Exhaust Headers & Catylatic Converter

[N2DIRT]

I have an 06 H3 Adventure about 76K miles. It's completely stock, runs great, completely paid for! Since waranty is not an issue nor do I have to meet any emisions checks, I am considering replacing the exhaust manifold with a custom header for the I5, and possibly removing the catalystic converter. Will this require a mod or replacing the CPU? If anyone can provide any information I would be greatly apreciative.

great forum, Too bad Hummer is almost history. I have watched on the sidelines for years.

[wpage]

Hi and welcome. I put a header on my o6 with the 3.5 no problems. There is a pre cat on the exhaust manifold that will come off. However there will still be another so your emisions should be no problem.
If you do a search I think you will find added info on this topic.
Good luck!

[N2DIRT]

Thanks WPAGE, I did the search and read through the thread you had posted about the Exhaust header install that you did on your truck. Good information! That was about 2 years ago, looking back what are your conclusions; You had concluded you could definately feel some new HP, but what did it do for your MPG? Knowing what you know now, would you reccomend this as a DIY for someone realtivly mechanically inclined? Have you considered removing the cat converter downstream from the header & replacing with a section of pipe?

I am planning on keeping my truck until the wheels fall off, but would like to make a few improvements for a little more power, and a little better fuel efficiency. Thanks for the reply.

[wpage]

You can do it. The transmission dip stick and some of the nuts are tough but its doable. Leave yourself a day and start early...
As far a mpg its hard to say I later added a billy boat performance exhaust performance air and hydrogen booster so its all muddy water. I opted to leave in the cat since here in NJ the regs are difficult.

You will notice better low end performance with the header

Have fun!

[N2DIRT]

Thanks again for the information. It sounds like a good Summer project - while I have a few days off, and plenty of time to leisurely get it back together. I will probably take the Cat converter out and have a piece of pipe fabricated to fit in it's place, bolt up to the new exhaust header flange. I'm a bit concerend about the impact on exhaust temps, possible impact on the O2 sensor(s) and how the CPU behaves. Down the road, if I decide to sell it, it would be failrly simple to return it to stock or give the original parts to the person that buys it.

[pdsq99f4]

I'd be warry about the rear exhaust manifold to head bolt breaking off in the cylinder head. It may already be broken. You can reach back behind the heat shield and feel for it to see if it is. It's a real pain to drill out and rethread. Just a heads up.