I just got an HKS Hi-Power cat-back and a Mil.Spec high flow cat. Car is loud. How much of a reduction of noise would I get by putting back the stock cat?

 

It would be a little bit quieter.

 

It's gonna be a little quieter but if you really want it quieter, you might want to look in to adding resonators.

 

Thanks for the quick response. It was the drone that is the problem and in the thread in this forum discussing the HKS Hi-Power, that was never an issue that was brought up, so I am assuming the drone is coming from the cat. My Evo X is the first one I have heard with an exhaust and this sounds like an amplified exhaust leak (it sounded like a Toyota with a hole in the flex pipe on the exhaust X100). Is that the normal sound? Loud cars don't bother me (I've had a 2JZ-GTE powered car catless with an HKS Hi-Power and an STi with exhaust...then later equal length headers and thought that they sounded great), but this was bad.

Thanks for all the help on this...just a little frustrated.

 

Check for a leak then maybe all the bolts aren't tightened.

 

ugakirk makes a very good point. For a span of several months I had difficulties with the bolts backing out on my exhaust and leading to very loud and obnoxious exhaust leaks. Solution....I welded the connectors.

 

Put the stock cat back, car sounds great...but now I got a boost leak to find.

I have to tell you, the car did not like that high flow cat. My intention was to get this put on, then do a Melon tune...but oh well, I'll stay with the stock cat.

So now I need to make a thread for "Help me find the boost leak", and a thread to sell the cat.

Anybody want a Mil.Spec high flow cat with only 10 miles on it? $300 shipped.

 

Any decent high-flow cat is going to be louder than the restrictive OEM cat. I've got the MIL-SPEC cat pipe and love it. To dial back the exhaust noise I had an 18 inch Vibrant Performance resonator installed on the long pipe of the cat-back exhaust. You can go that route.