After installing our dual exhaust on our '06 LS 2.2L automatic back in march '10, our HHR is experiencing symptoms of a clogged catalitic converter.

1. Loss of power when climbing a grade/hill and needing to pass a slower car on the highway at a cruising speed of 2500 RPM or lower.
2. Exhaust leak type sound present when excellerating, from the front end.
3. Loss in overall gas mileage.

Had various muffler shops inspect for a exhaust leak as we were convinced there was an exhaust leak, but to now availe. no one could locate any leak at all.

Our dual exhaust system was based off many other HHR owners here on the forum with a split to go to the right side muffler, just right before the left muffler. we've installed imco turbo mufflers with the intent to not have a loud exhaust but did not intend to have such a full blown low restrictive system either.

Could this style system be the cause of all our problems? Has anyone installed a different configuration? if so pls share how it was done.
We've noticed the right side has much less pressure coming out of the tailpipe as opposed to the left side. So it is really uneven as far as a dual system goes.

Anyone have any ideas/suggestions for a cure to our HHR's Illness? Thanks for the help.

 

Any time you tap into an exhaust, like a "T" the flow will be greater to the path of less resistance., aka straight thru like stock.

In other words exhaust gasses don't like to make 90* turns, if a path is open straight ahead.

Also depends to a degree, on how well the tap-in was done.

This design is not a true dual exhaust, just at the ends, it looks that way.

However- this should NOT be causing any problems ..

1) fix the ex leak up front..

 

Any chance you have photos from under your car? And do you have pics of how you cut the rear for the second exhaust tip?

 

The leak sound could come from the splitter and not actually be leaking, just "whistling" where the split is. As for the loss in performance, maybe your cat is giving out. Adding the duals should have had nothing to do with this and wouldn't cause the performance loss unless it was very poorly done. Have you taken it back to the shop that did the work?

 

I don't know how much in this case, but any time you slow the exhaust gas velocity, you decrease cylinder scavenging, when you do you hurt low speed torque. people say you need some back pressure, no truth at all to that, back pressure is always bad, but you do need exhaust gas velocity, the more the better to a point. The reason some cars feel more torque with resistive exhaust than free flowing is because the free flowing system they have is either too big or poorly designed so it slows down velocity. Exhaust must be properly sized and shaped.

 

initial questions would be: "Did it just start doing this? Did it get progressively worse? I assume it was fine for the few months after the install? How many miles on the car? When do our cats give out?

 

It started a couple months ago with only the exhaust leak type sound and did get progressively worst. Now you have to mash down on the gas pedal to maintain speed even on a slight hill/grade.
Our HHR has just under 80k miles on it as we take it to disneyland quite often.

 

Any chance Mickey was trying to make a break for it and stowed away in your tailpipe?

(Sorry, couldn't resist)

 

Next time out check and see how hot the cat is.....usually when they fail they really throw out some serious tempertures......doubt it had anything to do with duals...they too far back to matter anyway..

 

Our HHRs' run very lean stock, an exhaust leak up front could cause it to run leaner yet.
Hope you didn't burn any valves. That would take away power. Perhaps a compression test, or a Leak-Down test would tell how things are inside the motor.