How much to slip the clutch to not damage parts

[Chris Hill]

How long does a racing clutch need to slip to not damage rest of powertrain?

By clutch slip, I mean how long from time clutch is released by driver until 100% clutch lock-up.

100% clutch lock-up is defined by ratio of engine rpm/driveshaft rpm is a consistent number until gear change.

Should it be 0.05 sec, 0.1 sec, 0.5 sec, or longer?

Not asking for clutch tuning secrets, just trying not to damage everything else during the learning curve.

[Dwight Southerland]

Chris -
This is all just my opinion based on my narrow little experience so take it with prejudice.


If you are asking in reference to the CC, you will find that the majority of the resources available do not have a lot of history with low hp-torque applications. That means that you will have to build your own knowledge base. Low hp heavy vehicles tend to break parts more than high hp vehicles. (Not enough power to control the clutch; higher gear ratios mean smaller pinions; etc. etc.) Here's some stuff to always consider:
1. The clutch cannot be the sole agent of slippage to get the vehicle moving. That's the reason they make tires engineered for stick applications.
2. Learn how to build you own pressure plates and assemble the tools necessary to blueprint them.
3. Disc material is a huge area of study. Unfortunately, our culture has all but eliminated asbestos from the mix, so it will be hard to find a good rag formula that will endure the heat of slippage. The metal and ceramic based materials are harder to make consistent in round-robin racing conditions.
4. Winning rounds is much more important than going fast so as a last resort you can campaign for a Dana 60 in the truck.

[Sean Marconette]

Chris,
Do you have a data logger? The rule of thumb is from the time the driveshaft starts moving til the engine and input shaft are at the same speed. More than 0.6 is too much, and less than 0.15 is not enough. This is just the launch. Each gear change you want to see some slide, particularly high gear. Base adjustment is for the launch, and CW adjustment is for high gear lockup. But CW will impact the base adjustment. How much the clutch is pulling the engine down is another factor too. Not sure if this is helpful or makes sense. There is also too much slip that can glaze the disc, and it will not lockup the same after being glazed.

Sean

[tj310]

http://www.umtrnorth.com/forums/topic.asp?TOPIC_ID=7090 Link to some clutch graphs ---Trevor

[Chris Hill]

Originally Posted by tj310

http://www.umtrnorth.com/forums/topic.asp?TOPIC_ID=7090 Link to some clutch graphs ---Trevor

Thank you. It's a closed forum and I've applied for membership.

Hopefully can see it soon.

[Chris Hill]

Here are videos from last night testing.



What do you think about the slip? Too much, too little, just right?

All runs had clutch fully locked after 0.05 seconds per the racepac. Time equals zero one data point before driveshaft starts to move.

[Sean Marconette]

It defiantly sounds like it is pulling the motor down a bunch!

Sean

[tj310]

First 2 passes too much base pressure locking it up too soon , 3rd pass after dark sounded better. (may of spun the tires more)
Our base pressure is pretty well Zero when the car is cold you let the clutch out and nothing happens till you rev it up a little and the centrifugal weight starts to kick in , sorta like a go kart. Once it's warmed up a little it grabs sooner.
--Trevor

[69Cobra]

Chris "victorymotorsports" you have been approved on the UMTR forum

[John Duzac]

Seems to me that you need to come out harder. 6500 to 7000. If you are already at that launch rpm, pump up the tires some. Bogging badly and loosing a lot of et. May could use more first gear, like a 3.25 or so...