I am not 100% sure yet, but I think I have a leaking manifold gasket. Its not noticeable until you punch down on the accelerator, then you can definitely hear a louder air noise. I did put on a K&N CAI last weekend and think the noise is definitely more pronounced than just after I added it. I checked it out yesterday and all of the connections are still tight. I'll check out the exhaust thoroughly on Sunday. My questions are, if the gasket does need replaced, would this be a good time to change over to a new SS Exhaust header and If so, and it is still good, would you reuse the existing down pipe or just replace that and catalytic converter at the same time? Money is always an issue but I would rather spend it now than be working on it again in six months. 2010 HHR LS Panel - 2.2L 72,000 miles. Thanks

 

Check the flexpipe. That's the part that usually fails/cracks 1st.

The link below has some good info and pics.
https://www.chevyhhr.net/forums/how-...ex-pipe-31536/

 

X2 flex pipe, the headers aren’t going to give you much, without a tune.
As for the down pipe, I went with a 2 inch stainless pipe and opened up my car back to a 2 1/4 inch Walker system.
It doesn’t have that drone on the highway
The down pipe is mandrel bent unlike the kinked OEM pipe