I want to add a duel exhaust system to my 2007 H3 for better performance and gas mileage but a few people (mechanics) said that in order to get the best performance from it, i need to put on an aftermarket header, aftermarket catalytic converter and then the duel exhaust system. They said the header I have now needs to be larger to allow more exhaust to flow and the catalytic converter will allow the same. They say without enlarging the whole system, I am defeating the purpose. I also will be adding a K&N Cold Air Intake. Are they right in what they say or will I just be wasting money putting all that in?

Thanks

 

This has been discussed numerous time on this forum. I would suggest you do a search and include the keywords Cold Air Intake and Dual Exhaust. I think you will find the answers you are looking for.

 

On many vehicles, your mechanics would be paritally correct. Oftentimes an aftermarket header gives better flow than a stock manifold, but in the case of the Atlas motors the manifold is not a significant source of constriction in the intake/exhaust equation. The I5 simply isn't capable of increases in power to the degree of warranting upgrades of the exhaust manifold.
Dual exhaust on a single bank exhaust motor such as the I5 is redundant as far as performance goes. You can get all the airflow the motor can possibly use thru an aftermarket single outlet exhaust system or free-flow muffler. Duals just look cool and sometimes sound better.

Your best gain for this motor would come from a combination of a free-flow intake, free flow muffler or complete exhaust sysytem, and a PCM re-program.
Without the re-tune, the computer will not take full advantage of opening up both ends of the system.

 

For me it was AirDoc's intake, K&N filter, ported throttle body, engine coil spring deletes, GM touring exhaust (is dual tips, one muffler) and the PCM tune with a shift level of three. I did all this to make up for the loss of power that putting 35 inch tires caused.

There are others that have put the header on and like all of the other changes, believe there was a small gain. Really the header is removing the first CAT and is just freeing up the small amount of restricted HP that is there. The bigger question is does all of this additional cost for each of these upgrades worth the gains?

Would I do it all again? In a heart beat!