L10 torque converter questions...
05-17-2005, 02:18 PM
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L10 torque converter questions...
I'm about to install K04s, DPs, ICs, etc. and have several L10 questions.
From discussions with several of you, it seems that the TC upgrade is the most important of the L10 upgrades, particularly for those who don't plan to go for max hp and torque. Any other opinions/thoughts?
What stall speed is recommended and why? What difference will I feel between a stock stall speed of 2,000 and, as an example, 2,500? Will, an upgraded TC slip less and allow the car to build speed more quickly?
Thanks for any answers or suggestions.
From discussions with several of you, it seems that the TC upgrade is the most important of the L10 upgrades, particularly for those who don't plan to go for max hp and torque. Any other opinions/thoughts?
What stall speed is recommended and why? What difference will I feel between a stock stall speed of 2,000 and, as an example, 2,500? Will, an upgraded TC slip less and allow the car to build speed more quickly?
Thanks for any answers or suggestions.
05-17-2005, 03:32 PM
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Higher stall = more heat
So cooling is even more critical with a L10 tip transmission.
A higher stall speed will allow for better brake-torque launches. You will also use some more fuel since the stall speed is higher as well. More slippage = less efficient.
I have yet to get my car but I am not sure if TC replacement gets rid of that hunting issue around 40mph.
Overall, I donâ€<sup>TM</sup>t know about the TC being the most important of the upgrades. Though it is the most important to install CORRECTLY. The TC isn't the limiting factor of the tip transmission, it is the internals that are.
A higher stall speed will allow for better brake-torque launches. You will also use some more fuel since the stall speed is higher as well. More slippage = less efficient.
I have yet to get my car but I am not sure if TC replacement gets rid of that hunting issue around 40mph.
Overall, I donâ€<sup>TM</sup>t know about the TC being the most important of the upgrades. Though it is the most important to install CORRECTLY. The TC isn't the limiting factor of the tip transmission, it is the internals that are.
05-17-2005, 03:49 PM
#3
Answers ... (thanks for posting our email)
The torque converter is made from sets of rotating fins that act like a viscous fluid coupling. One of the reasons why they call it a "slush box" ! But the TC fluid pump actually stores & amplifies flywheel energy, and can make for stronger launches at lower RPM's than our 6sp brothers (who seem compelled to do crazy things like dropping the clutch at 5K).
At low speeds the friction of the fluid conveys very little torque from the engine to the tranny, and so the TC "slips" allows the engine to idle and rev, while the car is stationary - the tranny is in "D" and foot is on the brake.
As RPM's increase the fluid flowing on the fins of pump side start to interfere with the fluid motion caused by the fins on the turbine side, and when Stall speed is reached the TC "engages", and the tranny catches-up to the engine.
Higher stall speeds allow the engine to rev higher before the TC engages. This allows faster and smoother launches.
If you set it too high then a) you have to rev high to go, and hitting the boost curve on every start from stop will feel like a race launch everytime (i.e. jerky) b) the TC will slip excessively when cruising streets at low speeds in high gears, which again creates unnecessary stress.
Set the TC too low and the engine has to work harder from low end of the (no Turbo spool) torque curve, the fluid is heated more and if you do power launches with too low stall speed it will overstress the engine, TC and tranny.
(BTW: Once above 50mph there is a lock-up clutch that bypasses the fluid coupling and makes a direct connection between Engine & Tranny)
The stock TC is 2000 rpm. Many folks in the first L10 upgrades got 2800, the latter folks got 2500.
The fins of the OE TC are flimsy, and simply bent into place. I know of one TC destroyed on Stage 2, with 100 oct, so I think this is a key weakness.
L10 out-sources their TC work. They take your OE TC and have the fins welded into the body, as well as re-calibrating the fins and re-balancing (so they say). There are 3rd party TC's available e.g. from B&M racing, but I don't know if they fit and don't know of anyone who's tried them.
I originally had 2800, but got it lowered 2500 during a L10 service trip - I found this to be silky smooth, even on stock s/w - it should have come like this from the factory ! If I did it again I might try higher, but 2500~2800 appears to be the sweet spot.<ul><li><a href="http://auto.howstuffworks.com/torque-converter1.htm">Laymans' TC Explanation</a></li></ul>
At low speeds the friction of the fluid conveys very little torque from the engine to the tranny, and so the TC "slips" allows the engine to idle and rev, while the car is stationary - the tranny is in "D" and foot is on the brake.
As RPM's increase the fluid flowing on the fins of pump side start to interfere with the fluid motion caused by the fins on the turbine side, and when Stall speed is reached the TC "engages", and the tranny catches-up to the engine.
Higher stall speeds allow the engine to rev higher before the TC engages. This allows faster and smoother launches.
If you set it too high then a) you have to rev high to go, and hitting the boost curve on every start from stop will feel like a race launch everytime (i.e. jerky) b) the TC will slip excessively when cruising streets at low speeds in high gears, which again creates unnecessary stress.
Set the TC too low and the engine has to work harder from low end of the (no Turbo spool) torque curve, the fluid is heated more and if you do power launches with too low stall speed it will overstress the engine, TC and tranny.
(BTW: Once above 50mph there is a lock-up clutch that bypasses the fluid coupling and makes a direct connection between Engine & Tranny)
The stock TC is 2000 rpm. Many folks in the first L10 upgrades got 2800, the latter folks got 2500.
The fins of the OE TC are flimsy, and simply bent into place. I know of one TC destroyed on Stage 2, with 100 oct, so I think this is a key weakness.
L10 out-sources their TC work. They take your OE TC and have the fins welded into the body, as well as re-calibrating the fins and re-balancing (so they say). There are 3rd party TC's available e.g. from B&M racing, but I don't know if they fit and don't know of anyone who's tried them.
I originally had 2800, but got it lowered 2500 during a L10 service trip - I found this to be silky smooth, even on stock s/w - it should have come like this from the factory ! If I did it again I might try higher, but 2500~2800 appears to be the sweet spot.<ul><li><a href="http://auto.howstuffworks.com/torque-converter1.htm">Laymans' TC Explanation</a></li></ul>
05-17-2005, 03:50 PM
#4
I think the TC is the weakest part - it's died before other parts.
Rumour has it the only difference between RS6 tranny and the S4 is the upgraded TC.
But I agree that keeping ATF at the right temp is also of key importance - it shouldn't be too cold (causes the tranny to slip) or too hot (ATF will bake and take years off tranny life). As soon as I've proven I have the Aux Cooler setup perfected I will post a tech article with photo's.
But I agree that keeping ATF at the right temp is also of key importance - it shouldn't be too cold (causes the tranny to slip) or too hot (ATF will bake and take years off tranny life). As soon as I've proven I have the Aux Cooler setup perfected I will post a tech article with photo's.
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05-17-2005, 10:24 PM
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How dose B&M work?
Is it as effective as you expect?
I just ordered the same ATF cooler and thermstatic valve from B&M under Michael's suggestion. Do you have any problem in installation?
Jimmy
I just ordered the same ATF cooler and thermstatic valve from B&M under Michael's suggestion. Do you have any problem in installation?
Jimmy
05-17-2005, 11:25 PM
#10
Installation was a pain - I am not sure if the standard routing will work
This is what it should ideally look like
<img src="http://pictureposter.audiworld.com/58573/atf_cooler_second_attempt.jpg">
I installed the thermostatic switch under the radiator support
<img src="http://pictureposter.audiworld.com/58573/img_1757.jpg">
cut out enough to route it all out to the front
<img src="http://pictureposter.audiworld.com/58573/img_1758.jpg">
where it looks like this
<img src="http://pictureposter.audiworld.com/58573/img_1756.jpg">
But an air-pocket in the cooler may be the cause of my leak. I haven't confirmed if the switch is working, or if I need to change the routing.
<img src="http://pictureposter.audiworld.com/58573/atf_cooler_second_attempt.jpg">
I installed the thermostatic switch under the radiator support
<img src="http://pictureposter.audiworld.com/58573/img_1757.jpg">
cut out enough to route it all out to the front
<img src="http://pictureposter.audiworld.com/58573/img_1758.jpg">
where it looks like this
<img src="http://pictureposter.audiworld.com/58573/img_1756.jpg">
But an air-pocket in the cooler may be the cause of my leak. I haven't confirmed if the switch is working, or if I need to change the routing.