that you're ever truly gonna know the absolute max static stall speed of any torque converter is to either have the drive wheels permanently locked so that they physically just can't turn which is obviously really difficult to do or to have a trans brake in your transmission if you have a rev limiter you're gonna have to disable your low-speed rev limiter so that you can observe this you can put the vehicle on the trans brake you can go to wide open throttle for just a second and observe how much stall speed it can be achieved without any Rev limiting capabilities and that's gonna give you an accurate idea of the max static stall speed that your converter is capable of this is also a very useful figure when we're talking converter performance and converter function so you just want to pay close attention to advertised stall speed ratings and don't make your converter choice based on advertised ratings even if you've just got a basic combination a street rod or a pickup truck I mean you could have a tow vehicle where we do have a shelf stock regular joe entry-level converter available it's still worth your time to call us or shoot us an email and get that recommendation so we can help fine-tune your converter selection process you're spending good hard-earned money to buy our products you're getting a good quality product we want to help you achieve the maximum amount of satisfaction with your vehicle and with our products and to do that we need to know what you're building what the converters and we're happy to talk to you so that you get the right product the first time so what creates stall speed well stall speed is primarily influenced by impeller fin angle clearances that are set up inside the converter during the converter build and stator design what you see here is a variety of components from the general motors 245 millimeter torque converter family this is a really common core to use in street performance converter builds all the way up to high horsepower drag racing converter builds it's a super versatile core they're readily available pretty much everybody in the industry uses this core for a wide variety of their product offerings it's very versatile because general motors produce six different impeller options with different vane angles and as you can see five different stator options with different vane counts and vane angles and vane shapes so we can tune the 245 core to a very very broad expanse of vehicles power outputs and stall speed requirements getting into the actual angles and shapes you can see in the impellers here that starting with the lowest stall impeller that GM produced in this particular core you can see the impeller vane it stood fairly straight up in the inner and then transitions to a very positive angle at the outer drive tip generally speaking as we have a straighter vane in this area and a more aggressive Bend towards the outer tip we're going to experience lower and lower stall speeds we typically experience higher ratios of drive within the converter for improved efficiency as well as we move into the medium stall impeller compared to the low stall impeller you can see we're still stood fairly straight up on the inner here but it has a much less aggressive positive move as it transitions into the outer tip angle this impeller is going to stall higher than this impeller moving through here we have a more negative angle shape you can see that the veins have a bit more negative sweep to them and come up to a more neutral position again that's gonna provide a corresponding increase in stall speed this is basically the same style impeller as this but GM took the outer tip of the impeller main and stamped it so it has just a very slight positive sweep so this particular impeller basically kind of splits the difference between the medium stall and low stall and pillars and then we get into the high stall in colors and you can see in both of these examples they have progressively more negative impeller fin angles as we go more negative on the angle we increase stall speed the reason for that is the negative angle traps more fluid at the outer tip because it traps more fluid at the outer tip it requires more rpm to get the impeller to flow fluid to the turbine to get the turbine begin moving if you go back in our first episode you can see the electric fan example where the powered fan begins turning the unpowered fan on same concept as we change this angle we need more centripetal force pushing that fluid to the turbine to get that tournament or fan to spin we can also change stall speed with stators we have the five different stators here and this is just a small example of stators that we have available because of our CNC machining options and our fabricated steel stator options we literally have a innumerable amount of stator options to tune your converter program again we're using the GM 245 family here just because it's a really good visual example for a wide variety of OEM options that provide a significant range of stall speed so we have the 18 vanes stator this stator is commonly referred to as a 681 casting you have the GM casting number here this is the lowest all-stater you can see that it's got a relatively steep pitch to the veins pretty wide window area flows a lot of fluid 18 veins it's got really good torque multiplication characteristics this is the popular and well known zero a two stator again based on the casting number also an eighteen vane stator but it's got less dramatic vane angle as we start to roll the stator main angle over this is about fifty degree this is roughly 45 degree we're closing that window area so we're increasing resistance to fluid flow through the stator we therefore see an increase in initial stall speed this is the one zero two stator this one's kind of rare this is a factory heist all stator you can see it's got very little window area very aggressive fat rounded ramped vane shape this stator is going to give a lot of stall speed but it's also not very efficient very very few builds rely on this type of state are typically really small displacement high rpm low torque output applications we have what's called the 682 stator this is a fourteen vane big window area now normally you think this would be a low stall stator because of the big window area between veins and the low vein count but it's actually considered a highest all stator because it has a very very shallow pitch to the vanes so this stator design and similar models out there to it you have very good initial flash characteristics but because they have a big window area once that stall speed has been achieved they start flowing a lot of fluid they're a very efficient stator stators of this type tend to work good in turbo cars where you need to transition into a high RPM and don't boost quickly but then you need a converter to lock up tight and then finally you have the 391 stator again this is a little bit of a rare bird the 245 family twenty-one vain very thin veins fairly shallow angle again this is a heist all-stater flows a lot more fluid than this stator does so it's going to be more efficient and with the extra three vanes compared to your 18 vanes Staters it's going to add more torque multiplication when it comes to the stator design as we increase vane count we increase torque multiplication we have more vanes available so a more surface area available accelerating that fluid back to the impeller so we're creating more drive force because the window area is smaller by the space that's physically taken up by the extra mains it also provides more stall speed again due to restriction through the standard fluid flow just the resistance that's created so fluid starts flowing efficiently through it moving the other way we can go to lower main counts on the stator and we're gonna decrease torque multiplication and we're gonna lower stall speed from the bigger window area low vein counts are typically necessary in extreme high horsepower combinations if you get in nitrous cars big horsepower turbo car as blower cars even really large cubic inch you know seven eight nine hundred cubic inch plus engines that are naturally aspirated you're gonna see stators used that have lower vane counts in much bigger window areas one you have a lot more torque being applied so you don't need as much torque multiplication provided by the stator and two you're putting more torque to the converter it's naturally going to stall higher because you have higher input torque so you have to manage that torque with your impeller vane angle design as well as your state or design we mentioned clearances when it comes to converter builds I can take an impeller I can take a stator and I can physically increase the clearance between the impeller and stator and we're basically creating an inefficiency in the converter an internal fluid leak so to speak it's going to increase stall speed I can also increase clearance between the stator and between the turbine and basically achieve the same thing now I can build a properly clearanced converter where I'm maintaining good overall efficient operation but I can go into the stator and I can start to remove material from the impeller side of the vanes I can open up that window and I can shorten the overall height of the vane and I'm actually going to tighten the converter because we're reducing resistance to the fluid flow through the stator and we are lowering the point at which the converter can achieve an efficient fluid coupling conversely I can take this same stator in the same properly clearanced converter and I can machine the turbine side of the vanes I can either come in here with a mill and I can create a flat or I can actually shorten the overall height and I'm actually increasing stall speed and the reason for that is it requires more centrifugal force more rpm to get that fluid flowing through the stator those type of state or modifications are really common in the industry when you get into C&C machine Staters you don't see as much of that type of machining taking place because we're basically starting clean sheet and we can make the stator do whatever we want we can incorporate any vane count we can incorporate any window area any pitch angle and fine-tune the stator right from the get-go without additional machine work same holds true and our pro SSX fabricated steel Staters we're building it from scratch we can do whatever vane count in vane angle we want our pro SSX stators are typically our most efficient highest flowing Staters fantastic choice in any max effort combination our Pro Series stuff can be used anywhere from a street car to a Top Sportsman application everything in between so we just we have a lot of versatility in our custom converter builds when we get into turbans and how turbans affect stall speed not really much going on there for the most part turbans being the driven element the element that's turning your input shaft and therefore providing drive to the drive wheels don't really affect stall speed nearly as much as your impeller main angles and your stator designs do we have seen in testing that we can alter this inner vane angle a bit and have some effect on stall speed and coupling characteristics but to be honest we just don't have enough good data on it yet to even really justify trying to fine-tune stall characteristics via the turbine we pretty much just rely on this and this is true of just about any builder out there to just be the simple driven element that delivers power to the rear wheels so that basically as what's going on with stall speed if you have any questions you can ask those in the comments below we'll be happy to interact with you online you can shoot us an email on huge performance comm we have a tech form you can fill out for a custom convertor recommendation or just a general contact form and we'll get right back to you and give us a call at 877 Sacrement message through our facebook page we'll respond immediately we look forward to talking to you we have four very experienced very professional sales staff just waiting to talk convertors with you and help you make an educated decision if you have an off-brand converter that you want checked out or stall speed tuned on we're happy to do that as well you can shift it to our facility and we'll let you know what we can do so look forward to our next episode be sure to hit that subscribe button and tune in as we continue our converter series [Music]

Channel: Hughes Performance

Views: 141,065

Rating: 4.8779144 out of 5

Keywords: Hughes Performance, components, drag racing, Converters, Torque Converter, Circle Track, XTM Series, XFM Series, Performance, Full Race, Transmissions, Components, Gear Sets, Deep Pans, Oil Pumps, Flexplates, Valve Bodies, Oil Coolers, Assemblies, Kevlar, Kolene Steels, Bearing Kits, Service Maintenance Kit, Valve Body Kit, Transmission Kits, Transmission Box Kits, Teflon Ring Kits, Basic Overhaul Race Kit, Race Box Kit, race products, Racers, Racing, Race Cars, Race Parts

Id: 4NDvsgheq-8

Length: 21min 49sec (1309 seconds)

Published: Thu May 23 2019