Pretty much spot on. Only thing I would add is to reinforce the fact that
PSI does not directly equal power. PSI is a measure of pressure, or specifically resistance to flow. It does not measure flow. I see this mistake way too often. If you have a shitty flowing system, you're going to see higher PSI, but not necessarily more power.
Anytime you go Forced Inducted, you want to prioritize a good flowing exhaust, and yeah can't imagine Stock Cats designed for an NA application would help with that. The goal is to get more air in, and just as quickly get more air out.
I don't care if I lose a pound or two of boost, I care about what it'll do to the response and power curve if I free up the exhaust, and do it in a safe reliable manner for my application/circumstance, hence my plan above.
Quote:
Originally Posted by Jayhovah
I am, by no means, an expert in this stuff.. but I always thought the benefit of back-pressure wasn't really the pressure itself, but the increase in exhaust gas velocity in the lower rev range (which you want for scavenging purposes)... this is why you lose low-end torque if you go way oversized on your exhaust pipes. I think keeping the velocity in a good place is important for both NA and SC, but you have to factor in the big increase in exhaust volume when you go SC.
No matter how you slice it, the OEM cats are an enormous restriction and are not beneficial to making power. Otherwise, few people would buy HFCs or test pipes.
You might see more boost with OEM cats, that is only because flow through the motor is being restricted... without them, boost pressure likely reduces and power will absolutely increase. Often times this is a misunderstood concept and you will see people wonder why their car makes less power at the same boost pressure compared to another with a different setup.
Moving on, I have read many times that the heat, pressure, and volume of exhaust associated with going FI will destroy your OEM cats.. but there are plenty of HFC options for factory turbo charged cars. I have read on Subaru forums of folks having good success with some of the magnaflow universal cats... I would probably start by getting a cheap or second hand pair of test pipes and having a shop weld in a couple of those.. they aren't terribly expensive... I considered the same when I thought about keeping cats.. but I have test pipes now and am perfectly happy with them.
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