MOTV8 Posted November 10, 2011 Share Posted November 10, 2011 a.k.a. your basic hydrodynamic fluid coupling ...how do they work? What is stall speed all about? Lock-up? How do they affect driveability? Are they a good bang-for-the-buck performance mod? Discuss... Link to comment Share on other sites More sharing options...
NicD Posted November 10, 2011 Share Posted November 10, 2011 Torque converters are voodoo magic, seriously... As far as bang for the buck if you are doing drag racing it's one of the best bang for the buck things you can do and it's generally required when you go aftermarket camshaft because of the higher idle speed required and smoothness when letting off the foot brake since a cam (well any worth putting in) is not smooth at idle. Stall speed is what RPM it will hit if you hit the gas from a dead stop and you actually have traction. Note this is dependent on power levels and the torque curve and is an estimate in ALL cases when looking at torque converters for sale. Any torque converter out there for corvettes is going to have lockup assuming the factory trans does. They will constantly slip more than factory when not locked up meaning the RPMs will be higher when putting around town but how it drives is highly dependent on the stall torque ratio of the converter and it's stall speed. Here is one of the best how it works basics on the internet for torque converters. http://www.howstuffworks.com/auto-parts/towing/towing-capacity/information/torque-converter.htm Link to comment Share on other sites More sharing options...
MOTV8 Posted November 10, 2011 Author Share Posted November 10, 2011 Voodoo magic indeed! Thx Nic, I love mine, easily cut .6 in the quarter mile times, and I haven't noticed any difference in driveability around town. I did have to 'relearn' to launch the car, as I was able to 'flash' the converter to a higher rpm at the tree so when it hooks I get my best 60's and e.t.'s. Is there anything you have to do differently when you're tuning a car or dyno'ing one with a non-stock converter? Link to comment Share on other sites More sharing options...
Jon Posted November 10, 2011 Share Posted November 10, 2011 Gears and a torque converter will make an auto car feel like a whole different vehicle. The trade off for a stall converter is lower in town MPG. Highway mileage usually stays the same since you are locked up. There is actually a clutch inside the torque converter that allows a direct coupling between the engine and transmission. GM has really smoothed the engagement of the clutch over the years. Old 700r4 trans had such a dramatic lockup that it felt like another gear. That's because the converter is providing some amount of slip and when you engage the lockup clutch, that slip goes away. A stalled auto is also very fun to drive. Which leads to even more decrease in mpg, lol. You always want to romp on it. Link to comment Share on other sites More sharing options...
FNBADAZ06 Posted November 10, 2011 Share Posted November 10, 2011 Yank SS3600 convertors are the silver bullet for the 6L80E C6 guys.....damn, can those cars launch hard and record awesome 60' short times Link to comment Share on other sites More sharing options...
NicD Posted November 10, 2011 Share Posted November 10, 2011 Is there anything you have to do differently when you're tuning a car or dyno'ing one with a non-stock converter? That heavily depends on the model/year and what is done to it. It ranges from nothing required to major changes. Link to comment Share on other sites More sharing options...
Two Fangs Posted November 11, 2011 Share Posted November 11, 2011 how do they work? Essentially, your first statement is correct,they are a fluid coupling. Think of the toque converter consisting of two desk fans pointed at each other. With one fan plugged in, and blowing on the other,what happens? Naturally it begins to turn. Essentially this is the premise behind a torque converter. One engine driven "pump" (the plugged in fan) drives a "turbine" (the fan that is not plugged in). What is stall speed all about? Stall speed is actually comprised of two different stall ratings;Flash stall and Full stall. If you had a way to completely lock the transmission, like a trans brake, full stall would be found by by matting the gas pedal and monitoring your RPMs. So if you had a 3800 RPM stall and a a trans brake, you would rev the engine and it would stall at around 3800 RPMs (this would also be your launch RPM). Many people will try to stand on the brake and gas at the same time (brake stall), and think that is full stall. While it can be full stall, typically it is not, as in this method, the observed stall is limited by the traction of the tires and the torque curve of the engine. Flash stall is measured by letting your engine idle and then slamming the gas. Typically you will see a bit more stall for a split second as the acceleration of the engine's rotational mass "flashes" the converter a small amount above the actual or "full" stall rating. Lock-up? Going back to our "two fans" example above, the fan plugged in will always move slightly faster than the driven fan because of frictional and mechanical losses. If only we had some sort of mechanical means to lock them together... Alas, we do, the torque converter clutch, or TCC. How do they affect driveability? Torque converters with higher stall speeds typically take more RPM to get the vehicle moving, since the point of maximum torque multiplication within the torque converter is moved upward in the RPM band. The streetability of a high RPM stall converter is similar to exhaust. It is a matter of preference based on the concessions the driver is willing to make. Are they a good bang-for-the-buck performance mod? Yes, probably the best mod you can make on an automatic transmission equipped vehicle. Link to comment Share on other sites More sharing options...
MOTV8 Posted November 11, 2011 Author Share Posted November 11, 2011 Self hijack: What magic is it that Ed Coan for instance or Yank do differently in the construction of their converters that make them more "preferrable" to racers? Also, since the torque multiplication increases does a car dyno differently with all other mods the same? I think I've read or heard that high stall autos are hard to dyno accurately??? Link to comment Share on other sites More sharing options...
Two Fangs Posted November 11, 2011 Share Posted November 11, 2011 OK, so now we dig the rabbit hole a little deeper. Lets talk for a minute about our "fans" again. We initially talked about them to discuss basic torque converter function. Now, let's introduce another component. This component goes in between the two fans and redirects the air to ensure the air from the plugged in fan hits the fan that is not plugged in with more force. This component exists within the torque converter and is called the stator. Through the use of a stator, we can multiply torque from the pump to the turbine. Stator designs differ and this changes the amount of torque applied from the pump to the turbine. Essentially, by changing the amount of torque multiplication we are changing the ratio of effort between the pump and the turbine. This can be expressed as output torque divided by input torque. This is called the stall/torque ratio,or STR. STR is temporary while the car is stationary against a foot brake or a trans brake. Once the vehicle starts to move, STR approaches zero as both halves of the converter rapidly approach the same speed. The higher the STR, the harder the converter will hit the tires and help 60 foot times, at the expense of converter efficiency and MPH. The lower the STR, the slower the 60', but the better the MPH on the big end. Since the STR is short lived,and most readily experienced at launch, it is not typically something that affects dyno results in an observable fashion since the car is already rolling when the dyno run begins. As far as high stall converters and dynoing, yes, cars with sloppy converters are harder to get accurate dyno results with. This is kind of an inherent problem with dyno design, and not the converter itself. When the car is rolling on the dyno, and the operator accelerates the car and hits the sample button, in a single revolution of the drum, the dyno looks at the RPM of the engine and the MPH of the car and calculates a final gear ratio. Since a high stall car's pump and turbine are probably not close to 1:1 (unless the tuner locks the torque converter clutch) the final gear ratio are calculated incorrectly. This skews the dyno results. Link to comment Share on other sites More sharing options...
Jon Posted November 11, 2011 Share Posted November 11, 2011 I had a 5200 FTI converter in my GTO. With the transbrake engaged it was 5200rpm. That car only dyno'd at 430rwhp, but moved a 4000lb(with me in it) GTO to 11.5004 at 118.8mph with a 4200ft Density Altitude. Nic tuned that car on the street. Link to comment Share on other sites More sharing options...
Pete K Posted November 29, 2011 Share Posted November 29, 2011 Self hijack: What magic is it that Ed Coan for instance or Yank do differently in the construction of their converters that make them more "preferrable" to racers? Also, since the torque multiplication increases does a car dyno differently with all other mods the same? I think I've read or heard that high stall autos are hard to dyno accurately??? Quality, effeciency, and design are the 3 primary $$$ determinations. Some use billet back halves. Stator design has improved greatly over the years, making them, super efficient.Similar to the improments that have been made in turbo design. Fins, pitch, weight etc. Limited quality aftermarket parts (for converter internals) does not help to lower parts cost. Link to comment Share on other sites More sharing options...
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