highish exhaust backpressure but cat looks fine - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-04-2008, 01:46 AM   #1
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Default highish exhaust backpressure but cat looks fine

Setup: GT2560, ETD manifold, TDR i/c, custom BEGI divorced downpipe
exhaust: 2.5" custom, 2.5" Maremont 200-cell metal cat, 16" resonator, 5x8x22" Magnaflow muffler.

The cat rattles a bit when I pound its body. I disconnected the downpipe, shone a light, and peeked at the brick with a mirror. The brick looks OK; it's brown, not broken up, and doesn't look clogged. I poked at it with a jack handle and the brick is slightly loose in the casing, but the brick seems whole.

So with 10 psi of turbo boost, data is below. I used to get 4-4.5 psi at 6500 RPM. (Admittedly that was with the car making less power due to a smaller turbo).

4000 2.5
4500 3
5000 3.75
5500 4.5
6000 5.25
6500 6
7000 6.75
7250 7.5

If I could get 4.5 psi at 6500 RPM with a new cat, well, 1.5 psi seems like not a huge amount ...

Thoughts?
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Old 10-04-2008, 01:57 AM   #2
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Jason, do you have to run a cat?
If not I would just delete it.

If you do have to use the cat, what do you use the car for? Daily, track?

I just ask because that difference in boost may or may not be worth your effort.

Last edited by TURNS101; 10-04-2008 at 03:01 PM.
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Old 10-04-2008, 10:18 AM   #3
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maybe there's some sort of resonance in the rattly core at high gas flows that causes extra turbulence as it wobbles back and forth.

maybe high time to try one of those spun metal cats the kids all like.
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Old 10-04-2008, 12:13 PM   #4
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You're still running 8 psi? I thought you built your engine up?
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Old 10-04-2008, 12:31 PM   #5
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if the brick is loose, then the cat is not fine

if you must have a cat, get a 100 cell metal core one
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Old 10-04-2008, 03:00 PM   #6
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Y8s makes alot of sense.

With that moving around it may def be making the exhaust flow less efficient.
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Old 10-05-2008, 12:55 AM   #7
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y8s, it IS a metal cat. I'm an early adopter. In my OP I wrote 200-cell Maremont metal cat. I installed it before Magnaflow came up with theirs. Or is a "spun metal" cat something newer?

Would oil burning cause the brick to go loose? I thought oil burning would clog some of the "pores". (I didn't see any).

Zabac, 100-cell? I thought the lowest was 200-cell? (what I have)

Turns101, car is a DD. I also like a quiet exhaust. And I enjoy breathing clean air...

JimFSU, I've been running 10 psi for the longest time. You may be confusing me with someone else. I do plan to dyno tune it and see if I can run an efficient 12 or 14 psi.
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Old 10-05-2008, 11:23 PM   #8
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LOL is there a resonator that looks like a cat from the outside and is quiet?
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Old 10-06-2008, 07:59 PM   #9
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magnaflow has some
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Old 10-07-2008, 02:41 AM   #10
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.. that looks like a cat??
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Old 10-07-2008, 03:09 AM   #11
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Why not
1) take a dead cat from a junkyard car or from behind a muffler shop
2) drill out a 3.0x diameter hole in the center or just bash out the innards with a hammer and chisel)
3) place a 3" diameter pipe through the center,
4) weld it in place
5) grind the welds to hide, paint as necessary to look correct
6) install in vehicle for great justice
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Old 10-07-2008, 03:11 AM   #12
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Alternatively,
1) saw old cat in half.
2) Weld outer shell around test pipe.
3) install in vehicle

I suspect it is illegal to sell things that imitate the appearance of a cat without being one.
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Old 10-07-2008, 03:57 AM   #13
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Quote:
Originally Posted by JimAtFSU View Post
I suspect it is illegal to sell things that imitate the appearance of a cat without being one.
You sir, have never been on eBay


http://cgi.ebay.com/ebaymotors/90-93...mZ380068444031




http://cgi.ebay.com/ebaymotors/Mazda...mZ250304628430

There are several more.
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Old 10-07-2008, 03:17 PM   #14
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http://www.siliconeintakes.com/produ...7d0875e6dae1f2

Not any quieter than any other test pipe though.

If you're looking for a cheap metallic cat for testing:

http://performance-curve.com/index.a...&Category=1414

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