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Old 11-16-2005, 01:26 AM   #1
WillysPU
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Default Hi flow cat vs No cat?

Anyone have any performance numbers (or guesses) that would show the amount of improvement gained by having a catless dp vs having one with a high flow cat?

Specifically, I have a vf34, uppipe, headers, sti i/c,helix dp catted dp and a borla hush. I am looking for a bit more torque and was wondering how much of a difference I would feel from a catless dp. So basically swapping out the catted helix for a catless helix.

The car is used at the track often.

Any information or comments welcome.
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Old 11-16-2005, 02:09 AM   #2
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cats will make a 5-10whp difference... dyno dependant blah blah
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Old 11-16-2005, 04:15 AM   #3
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Dump the Cat, you don't NEED it anyway, (it's not like you're breathing the air BEHIND you! unless you own the Ozone layer, (oxides of nitrogen-my favorite!)LOL!).
But seriously, I would say get rid of it if you spend time at the track. I don't run one myself. Never have.....

Cheers

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Old 11-16-2005, 07:33 AM   #4
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I won't make enough difference. Keep and think of the future and the environment
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Old 11-16-2005, 11:40 AM   #5
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Great comments. 2 questions:
1.
Is the smell of a catless exhaust as different (bad) as some people have written? My car lives in the garage and I don't need more spousal harassment.

2.
Are the lengths of the helix catted and catless the same, can I just swap one for the other?


Thanks!
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Old 11-16-2005, 12:10 PM   #6
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the difference in smell is noticable (at least from my experience)

the lengths are the exact same
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Old 11-16-2005, 12:30 PM   #7
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It is noticeable smell from my fiances standpoint. I'm swapping my racepipe for a hi-flow cat tomorrow. I probably won't notice a difference though since I'm losing the TD04 for a VF39 at the same time
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Old 11-16-2005, 12:38 PM   #8
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I can smell a cattless car. It stinks, especially when driving behind one.

If you want to track the car and want to squeeze the last HP out of it, but don't want to stink during the week, check out PDE. At one time they were selling a downpipe with a removable cat and a race pipe. Take out about a dozen bolts and the cat goes in and out.
Not cheap, but might just be the thing for your kind of application.
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Old 11-16-2005, 01:29 PM   #9
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There was once I followed a WRX with a melon shooter muffler... We reached at an open road and he downshifted, WOT, etc....
Poor me that I have my vent setting at fresh air instead of recirculate... and geez, this guy STINKS! It stinks as bad as those vintage 60s/70s muscle car haven't done smog check in the past 30-40 years!

For my case, I have 1 HF cat as the only cat in the exhaust system. It doesn't stink as long as the engine is not idling (coz cat isn't heated enough), but even if it stinks, it only smells like I'm visiting a gas station.
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Old 11-16-2005, 02:34 PM   #10
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I felt no change in power between a catless stock midpipe and a Stromung High flow catted midpipe.
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Old 11-16-2005, 02:48 PM   #11
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Regarding the smell: If you stand behind your car right after starting it when cold, you'll smell the exhaust for for a little bit before the cats warm up. That smell will be present but much worse without any cats all the time.

It's easy to tell if a car is running catless when driving behind it with either the fresh air vents on or the windows down.

I vote for at least a single high flow cat for a daily driver.
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Old 11-16-2005, 02:53 PM   #12
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I switched from a catless Helix to a catted Helix.

I noticed a drop in power, a drop in noise, and a drop in smell.

Stock turbo, no EM, aftermarket headers, UP, muffler.
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Old 11-16-2005, 02:54 PM   #13
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Quote:
Originally Posted by drees
...That smell will be present but much worse without any cats all the time...
Were you saying if a rex has 0 cats in it, it won't stink as bad (or worse) as a rex with at least 1 HF cat?

I'd say a rex with 0 cats is stinky all the time, regardless of the engine is cold or warm; While for a rex with at least 1 HF cat, it stinks when cold started , and perhaps also when warmed but idling engine (<-- my case).
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Old 11-16-2005, 03:44 PM   #14
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Quote:
Originally Posted by dcwrx2
Were you saying if a rex has 0 cats in it, it won't stink as bad (or worse) as a rex with at least 1 HF cat?

I'd say a rex with 0 cats is stinky all the time, regardless of the engine is cold or warm; While for a rex with at least 1 HF cat, it stinks when cold started , and perhaps also when warmed but idling engine (<-- my case).
Nope, you're saying the same thing as me, I just said it in a confusing way.

Cold start w/cats = smell
All the time wo/cats = smell
Idle w/1 highflow cat = may smell?
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Old 11-16-2005, 03:50 PM   #15
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Heh, gotcha~
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Old 11-16-2005, 04:45 PM   #16
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Quote:
Originally Posted by fliz
I switched from a catless Helix to a catted Helix.

I noticed a drop in power, a drop in noise, and a drop in smell.

Stock turbo, no EM, aftermarket headers, UP, muffler.
no em is the biggest thing, reset the ecu and let it learn itself

the only thing your dulling with a catted helix over a catless is throttle response

end of story

<-been back and forth between catted and catless for a while
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Old 11-16-2005, 04:53 PM   #17
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well, your wrx has three of them...get rid of them all and put in a single high-flow in the downpipe (get a TBE). For me, the much-less polluting factor and smog-passing capability was worth the 5whp loss. Also, you should only need a single high-flow to pass CA emissions and any cops that have a grudge...assuming you have EM that can take care of CELs.
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Old 11-16-2005, 04:54 PM   #18
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Great info, as I mentioned in the very first post I have the helix with the high flow cat and I don't really notice any "extra" bad smell at start up or idle. I do have a 56 Willys Pickup truck that smells pretty bad but it needs an engine rebuild.

Maybe I am weird but I actually like the smell of race gas exhaust.

So it sounds like a bit more power, a bit better throttle response and more stink.
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Old 11-16-2005, 04:57 PM   #19
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go catless, its the only way our subies like to be heard!
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Old 11-16-2005, 06:10 PM   #20
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Quote:
Originally Posted by redeemedsoul
go catless, its the only way our subies like to be heard!
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Old 11-16-2005, 06:31 PM   #21
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Can't tell you one way or the other but do have a tid bit of advice if you go with a cat.

Find out if there have been any problems with the brick breaking loose in that DP. And if it does break loose is it covered by any type of warranty.

I was running the TXS high flow cat until the brick broke loose and started rattling. Found out that it was a known problem. TXS's high flow cats are made by Magnaflow and they don't cover that stuff unless the cat cracks. The bricks break loose much more often than they crack. I went catless only b/c the high flow would probably fail again eventually.

So you may want to find out about the failure rate of the Helix catted DP if there's any info. I'm not saying it'll happen but it's just another thing to consider.

Ryan
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Old 11-16-2005, 07:13 PM   #22
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Keep my finger crossed for my MadDad V2 DP (1 HF cat).... Haven't heard of any rattling from the DP since installed.
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Old 11-16-2005, 07:21 PM   #23
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Quote:
Originally Posted by WillysPU
Anyone have any performance numbers (or guesses) that would show the amount of improvement gained by having a catless dp vs having one with a high flow cat?
One of the shows on SpeedChannel did a dyno run comparison on the effects of a cat in the exhaust system. They didn't specify a high flow cat, just a cat. Same car, same dyno, same day. Probably not more than an hour apart, just enough time to make the swap. End result? The cat was worth 5 hp. You will probably get a bigger difference with a high flow muffler over stock.

I have seen high flow cats advertised as flowing more than twice the air than a stock cat. So, you can add that possibility into the equation.

I would keep at least one cat. As others have said, no cat = stinky, usually very stinky. And, having driven someone's WRX w/out cats, it was easily noticable while driving the car. Bad juju.
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Old 11-16-2005, 07:23 PM   #24
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Quote:
Originally Posted by dcwrx2
Haven't heard of any rattling from the DP since installed.
It'll take awhile if it does break loose. My TXS high flow failed near the 15k mark.
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Old 11-16-2005, 07:36 PM   #25
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Mine has 10k miles.... hope it last forever, lol.
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