I didnt notice any difference with the stock vs the aftermarket cat execpt it pulled harder from 4K to redline...

 

marksae - I can speak for others, but the UR ones meet CARB standards for emissions, while still performing better than stock in terms of flow.

 

How much louder than stock is the typical aftermarket cat?

 

I don't question their ability to meet emissions. I just question their durability as I've had a catco and carsound fail on me in the past. The catco was 3+ years old before it failed on me. The carsound was only a year old, but went through a lot of abuse. I had a Forced Performance "Green" turbo and HKS 272s that I pounded the carsound cat with daily on my GSX. I think the valve overlap didn't help since it sends out a lot of unburnt fuel through the cat at idle. Then again, I don't know how good the stock cat would have held up under these same conditions.

There have been several local DSM members that had their high flow cats fail emissions on them after 4-5 years of use also. They all say that they needed to heat their cats up before the test to pass. A good working cat should not need to be heated from hard driving to pass.

Coming from someone who has dealt with many headaches dealing w/ the Cali smog tests, my advice would be to keep a stock unabused cat on the side just for emissions. I want to get a high flow cat just to beat on.

 

Hm, there doesn't seem to be a clearcut answer if one HF cat is better than another. In this case, I think I will just go with the UR. 5 year warranty and attractive price point has me sold - while the other units look bling, $300 is too steep for something like a HF cat, IMO. I'd rather spend that on cam gears or something...