I was wondering how much louder will my truck get with High Flow cats? I have gibson duals now and it sounds good but I was a serious rumble even at idle. And which brand to get??

 

I bought a pair for my Mustang from Bear River Converters - Wholesale distributors of catalytic converters.

If your truck has 4 converters and you remove them and install 2 high flow units, it will be somewhat louder. If you replace all of the stock units with high flow units, it won't sound any different.

 

He is right. My truck came with 4 converters, and I replaced them with 2 high flow units, and it sounded a lot better, and that was with the stock exhaust it had on it at the time.