What would the difference be if I run a H pipe w/ hi flow cats vs. the stock h-pipe with the rear cats cut out and have pipe welded in? Will there be any flow benefits between the 2? The car will never see more than 300 hp. The car is a 93 GT bone stock down to the silencer.
The cats in an aftermarket pipe are freer flowing that the stock units and the pipe is a larger diameter. Also, if you have emissions inspections where you are, it very possibly won't pass with just the pre-cats on your car. Given the fact that your car is bone stock, neither is a really worthwhile mod by itself at this point.
Well I'm starting with the exhaust first and then going to the engine with the exception of 4.10's. I just didn't know which way to go because I'll be doing all the exhaust at the same time.
I'll be leaving the first set of cats on but replacing the rears. The only thing that makes it "HACK" is the job you do on it. I'm pretty good with a wire welder so it won't be thrown together. A HiFlow pipe is the same thing just not pieced together. Will they not do the same job, basically? I just don't see paying somebody else to do the same thing I can dofor not a 1/4 of the price.
I'll be leaving the first set of cats on but replacing the rears. The only thing that makes it "HACK" is the job you do on it. I'm pretty good with a wire welder so it won't be thrown together. A HiFlow pipe is the same thing just not pieced together. Will they not do the same job, basically? I just don't see paying somebody else to do the same thing I can dofor not a 1/4 of the price.
No they wouldn't do the same job, seeing as a hi-flow cat still has the core, abling the exhaust gases to be catalyzed into its cleaner forms. It simply flows better than a stock unit, but doesn't do any less emissions work, the government wouldn't allow them to be sold otherwise.
Technically, on the stock h-pipe the two pre-cats are there to quicken the heating of the O2 sensors to operating temperature. They are not cats in the traditional sense.
Now the reason others are calling it a 'hack job' is that on a stock h-pipe, you may see a 1HP increase (I'd bet more like a 1/4HP), but almost guarantee failing emissions testing. So it's a 'what's the point?' scenario.
If you are truly 'doing' your exhaust I'd leave the stock unit alone, and purchase a good mandrel bent X or H pipe. Get an off-road one if you don't need to worry about emissions. At least here you might see a 2HP increase over mandrel piping with cats, and they are cheaper sans hi-flow cats.
Another option is just busting out the stock cats. You will still have to cut the pipe to get to the back cats but it'll leave a cleaner look than peicing everything together. But your best bet if money isn't an issue, spend 150 to 200 bucks and buy an offroad pipe. But that alldepends on where u live.
I vote for buying the right pipe vs modifying your stock pipe.
I'd keep the stock h-pipe intact. You never know when you might need it. I have a stock h-pipe i keep tucked away just in case because i have an off-road h-pipe.
Another option is just busting out the stock cats. You will still have to cut the pipe to get to the back cats but it'll leave a cleaner look than peicing everything together.