Ok, I think I'm misreading your post. Are you asking about running a 3.5" y-pipe under a lowered car or are you asking about running any size y-pipe under a car that has been lowered 3.5"? A 3.5" y-pipe is overkill unless you're making a ton of power, and a car lowered 3.5" would put it below street level, wouldn't it?
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