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Old 16th November 2008, 16:43   #1
RussCan
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Secondary Cat Removal ?'s
Hey guys, I'm new here to the forum and as you can see this is my first post. I will be getting some pictures up soon of my car. I plan to start modding soon and wanted to know if there is a clear consensus on HP/TQ gains if any by removing the secondary cats alone or should I add it to the list of mods to do. I've searched and found some info but it was unclear if there were gains with the cat delete alone.

All the Best, Russ
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Old 17th November 2008, 03:08   #2
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I believe there is a dyno showing some gains in the mid rpm range.
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Old 17th November 2008, 03:55   #3
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i've heard little to no gains, and also from what i've heard you dont want to remove the resonator as it acts as an X-pipe
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Old 17th November 2008, 06:02   #4
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RussCan your M5 looks great. Post more pics. The Rad 10 wheels look good.
There is no power loss with the secondary cat delete.
There is also known hp gains from primary cat delete. For this you can do aftermarket headers (Supersprint, Evosport or RDSport). There is also the RPI header design which is the same OEM exhaust manifolds with the primary cats removed and reconnected to the rest of the exhaust system.
The power gains is from the primary cat removal and that's the bottomline.

Good luck with the mods and post more pics of your beautiful M5.

Ranger
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Old 17th November 2008, 07:42   #5
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Welcome Russ! RPI has various options for you going from headers to Sect 1-3 (ST or GT) depending on your preference.

As Ranger said, the major power gains comes from the removal of the primary cats (check out RPI GT Headers +28whp). In addition, recently RPI GT Sect 1 revealed an estimated gain of 7-8whp; check it out: #18
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Old 18th November 2008, 04:25   #6
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RussCan, if you are going to mod, you should look and hear the full exhaust. I have the ASR Gen II and love it. Where in NC are you?
Sam - in Raleigh
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Old 18th November 2008, 05:33   #7
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It inconclusive whether by removing 2nd cats alone from stock setup gain power. Sometime it depends on the rest of the system for overall dynamic flow. Here is one example, Dixis Titanium Exhaust and H Pipe (post#32).

I know that full RPI system with hi-flow cats VS straight pipe on section1 could pick up as much as 8rwhp.
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Old 18th November 2008, 08:32   #8
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Based on my experience, you may experience loss in torque having PRIMARY cat, SECONDARY cat and Resonator ALL removed. I don't think you will loose power/torque just removing the Secondary cat.
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Old 18th November 2008, 08:45   #9
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get rid of it! i don't regret itttt at all!... sounds better tooooo
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