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Open Headers or Cat?

Old Oct 14, 2021
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Open Headers or Cat?

my cat is kinda ****ed up and very rusty so instead of coughing up money for a new one, could i just instal open headers? been looking around and they’re about the same price. any downsides to open heads?

d17a1
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Old Oct 14, 2021
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Re: Open Headers or Cat?

It'd be unbearably loud, for one. Two, you'd fail inspections depending on where you are. Three, it'll throw an engine light. Four, you'll lose a bunch of bottom end torque due to insufficient back pressure. Did I mention how loud it would be?

Just get a cat.
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Old Oct 14, 2021
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Re: Open Headers or Cat?

Originally Posted by Chezboat24
It'd be unbearably loud, for one. Two, you'd fail inspections depending on where you are. Three, it'll throw an engine light. Four, you'll lose a bunch of bottom end torque due to insufficient back pressure. Did I mention how loud it would be?

Just get a cat.
ight thank you man. i respect your honesty
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Old Oct 14, 2021
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Re: Open Headers or Cat?

I accidentally ran almost open header on my D17A2 (2002 ex coupe MT). When I installed my header, I unknowingly offset the downpipe connection by like.. a quarter inch (don't ask how I managed to do that). It sounded like a harley, was, as mentioned, almost unbearably loud, and I had a metric crap ton of trouble getting up a semi-steep driveway due to the lack of low end torque. I had to rev it up to like 3000-3500 and almost dump the clutch to get it to move up that driveway

now, I notice you're talking about "installing open head"... do you mean a catless exhaust mani? Open header is way different. Open header means you're disconnecting the downpipe/midpipe at the exhaust manifold connection and letting it dump right there. Catless means you have a header that's a cat delete (either a test pipe or straight up exhaust runners going to a singe or 4-2-1 collector) and still allows exhaust gases to run the length of the mid-pipe, through the muffler, and out the tailpipe.
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Old Oct 14, 2021
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Re: Open Headers or Cat?

Originally Posted by xRiCeBoYx
I accidentally ran almost open header on my D17A2 (2002 ex coupe MT). When I installed my header, I unknowingly offset the downpipe connection by like.. a quarter inch (don't ask how I managed to do that). It sounded like a harley, was, as mentioned, almost unbearably loud, and I had a metric crap ton of trouble getting up a semi-steep driveway due to the lack of low end torque. I had to rev it up to like 3000-3500 and almost dump the clutch to get it to move up that driveway

now, I notice you're talking about "installing open head"... do you mean a catless exhaust mani? Open header is way different. Open header means you're disconnecting the downpipe/midpipe at the exhaust manifold connection and letting it dump right there. Catless means you have a header that's a cat delete (either a test pipe or straight up exhaust runners going to a singe or 4-2-1 collector) and still allows exhaust gases to run the length of the mid-pipe, through the muffler, and out the tailpipe.
ohhh shoot, yes i meant a catless downpipe. my bad. i thought those were open headers whoops. i’d still have my muffler and res on there (i’m personally not a fan of super loud cars), it’ll just be one straight pipe instead of my cat, hope that’s makes sense

something like this

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Old Oct 14, 2021
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Re: Open Headers or Cat?

Get a cat, selling the old cat to scrap will give you more than enough to get a replacement
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Old Oct 14, 2021
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Re: Open Headers or Cat?

you can always convert to an EX exhaust setup which would give you access to a **** ton more options. You'd have to buy O2 sensor extension harnesses since the EX cat is located just about under the shifter assembly as opposed to integrated into the exhaust manifold.

(here's a diagram I drew up in case you're unfamiliar with the differences)



As far as I know, the axle back portions are identical. If you decide to go full exhaust, I'd stick to 2.5" piping at the most. 2.25" is ideal. I ran a 2.36" (60mm) b-pipe (A'PEXi World Sport 2 cat-back) with a 2.5" downpipe (Random Technologies high flow catted downpipe -- now defunct, I believe) and that was actually pretty good. That was connected to a Kamikaze (now defunct) ceramic coated header. Got lots of compliments on my exhaust sound
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