Nol Not in any way. Do a search on this site for "turbo muffler" and it should turn up a lot of reading. We have tested several "performance" mufflers on the HHR and the IMCO T-924 is the best performing to date. There is a video clip of the sound, compared to stock, HERE.

The HHR's Ecotec engine likes to see a certain amount of back pressure for the best mileage and performance, and most "performance" mufflers are too free-flowing to provide this. That leaves the car running sluggish and falling on it's face under normal driving conditions. Mileage suffers with these other mufflers as well, as lower back pressure requires you to "keep your foot in it" more to hold speed.

The best part about the 924 on the HHR is that there is very little "resonance" while cruising, unlike the "fart cans" you are familiar with. It provides a deep, throaty tone on startup and at idle, and a "healthy" sound under normal driving conditions. When you really floor it, the 924 puts out a nice sound that is not loud, but clearly says; "I'm not stock." It's also lighter and more compact than the stock "aluminum turtle" and looks much cleaner under there.

I have had a bunch of mufflers and cat-backs on my HHR, but keep returning to the T-924. Coupled with the CGS intake it provides a winning combination.

Hope it helps,

 

Well, I have not checked, but last time I did most manufacters recommended changing the filter every 3-6 K. And most Jiffy Lubes check it for ya, and try to sell you one.
So, old school or not, I have ran K and N in every vehicle since 1999 and I have had four trucks, two SUV and now the HHR. I never had a problem, and the filter lasts!! Costs less in the long run too.
50K for a filter change is way much IMOP. I looked at this one with 1200 miles onit, and yes, it looked clean, duh, but I shook a lot of debris out of it. I live in the desert, so it is real dusty here almost all the time, so changing the filter often is a good thing. And at $3 a gallon for fuel, I think it is a cheap maintenance tip also.
So $40 for a free flow filter once compared to $12-$20 every 4-6 months, It pays for itself in one year.
If we get any MPG increase, that is a plus, although I dont foresee this actually happening.
But after looking at the two filters, The K and N is SO MUCH More Free flowing!!!

AS for the CGS, I don`t know if the MRS. would want that just yet. But everyone here is praising it, so it must be doing something better.
Question now is, what MPG did you get after installing the CGS only?