importkiller,
I really don't know much about it andI'm going on what my guy at the shop told me. Check this out here: https://www.hummerforums.com/m_130027/tm.htmAre you saying that the muffler looking thing midframe is actually a resinator? Couldthe Alphaactually have two cats and two resinators? I'm going to a New Hummer Owners Seminar on the 27th and maybe I can ask someone about that.

rhill20,
Samesame here! It's nasty out otherwise I'd go take some photos of the exhaust system and post them but I don't feel like laying in the snow.

 

unless there is a picture of the system it's hard to say. I just don't see how a cat would work that far back...cats work on heat...they need heat to get the "waffle" inside to do their job of filtering out the nitrogen. On a cold car the cat does absolutely nothing until it heats up, this is why most are placed as close to the motor as possible without getting it so hot that the element gets burnt up. Automakers have played with the idea of using an electric heating element to have the cat already warmed when you first start your car but nothing has come of that....so that being said I don't see why GM or any brand would put a cat that far back in the system cause it wouldn't work. There was actually a company making a high performance exhaust for the new lancer and they swore there was a cat right by the rear axle till I took mine off and cut it in half...it was just a resonator, just like I assume is on the alpha. ...My guess without seeing it is that there are two cats in the manifold...not really traditional cats, new technology, then there is a mid stream cat with a up flow sensor then a resonator then the muffler

 

Would there be a reason NOT to go with the Dual Extreme? The one where the tailpips come out on the sides (one on each side). Was thinking (I have one of those trailer hitch baskets) that it would be better so as not to melt my cover on the basket carrier.

 

I really have to take the camera out and get under the Alpha...but it is waaaay to windy for that today!!

I think I am just going to build my own system. Catback, flowmaster 40 or 44 placing it where the res is now and running strait out the pass side (like the H2 aftermarkets).

 

kinda like what I had on my Dodge



I like that setup...looks cool IMO

 

I like that set up, but not sure how much room is there to run the driver side strait out? Has anyone seen (at least on the Alpha) what GM did to get the pipe over to pass side pipe???? I've gotta take a picture of this?!

 

there's no spare tire back there or fuel tank, should be easy to bend a pipe across to that side.

 

It sounds like the exhaust on the mid 90s Mustang with the 4 cats right after the exhaust manifolds.
Resonators usually come after the muffler, if the're before the muffler then there is not much to them and act more like an expansion chamber.
If you have O2 sensorsforward andaft of the cats then you will have problems with hi-flow cats with the CEL.
You might want to give it some time before chopping up your exhaust, I mean the Alpha just came out. Pics would help greatly though.

 

that's not really true about resonators coming after the muffler.....ALL import cars that have the can muffler at the bumper have a resonator near the rear axle. Same thing on the old chevy beretta, there was a cat, resonator then can muffler at the bumper. Most cars with rear mounted mufflers have a forward mounted resonator...look at the link Doc gave for the I5 exhaust and you'll see a forward mounted resonator then the rear mounted muffler.

 

That's exactly the one I'm talking about.



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