Guest Suprafly Posted July 25, 2007 Share Posted July 25, 2007 Right, I have recently fitted an aftermarket 3" stainless exhaust, this was a catback, then I bought a HKS cat pipe whilst at JAE which I have now fitted, this cat replacement pipe is also 3" and goes from the flange after the first cat and takes out the second. I am now thinking about taking out cat one which would make it a full 3" straight through system from the turbo elbow back, but... ...I have been told that to totally decat the supe the turbo's are going to run erratically, and that there should be some sort of restriction in the pipe, is this true? To me this sounded like bollocks, what do you guys reckon? Quote Link to comment Share on other sites More sharing options...
mr lover Posted July 25, 2007 Share Posted July 25, 2007 Not bollocks you will need a restrictor ring to stop overboosting Quote Link to comment Share on other sites More sharing options...
markssupra Posted July 25, 2007 Share Posted July 25, 2007 Completely decatting will increase your boost which is why you need a restrictor ring, doing this will also raise other issues. Quote Link to comment Share on other sites More sharing options...
Guest Suprafly Posted July 25, 2007 Share Posted July 25, 2007 Ah right, So I'm assuming this restrictor ring goes between the flanges of the turbo elbow and the pipe with a smaller hole in it to increase back pressure? I'm sure the car was running 11psi max boost before cat two came out, now it's running a consistant 13psi. Is it really worth taking out cat one? I can imagine a sound difference but is there much more of a gain in power? Also what other issues will this raise? Quote Link to comment Share on other sites More sharing options...
robin Posted July 25, 2007 Share Posted July 25, 2007 I think the first cat is more restrictive then the second. With both of them out most J specs will boost too high. Did you find it was much louder when you took out the second cat? Quote Link to comment Share on other sites More sharing options...
Guest Suprafly Posted July 25, 2007 Share Posted July 25, 2007 Definately, but a refined kinda louder if you catch my drift. It's got a nice howl on boost, and a nice low burble on idle. Liking it. Quote Link to comment Share on other sites More sharing options...
markssupra Posted July 25, 2007 Share Posted July 25, 2007 I think stock boost is about 12 psi. Increasing boost will give a noticeable power increase but at the risk of shorter turbo life. Read this link about decatting. Quote Link to comment Share on other sites More sharing options...
hadyn Posted July 25, 2007 Share Posted July 25, 2007 Hello mate. I also have just a catback on my TT at the mo and Im thinking of putting on just a 2nd decat soon. Are you running an uprated fuel pump and plugs with the 2nd cat out? Is there a noticeable gain in power with the 1st cat in? Quote Link to comment Share on other sites More sharing options...
Guest Suprafly Posted July 25, 2007 Share Posted July 25, 2007 Thanks for that mark, I think I'll be leaving cat one in place, according to that link it states that the j-spec fuelling will struggle past 1bar of boost, I'm currently running 13psi and I'm sure 14.4 psi is equal to 1bar I think, so I'm just below, think I'll leave it as is. hadyn... yes a noticable power gain for sure, sounds awesome too, I have no fuelling mods or uprated plugs Read the link about decatting that Markssupra posted. Quote Link to comment Share on other sites More sharing options...
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