I posted a couple of weeks ago that after I installed my Y-pipe I felt no big power increase, and you all told me that most likely there was a leak somewhere; and of course there was. My question is this; since the Y-pipe's purpose is to pass as much air thru it as possible as quickly as possible, how is it that a leak affected my power? Wouldn't a leak in the pipe allow even MORE air to pass thru?

 

This response is in the category of "I think" not "I know".

It all depends where the leak is and how big it is. If the site of the leak is where the Y-pipe fastens to the exhaust manifold, there is a possibility that fresh air is actually being drawn into the Y-pipe and being swept along with the exhaust gases. The Oxygen Sensors are mounted in the Y-pipe. They would be fooled by this "contaminated" exhaust which contains more oxygen than the pure exhaust gases. The Oxygen Sensors would signal "Too Lean! Too Lean!" to the Engine Control Module. The ECM would respond by making the mixture richer. The result would be reduced engine power and increased fuel consumption.

 

Thx, that makes sense