just looking for some opinions on these things. i have heard that without hi-flow cats you dont get much out of headers. at what horsepower do these start to make a difference?

 

Every expert I have talked to says that the stock cats on the 99+ trucks will outflow most hi-performance mufflers. Flowmaster is the most noteable company whom's mufflers are outflowed by the stock cats.

In other words, for hi-flow cats to give you ANY performance gains at all the stock cats must be the most restrictive part of your exaust. Which it is my understanding that in 90% of cases they are not.

Your exaust can only flow as well as its most restrictive component, and if it happens to be the cat's then and only then will you see a gain from the cat's alone.

Also remember that our engines require at least some backpressure to make low end power, so too much flow can be a bad thing.....

Summary: What you get out of headders is not affected by the cats, unless they are the most restrictive part of your exaust.

 

I am about to take my cats off. My truck pulled hard when I was going to the muffler shop with straight headers. I didn't feel any loss down low like I did on my Dodge.