Dan_Q Posted April 12, 2013 Share Posted April 12, 2013 its more for the track mate than anything, i don't want to restrict the outings i can do just because of noise. i think most of the venues are 102/105 db but say if i wanted to do an evening at croft i'll be stuck at 88 db!! will be interested to hear what the MOT man says about noise though. from what i've read, plod seems very interested in noise these days too! Link to comment Share on other sites More sharing options...
trebor69 Posted April 12, 2013 Author Share Posted April 12, 2013 Decat turned up today ...... its a lovely piece of steel ......can't wait to fit it Link to comment Share on other sites More sharing options...
monkey76364 Posted April 12, 2013 Share Posted April 12, 2013 Is there much power loss with the double decat on the N/A as that's what worried me. Or would that I ly matter if you went for something like a 3" system to the back box? Link to comment Share on other sites More sharing options...
Graham1984 Posted April 12, 2013 Share Posted April 12, 2013 Is there much power loss with the double decat on the N/A as that's what worried me. Or would that I ly matter if you went for something like a 3" system to the back box? Decats wont give you power loss and at a guess I would imagine NA decats will all be 2.5 inch over 3. If you go double decat on a NA without a twin box catback expect your ears to bleed especially if you get/have a 3inch cat back exhaust. Link to comment Share on other sites More sharing options...
trebor69 Posted April 12, 2013 Author Share Posted April 12, 2013 Decatting the car will increase your power as it is less stifled by the gasses trying to escape, it is a 2.5" pipe as Graham points out .....From what I can gather the 3" system will increase noise level by a couple of db ...... The main thing is the huge increase in noise level from removing both cats . Link to comment Share on other sites More sharing options...
monkey76364 Posted April 12, 2013 Share Posted April 12, 2013 I understand that, it's just I know unlike a turbo an N/A engine does need that back pressure. I had one decat on my old n/a and I thought it was ok sound wise and that was with an RSR back box.... Never did go for both cats out Link to comment Share on other sites More sharing options...
Al Massey Posted April 12, 2013 Share Posted April 12, 2013 I had an autobahn manifold and double decat and it would y'all away from other N/A's but was really stupidly loud Link to comment Share on other sites More sharing options...
Elmo Posted April 12, 2013 Share Posted April 12, 2013 Double de-cat = your neighbours will wish you dead Link to comment Share on other sites More sharing options...
Graham1984 Posted April 12, 2013 Share Posted April 12, 2013 Double de-cat = your neighbours will wish you dead I need to make a video of mine as it's not too noisy at all. Link to comment Share on other sites More sharing options...
trebor69 Posted April 12, 2013 Author Share Posted April 12, 2013 I understand that, it's just I know unlike a turbo an N/A engine does need that back pressure. I had one decat on my old n/a and I thought it was ok sound wise and that was with an RSR back box.... Never did go for both cats out I'll be sticking with a 2.5" bore that will aid the back pressure ......slightly ... Link to comment Share on other sites More sharing options...
Elmo Posted April 13, 2013 Share Posted April 13, 2013 its more for the track mate than anything, i don't want to restrict the outings i can do just because of noise. i think most of the venues are 102/105 db but say if i wanted to do an evening at croft i'll be stuck at 88 db!! will be interested to hear what the MOT man says about noise though. from what i've read, plod seems very interested in noise these days too! Today I had a chat with the guy who owns the MOT test centre, he said their aren't any strict guidlines regards exhaust db, he said the MOT testers use their own discretian, they have to consider if the exhaust is in keeping with the car, if someone has fitted a badboy exhaust to a Corsa then is will most likely fail, however if is a Supra or similar they would probably pass it providing the volume isn't "excessively" loud. Also, with regards to double de-cats, he said they could fail the exhaust on the basis that it is "incomplete", as it deviates too far from the original system fitted at the factory. It makes sense, but I guess different test centres may have different opinions. Link to comment Share on other sites More sharing options...
trebor69 Posted April 21, 2013 Author Share Posted April 21, 2013 Well I fitted my 2nd decat yesterday (Whifbitz) ....still have 1st one on at the mo (but not for long) so I have stainless 2.5" system from 1st cat back and after measuring the db's with "noisewatch" app downloaded on my phone it measures 71 db's at 2k revs, this reading was taken about 12" from tailpipe .......Very happy with the noise level and will be proceeding full steam ahead with the removal of my 1st at the earliest opportunity I understand that this reading is probably not deadly accurate . N/A . Link to comment Share on other sites More sharing options...
Graham1984 Posted April 21, 2013 Share Posted April 21, 2013 Well I fitted my 2nd decat yesterday (Whifbitz) ....still have 1st one on at the mo (but not for long) so I have stainless 2.5" system from 1st cat back and after measuring the db's with "noisewatch" app downloaded on my phone it measures 71 db's at 2k revs, this reading was taken about 12" from tailpipe .......Very happy with the noise level and will be proceeding full steam ahead with the removal of my 1st at the earliest opportunity I understand that this reading is probably not deadly accurate . N/A . Awaiting future noise report Link to comment Share on other sites More sharing options...
Dan_Q Posted April 21, 2013 Share Posted April 21, 2013 Good info on the MOT elmo cheers for posting up That 71 db is low, but at very low rpm- normally when at the track, well, heres how they test it- think i normally get asked to rev it to 4800: Unless stated, all events will have a maximum noise limit of 102db, tested at ¾`s of rpm range at a distance of 0.5m. Link to comment Share on other sites More sharing options...
Elmo Posted April 21, 2013 Share Posted April 21, 2013 Good info on the MOT elmo cheers for posting up That 71 db is low, but at very low rpm- normally when at the track, well, heres how they test it- think i normally get asked to rev it to 4800: 2000rpm is not much more than tick over on cold startup, I'd be interest to know what the db's are at 4800rpm Link to comment Share on other sites More sharing options...
trebor69 Posted April 22, 2013 Author Share Posted April 22, 2013 (edited) Well I took a reading earlier at 4800rpm and it seems that the "noisewatch" app is less effective than I had estimated giving a db reading of , wait for it ....................71 db .......................again !!! Gonna have to get this done properly at some point but not sure where yet ......still sounds the same on tickover as it did before I took the 2nd cat off but sounds crisper on acceleration . I will not be taking my car to any tracks by the way so no noise restriction will apply there . Edited April 22, 2013 by trebor69 (see edit history) Link to comment Share on other sites More sharing options...
Dan_Q Posted April 23, 2013 Share Posted April 23, 2013 how strange! think the levels i've managed were around 79-82 stock IIRC. thanks for trying for us though bud Link to comment Share on other sites More sharing options...
Suprakeith Posted April 23, 2013 Share Posted April 23, 2013 Well the bloke two houses from me asked me if could move car at 5am when start work as it rubbles through his bedroom and i only got 2nd decat at min want 1st decat asap. He wont be happy in winter lol Link to comment Share on other sites More sharing options...
Elmo Posted April 23, 2013 Share Posted April 23, 2013 I can't put into words how loud mine was after I got a 2nd decat. it was rediculous, it sounded like my exhaust had fallen off Link to comment Share on other sites More sharing options...
adarmo Posted April 26, 2013 Share Posted April 26, 2013 I can't put into words how loud mine was after I got a 2nd decat. it was rediculous, it sounded like my exhaust had fallen off I once had an exhaust come apart at the downpipe. People on the pavement ducked as I went past, they thought it was a low flying plane ! Link to comment Share on other sites More sharing options...
Dan_Q Posted April 29, 2013 Share Posted April 29, 2013 LOL! feels horrible doesn' it just to give back to this thread, for the record, both cats installed, single box 2.5" stainless exhaust, 86db. i think i was revving about 4500 rpm. cant remember last years (100% stock) for certain but pretty sure it was around 78db. Link to comment Share on other sites More sharing options...
trebor69 Posted September 30, 2013 Author Share Posted September 30, 2013 (edited) Well I have had both cats off for a couple of months now and although it is very loud (which I kinda like ) the noise that is annoying me is the "farting, blowing" noise under load .....it sounds a little like bumble bee (transformers) but is horrible from inside the cabin .....I presume a double box on the back cuts this out ??? I am considering putting my second cat back on just to see if it stops the farting Its definately not blowing from anywhere either . Edited September 30, 2013 by trebor69 (see edit history) Link to comment Share on other sites More sharing options...
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