I've heard they are good (necessary?) if you are road racing or driving under heavy stress for long periods. Never had one on any of my Vettes...
Catch Can ???
Race Director
Joined: Jan 2005
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From: Bay Shore, NY 11706 MILD2WILD (M2W)
St. Jude Donor '06-'07
On todays motors all the crank case vapors are recycled into the intake to be burnt in the combustion process. A catch can catches any oil that is in the vapor and stores it for disposal. You would be shocked at the mess in the intake from the oil 
Race Director
Joined: Jun 2000
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From: Hurst, TX USA
Pro
Joined: Feb 2007
Posts: 741
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From: Kennesaw GA
I had one on my SVT Lightning but that was a supercharged motor. I had no idea that naturally aspirated motors would ever need one. I had to empty the Lightning's can about once a month, about 1 oz each time. Any idea how often an LS2 needs to be emptied? I remember a major factor was driving style. For instance, I took the SVT to the drag strip a lot and the more WOT runs I made the faster the can filled up. Daily driving hardly ever deposited any oil in it.
Safety Car
Joined: Dec 2005
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From: North Carolina
St. Jude Donor '07-'08-'09-'11-'12
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From: Bergen County, NJ
When I swapped my stock intake manifold for a ported I/M, I had oil on the bottom of the stock I/M. The oil made its way down to the portholes. So I installed a catch can.
I do, however, do high revs, and maybe that's why the oil seeped thru.
I do, however, do high revs, and maybe that's why the oil seeped thru.