LS pistons do not have large enough valve reliefs for VTEC size intake valves. You can get away with using stock VTEC cams because they do not have enough lift to cause an interference issue. After market cams have more lift and will most likely cause P2V contact.
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Honda-Tech > TampaRacing
TR "Old Skool EF" Member #666
All motor 1.8L: 201/140 More coming soon 
I mount an balance 24" tires for $40 each.