Paul372 Posted November 4, 2012 Share Posted November 4, 2012 Hi, i'm looking at buying 1st and 2nd decats for my jap spec tt supe, that's all i need to go bpu but i don't know whats the best size decats to go for 2.5inch or 3inch, the supe has blitz nur spec r exhaust thanks Quote Link to comment Share on other sites More sharing options...
letmeshowyou Posted November 4, 2012 Share Posted November 4, 2012 I personally got on fine with Whifbitz ones on my old car (I think they're 2.5): it made good power, and am intending to do the same on this one. Personally I'm a little concerned that going to 3" would be a little too loud for my liking. Never actually tested that theory though! Quote Link to comment Share on other sites More sharing options...
Noz Posted November 4, 2012 Share Posted November 4, 2012 performance wise you probably wont notice much difference, as a huge amount of back pressure will be limited by the smallest part because of the bottle neck effect, so have a 2.5" system it won't matter if you have a 2.5 or 3" decat. noise will be the biggest factor changed. if you want more noise for 3". Quote Link to comment Share on other sites More sharing options...
johnny g Posted November 4, 2012 Share Posted November 4, 2012 I had Chris Wilson 2.5". They were great, as you'd expect from Chris. Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 4, 2012 Share Posted November 4, 2012 Surely how loud it is depends whats after the de cats, mine are 3" with 95 mm Superdrager exhaust and it's not very loud at all Quote Link to comment Share on other sites More sharing options...
Noz Posted November 4, 2012 Share Posted November 4, 2012 yes obviously exhaust system will be most important factor, but if using the same exhaust system and comparing 2.5 or 3" decats, the 3" will make the same system louder. if you put 2.5" decats on your drager system it would probably make it quieter wouldnt it? Quote Link to comment Share on other sites More sharing options...
mellonman Posted November 4, 2012 Share Posted November 4, 2012 i would bet that the flow of a 2.5" to a restrictor ring would be better then a 3" to a RR as it would be like hitting a wall half way down the down pipe. Quote Link to comment Share on other sites More sharing options...
Dnk Posted November 4, 2012 Share Posted November 4, 2012 yes obviously exhaust system will be most important factor, but if using the same exhaust system and comparing 2.5 or 3" decats, the 3" will make the same system louder. if you put 2.5" decats on your drager system it would probably make it quieter wouldnt it? I don't know what the difference would be if any, isn't the difference in sound level really from removing the cats rather than whether it's 2.5" or 3" ? Quote Link to comment Share on other sites More sharing options...
dan294 Posted November 4, 2012 Share Posted November 4, 2012 I'm on double 3" decats with a nur spec r. It is reasonably loud, not overly so though. I agree with everyone else though. Don't think it would make a massive difference. Sounds good though! Quote Link to comment Share on other sites More sharing options...
Kirk Posted November 4, 2012 Share Posted November 4, 2012 Speaking of sound I actually forgot to mention to get a proper fitting kit for your BOV! Quote Link to comment Share on other sites More sharing options...
SteveC Posted November 4, 2012 Share Posted November 4, 2012 If a restrictor ring is being used on a J-Spec, then I can't imagine there's much, if anything at all, to be gained by using 3" decat pipes over 2.5". Re. noise, I use 3" decats with a Tanabe Medalion Touring system and its hardly any louder than the stock system - it just sounds deeper. Quote Link to comment Share on other sites More sharing options...
mellonman Posted November 4, 2012 Share Posted November 4, 2012 also i would expect a 2.5 too a 3" to be louder then a 3" straight through, my thinking is its like a trumpit that way going smaller to larger just like a mega phone its also proven in the exhuast db register http://mkivsupra.net/vbb/showthread.php?217156-Exhaust-dB-register&highlight=exhaust notice how the 3" decats are louder then the 4" decats with a 4" exhuast Quote Link to comment Share on other sites More sharing options...
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