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2000 2.5RS
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185 Posts
Discussion Starter · #1 ·
Hey guys, I got a CEL for my cat and now i'm shopping for a high flow cat. I'm planning to buy one off ebay, probably some cheap magnaflow hfc. Can someone tell me if this universal one would fit? Any other brands you would suggest? Thanks!

Pipe Inlet Size: 2.25"
Pipe Outlet Size: 2.25"
Overall Length: 13"
Tall: 4"
Width: 6.5"
 

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6,423 Posts
if you went full 2.25 exhaust it would.
just welding it into stock exhaust defeats the purpose.
 

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2003 BMW 325xi
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528 Posts
i have the spun case one on my car.....i have 2.25" DIY header back exhaust.... i would definitely reccomend the spun case, because shit gets real tight under there when trying to go full 2.25"
 

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Premium Member
'17 Impreza Sport, '15 OB 3.6R
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9,806 Posts
FWIW you'll probably have a CEL when you put that in, too. :)

P0420.......... search the forum, there's a million topics about it. The only fix, that doesn't always work, is a rear O2 bung extender unit. Such as:

http://www.rallitek.com/rao2sesp.html
 

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Premium Member
'17 Impreza Sport, '15 OB 3.6R
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9,806 Posts
Doesn't work the same for all cars. For some people, it prolongs the time between CELs. Some get rid of it entirely.
 

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2002 Forester
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464 Posts
+1 for spun cats, very compact design, incredibly easy to fit. They just don't have built in O2 bungs, so the shop will simply have to weld them in. (not hard for them) Look for part number 5996x on Ebay, x corresponding to inlet-outlet size: 3, 4, 5, etc...

I'll note for flow rates, our engines push up to around 300cfm at redline. A normal pipe will support up to 115cfm/sq.in. before being considered overly restrictive, i.e. velocity gains start to become outweighed by flow restriction. If you work this out, you will notice a 2" pipe will fully support the flow levels our engines can create. Stepping to a larger size pipe only lowers flow speeds which reduces the effect of scavenging. (read "not helpful")

The side question is where are the biggest restrictions? Well, that's the cats and muffler, depending on what you pick. If you step to a 2" pipe and start using 2" in-out cats and mufflers, you need to pick more carefully and buy only ones that flow very well. If you step to a larger 2.25" size, more cat and muffler choices will support the same flow levels. By 2.5", pretty much anything would work, but you're already cutting down on flow speeds. Most will run 2.25" all the way back. This is what the OBX and TWE headers exit as, and you don't have much for concerns over cat and muffler choices as long as you buy some form of high flow cat and some form of straight through muffler design.
 

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'99 Hybrid RS Coupe
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2,719 Posts
I'm running a 2.5" magnaflow cat in my 2.25" exhaust with cobb EL headers.
 
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