Y8s, the cat causes 10x more resistance to flow than a louvered glasspack. It's insignificant IMO. But hell if he wants less restriction put a piece of pipe. Plus it will be lighter too.

I saw no "loss" when installed my louvered resonator. Based on boost logs only. I have a feeling the over sized 3" exhaust has something to do with it.

Louvered will be quieter despite being a LOT skinnier?

i'm just sayin, if you're going to go cat or no cat, you might as well go all the way when you go no-cat. why settle for 95%?

Jason: how much OD do you have space for? the dynomax is 4in OD.

http://store.summitracing.com/partde...5&autoview=sku

I'm running a pair of 24" core 3" ID, 4.5" OD glasspacks and a 27" core glasspack. I KNOW there's room under there. :) Loured and skinny will be quieter than the same length thick perforated glasspack. But perforated flows a little bit better. But it's negligable if you're running 3" anyways. When I was building my exhaust I tested it with the lourves pointing with flow or against it. Against it was notably quieter. I put them with the lourves against the flow.

he's running 2.5" so it might make more difference. plus he says its for track days. I think that warrants the 2% performance improvement over the 2% quietness improvement :)

I'm pretty annoyed that I killed my metal cat in < 2.5 years.

My understanding is they aren't designed to last forever. It's a compromise. More flow and you can pass emissions but they won't last as long as an OEM catalytic converter. (I hate saying cat) Sucks, but that's how it is. I plugged the stocker with the nitrous. :) No cat now. No problems.

OK I now have a louvered core 2.5" glasspack in place of the cat. Louver openings facing rear. It has a band clamp behind it so it's removable, and I can put the cat back in. The metal cat's core isn't clogged nor burned, but it's bouncing around in the shell.

I also upgraded the dented and leaking Dynomax middle resonator to a longer one by Magnaflow.

The car is quieter than ever. At cruise, top down, there isn't much exhaust thrum at all.

Exhaust backpressure is now 40-45% lower than original.