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Old 08-27-2016, 07:53 AM   #1
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Default What to expect after removing catalytic converter?

Gents,

I needed to pull the header to get it welded--the EGR tube fitting cracked. While I had it out, I decided to inspect the cat. The metal spiral core had separated from the case and was fairly loose inside. I had the core removed and I've remounted the empty cat. I drove it a short distance to work--I wanted to make sure the header welding was okay. AFRs seemed fine around town, so I took it on the highway on the way home. Nothing out of the ordinary.

Is there anything I should expect, like lower boost levels, from running without the cat? Do I need a retune for track use? Should I just get another hi-flow cat?

Thanks,
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Old 08-27-2016, 10:39 AM   #2
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I wouldn't expect a change in boost level, especially with a blower. Keep an eye on AFR's under acceleration. Reducing exhaust restriction should pick up some power and lean out your tune. You may need to add a little fuel to the top of your VE table.
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Old 08-27-2016, 12:42 PM   #3
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its gonna sound nasty/raspy and stink a little
otherwise no issues.
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Old 08-27-2016, 02:55 PM   #4
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its gonna sound nasty/raspy and stink a little
otherwise no issues.
It sounds stupid. Would I be better off with a new high flow cat or a straight pipe?
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Old 08-27-2016, 03:25 PM   #5
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Expect to save 15% or more by switching to Geico.
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Old 08-27-2016, 03:47 PM   #6
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Originally Posted by poormxdad View Post
It sounds stupid. Would I be better off with a new high flow cat or a straight pipe?
A straight pipe won't meaningfully change the sound relative to the gutted shell you have now. Might be a tiny bit louder (as you'd be removing what is effectively an expansion chamber), but it's definitely not going to improve things.
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Old 08-27-2016, 05:17 PM   #7
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Adding a resonator... or a turbo... will help the rasp a lot.
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Old 08-27-2016, 05:35 PM   #8
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It sounds like a garage door spring being hit by a clown with a maraca.
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Old 08-27-2016, 06:21 PM   #9
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Quote:
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It sounds like a garage door spring being hit by a clown with a maraca.


That just made a little bit of expensive scotch go through my nose. Burns like hell, in case you were wondering.


What does the rest of the exhaust system look like?
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Old 08-27-2016, 07:26 PM   #10
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Quote:
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That just made a little bit of expensive scotch go through my nose.
What were you drinking? I like scotch.
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Old 08-27-2016, 11:57 PM   #11
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What were you drinking? I like scotch.
Balvenie 21yo or GTFO.
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Old 08-28-2016, 09:46 AM   #12
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Sorry, just a 15 year Glenlivet.
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Old 08-28-2016, 11:17 AM   #13
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No love for the Lagavulin 16?
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Old 08-28-2016, 12:17 PM   #14
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Haha good stuff! We are all manly men. We drink scotch and drive silly little cars. We know we are men, we dont need to prove to the world!
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Old 08-28-2016, 10:08 PM   #15
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Quote:
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: What does the rest of the exhaust system look like?
Seems to be in pretty good shape. I got everything from Jason at Enthuzacar. I have the longest Magnaflow resonator that will fit, and a Borla Pro something muffler. If I were to do it again, I'd get a four inch or so shorter resonator and have it welded up so the can was as far away from the back of the seatwell as possible.

Although I'm partial to anything from The Macallan or Laphroaig, I have recently been enjoying Alberta Blended Rye Whisky Dark Batch from Canada. Just a little sweet.
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Old 08-30-2016, 12:44 PM   #16
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No love for the Lagavulin 16?
Oh there is love. Distillers Edition or regular Lagavulin 16 all day.
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Old 08-30-2016, 12:52 PM   #17
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(...) and a Borla Pro something muffler.
Well there's your problem.

Most of the exhaust systems that Enthuza builds use straight-through mufflers, and the Borla Pro is one of those. These mufflers are basically just a huge glasspack- they do not have any internal baffling.

This is ideal for turbocharged engines, since the turbo itself happens to be a very good muffler. But for supercharged or naturally-aspirated engines, they're not much better than an old-school cherry bomb in terms of quieting the high frequencies.
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Old 08-30-2016, 12:56 PM   #18
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Quote:
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Well there's your problem.

Most of the exhaust systems that Enthuza builds use straight-through mufflers, and the Borla Pro is one of those. These mufflers are basically just a huge glasspack- they do not have any internal baffling.

This is ideal for turbocharged engines, since the turbo itself happens to be a very good muffler. But for supercharged or naturally-aspirated engines, they're not much better than an old-school cherry bomb in terms of quieting the high frequencies.
Chambered mufflers are not any better, but also kill flow, so they suck twice as hard.

You want the bestest quietest high flow setup? big maggie with a cat. done

I learned a long time ago that resonators don't quiet down an exhaust. I've gone as far as running 2 21" resonators (think about that for a second), and it still wasn't "quiet". you want a big, thick, (that's what she said) muffler. the bigger in girth, the better (again, what she said)
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Old 08-30-2016, 01:30 PM   #19
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There's a difference between a huge resonator and a baffled muffler.
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Old 08-30-2016, 01:36 PM   #20
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