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05-17-2009, 04:46 PM | #1 |
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High Flow cat pipe questions
It's that time of season again, the mod bug is attacking I do a little bit of modding every summer, and this summer I'm thinking of doing something about my restrictive catpipe and getting some struts. I already have STi springs and I opened the muffler and gutted it last summer, as well as made Williaty's intake and new plugs
Anyways, to start off, are the only 2 companies making high flow cats Stromung and Random Tech? If so, is Random tech really worth the extra $200 premium over Stromung? Also, would it be difficult to make your own catpipe assuming you had these tools at your disposal: Mandril bender, Welder and appropriate piping? There is an exhaust shop not 4 minutes from my house, but I'm cheap and the old man has an industrial welder and access to a mandril bender. If I got my hands on an appropriate High Flow Cat, think I could mod me up a custom cat? Or is it a bad idea? As for the high flow cat, if I got one that was correct diameter and made for....let's say a 200 HP car in stock trim, would that suffice? I'm going off of the thought 'More HP means more air' so the flow would be good I assume? Thanks for any ideas
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05-17-2009, 05:10 PM | #2 | |
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I would search for more info on this because I think the stock cat(s) is not a restriction unless you have significantly increased the flow rate of the engine via cams, etc. I could be thinking of the muffler, though. Also, magnaflow and dynomax make generic HFC's that you could fab up a piece with, too. I'm sure there are more companies too |
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05-17-2009, 05:28 PM | #3 | |||
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05-17-2009, 06:24 PM | #4 |
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random tech and stromung are the only "bolt-on" cats out there. i would save the money and do the cat and header together. if u get the random tech one, u probably won't throw a CEL, where the stromung is more likely to b/c it is only 1 cat. this is the easier, more expensive way.
if u do "frankenstein" it, u need a 2.25" inlet and outlet diameter and 2 cats to not throw a CEL. then u have to have the shop bend the pipes in the right way and add flanges so it will bolt up to the stock header. this is the harder, cheaper way. i did the "bolt-on" way, although more expensive. the sound is sick, especially if u have a catback on the car. mine is the stromung single tip and definitely recommend it if u don't have a CBE yet. |
05-17-2009, 07:10 PM | #5 | ||
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05-17-2009, 08:58 PM | #6 |
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if your concerned about smog test, if you have one you likely wont pass. As the extra flow prevents it.
If no smog then do what you like. |
05-17-2009, 09:58 PM | #7 | |
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I was hoping both cats would be on the catpipe, because then I could swap out before I would go for an inspection, but if I need to mess with the UEL headers to make a high flow system work, I'm not sure if I will go through with it. UEL will cost more and I'll have the same flow as the EL stockers. PS - Cant find crap on stock 2.5i CFM anywhere. |
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05-17-2009, 10:11 PM | #8 |
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Here's a thread by williaty which includes his conclusions regarding track pipes and HFCs on a stock engine.
http://forums.nasioc.com/forums/show....php?t=1698802 |
05-18-2009, 06:43 AM | #9 | |||||
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Using this formula, and the stock hp rating of my engine, it is this: 173hp (crank) x 1.45cfm = 250.85 CFM. So, in conclusion, not knowing if the first quote above applies to all Subaru Cats or just 2.5RS cats, the stock set up is at it's limits just at stock form. I'm no physicist, so I'm sure there are far more variables, but if you want to start getting some numbers above stock form, a cat is not as bad an idea as it may seem. Not disproving Williaty at all because he knows about 500 times more than I do about these engines, but if I'm paper racing it seems there is some leniency to the cat debate. I'll probably edit this shortly with head flow benches because this post is big enough already and my computer likes to randomly refresh pages, thus losing posts EDIT#2: I cannot find flow specs for the 2.5i heads. They may be the same as older models, but I'd like to know, and for sure. It may very well be the heads flow less than the exhaust at this time, and I'd need to know so i can adjust my mods appropriately. EDIT#3: Hell, I can't even find a peak CFM for our stock exhaust systems, but I found that 2.25" STRAIGHT PIPE is 490cfm. Last edited by ScubaruImpreza05; 05-18-2009 at 07:51 AM. |
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05-18-2009, 07:02 PM | #10 |
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Really though, I think hfc are a waste of money.
Expensive HP with the risk of a P0420 code. |
05-19-2009, 07:21 PM | #11 |
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I did some comparing and if the heads are maxed at 250 CF/M, then the system is flowing at it's max because you need that to hit 173 HP crank atleast. So it isn't worth the HFC until you have atleast headwork and/or cams. I R
On the bright side, now I'm getting Tokico D-specs |
05-19-2009, 08:33 PM | #12 |
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^ Money well spent. What springs you gonna get for em? Some STI takeoffs?
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05-19-2009, 09:30 PM | #13 |
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Already have the USDM STi springs on. My stock shocks are starting to bounce more, I was planning on new shocks by 75k miles anyhow
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05-19-2009, 09:36 PM | #14 |
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I would not worry about flow on any aftermarket cat. I would worry if the cat will heat up enough for your O2 sensor to work properly.
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05-20-2009, 02:23 PM | #15 |
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racefacefx... when i said bolt-on i meant that there was no cutting or welding needed. do u have the borla with random tech cat? where is ur answer based?
on a 2006, the header and cats are one unit now, where the older ones, the header and cats were seperate. u need these to be changed at the same time. the dual converter on the random will most likely not throw a CEL. my car didn't throw one with the header. the stromung cat will throw the CEL. if a TWE EL header is added to either, there will be CEL all the time. |
05-20-2009, 02:42 PM | #16 |
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Even better news, I bought rims
(P.S. - what outback said. If it was just a separate pipe with the cats on the stock setup it'd be alot easier...and cheaper, but unfortunately it is not so.) |
05-20-2009, 03:48 PM | #17 | |
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My car threw the P0420 code with stock configuration, and Subaru replaced the catalytic converter under emission system warrantee. This happened with about 65k-70k miles on the odometer. I also requested new O2 sensors with the cat replacment - but I had to foot the bill for these; couldn't get them covered under the warrantee bill. I got the new cat, then bought a Borla header and Stromung CBE. Got the Borla coated - with ceramic-type stuff - hoping to keep the heat in the exhaust and avoid the CEL-P0420. Removed the entire system, then added the new pipes and kept the new OEM cat in service as well. The new exhaust worked great for about 10k miles, then I got another P0420 code. The current code/CEL has come and gone (many times) over several hundred miles, and now has been off for a couple thousand miles. I haven't checked to see if the code is still stored, but I fully expect it to be there, and I also expect that it will return - eventually - after clearing. It seems that the OEM design won't last without killing either the converter or the O2 sensors, at least with my car. Why shouldn't I now go ahead and try a high flow converter - can't be any more problematic than keeping the stock exhaust system? Related question - does the rich-running nature of these cars cause any problem with catalytic converters? Can the excess fuel (with periodic afterfire) destroy the element? If so, then it's likely to happen with a HFC also - right? Does that make the track pipe a longer-lived solution? Thanks, John |
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05-20-2009, 05:41 PM | #18 |
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A track(test) pipe has NO catalytic converter, a high flow does. Unless you mean a HFC that's referred to as a track pipe?. So, you'd have the code always, but nothing would break
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05-20-2009, 05:55 PM | #19 | |
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So a more efficient header design that gets much more heat to the cat will cause the cats to be less efficient and throw a code but an inefficient header, will not throw a code? That doesn't make any sense. There will still be a P0420 code even with factory headers and a HFC. the headers have nothing to do with it. The fact that you havn't gotten a code floors me. |
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05-20-2009, 06:53 PM | #20 | |
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Running rich will melt the cats eventually. I also read a related issue of people's cats melting because of untuned BOVs. OBX has resonated test pipes, and your exhaust will be loud and raspy still. |
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05-20-2009, 10:41 PM | #21 |
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raceface.."So a more efficient header design that gets much more heat to the cat will cause the cats to be less efficient and throw a code but an inefficient header, will not throw a code? That doesn't make any sense." i got lost.
the random tech dual cat was designed not to have a CEL. there is a very rare chance that one will come on. |
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