[align=left]Alpha dog if It wasn't a blizzard here in the D I'd record a m-peg of my Alpha with dual s.s. magnaflo(straight -thru) exhaust and no resinator. It has a slight gurgle and growl. Much improved from stock but far from what it should be. I'll get it posted a.s.a.p
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I don't know? Looking at those pics I think you only have 2 cats, normally they do not put an O2 sensor after a muffler/resonator. As IK stated you need heat on the cats and that Giant Resonator Can is to far from the heat and no O2 sensor by it. The GM Dealer Techs are not necessarily always right. If you are so worried about back pressure why are you wanting to change your exhaust? Replacing the muffler will affect your back pressure.

 

gunny...after his last pissy reply I wouldn't try to help him anymore...how many times does a man have to say it....umm...ok. Ya know what? I was a gm tech for years too..

 

Ok, why is having 4 catsa bad thing?

It's my understanding that by separating the converter in to multiple stages, itincreases its effectiveness which allows it to be designed with less restriction.

If I'm wrong, please explain.

 

well...what some people don't want to understand is that the cats ARE NOT MONITORED!!! Look in the pics, there are upstream 02 sensors in the manifold collectors....nothing after the pre-cats...which means with no downstream 02 sensors to monitor exhaust gases then the cats are obviously not monitored and can be replaced with better flowing ones or just gutted. Sure in proper terms there are 4 cats...but pre-cats aren't really big restrictive cats like most people think of when they hear catalytic converter....like was mentioned before they are just there to heat up super fast to aid in start up whne the real cats are still to cold to filter anything.

Unless a pic is posted that shows evidance of downstream 02 sensors then I could care less what a gm tech with the title as me says.

 

Today I went to a local muffler shop that specializes in custom bending for custom exhaust systems. He lifted my H3 Alpha and this is what we saw. There are 4 cats, two on each side before the collector, I don’t know if they are both monitored but the technician said they must stay (NYS law). After the collector was the resonator (mid truck), he said we could replace that with a new muffler with dual tailpipes exiting out the back of the truck.

Of course it would take some custom bending to maneuver around things underneath to exit at those indentations at the rear bumper with my choice of polished stainless tips. He had three different stainless mufflers to choose from, quiet, semi-loud and loud, the system included all stainless pipes, stainless welding rod, stainless hangers all installed for and guaranteed $660+tax. He could have done the job right on the spot but I didn’t have 3 hours to kill so if I want the job done I’ll have to go back. He also said he’s already done several Alphas and they have turned out great!

 

yea, monitored or not they are mandatory in certain states to pass inspection...not really the smog part but the visual part. Plus I've heard of cops in NY checking underneath for cats.

 

Patches Quote: "The driver's side "pre-cat" or "pup-cats" as they are also known. There is one of these coming off each of the exhaust manifolds, driver and passenger, just after the O2 sensor. The pup-cats light off faster than the main cats to keep cold start emissions low."

Thanks for the pics Patches!!!! a big help. My concern was I assumed (wrong) that the manifold CATs would be monitored, but as we have discerned, none are??? Like IK posted in CAPS [:@] back at post 54. So, if your state laws allow removal or replacement of at least the pipe cats (the second set) to high flows, it may?? be of some benefit sound and performance wise.

Gunny, I agree...........what a friggin mess!IK, the flat spot in the I5 exhaust, ain't that flat.

If it were me, I would wait for an aftermarket CAT back kit, they are almost set to be released, (see MAGNAFLOW H3 Alpha Exhaust - Very Close to AVAILABLE!!!!)and if after installing one I needed more sound, I would add high flow CATs to replace the second set.

 

sorry doc...I can't see the pic that great, for some reason the screen on my laptop is like half the size of the screen with two big black bars on each side of it. my 17" laptop screen is now about 6"...I have to figure out how to fix it...driving me nuts!!!!

I think the guy that removed the flat section of pipe in his I5 was Hunner? not gunner...hunner. I don't think he has posted here lately.

 

I guess you can't leave well enough alone, to throw a wrench in this I would see if the MAC 5.3 headers fit, wait for the Magnaflow. I know for those who start changing stuff to soon then all of a sudden the aftermarket catches up, BAM! "I just wasted my money because of my impaitients." Plus I am glad I live in SC no sniff, no nothing and only 1 licsense plate.

By the way REAL nice Vette exhaust in that link.