Originally Posted by MrFatbooty
What you fail to realize is that the cat is only part of the exhaust system.
I'm well aware that the exhaust funtions as a "system".
Look at the flow difference between the stock cat and a test pipe. Yet when people running a test pipe along with an intake, header and exhaust put their car on a dyno they get very similar results to what they would get with the stock cat.
I assume that since you request dyno proof of my argument that you have charts to support this (though I suppose "similar results" is rather subjective and could be argued)?
I'm not saying that the stock cat cannot be out-flowed, the point is that given what the rest of the exhaust system is able to flow even with bolt-on mods that the cat doesn't slow anything down.
If an upgraded cat-back is able to flow more than ~220 CFM (which a well-designed one should, considering that a length of 2.25" piping can flow 400+ CFM and that there are systems which have shown only a 2 WHP loss over open-header), then the cat
is a restriction. From your statements, are you arguing that the rest of a modified system
can't flow more than the OEM cat, even considering its absurdly small inlet and outlet?
Also, the "not-so-recent header test" you're referring to was on an ITR which is already putting out 25 hp more than a GSR and benefits more from increasing the exhaust flow.
Yes, the test was on a basically stock ITR, although the C1 and C5 are not so different that they will not react at least similarly to exhaust modifications (as header builders can attest to).
But on a stock LS or GSR motor with a bolt-on header and exhaust and relatively new stock cat, replacing the stock cat serves not much purpose.
Again, I contend that it is
at least as cost-effective as replacing the header and cat-back.
Also, I do hope you realize that our discussion shouldn't be perceived as anything more than a friendly, intelligent debate I think it benefits the entire forum when members are able to read and/or particpate in these discussions, and hopefully come away with a bit more knowledge. :beer: