CtrMint Posted October 11, 2020 Share Posted October 11, 2020 Hi,Anyone that might be interested in removing their Duratec cat, my blog post is now available including part number etc. It's pitched as usual at the lesser competent mechanics. Hope it helps.https://www.caterham7diaries.com/post/caterham-7-420r-decat-installMark. Link to comment Share on other sites More sharing options...
BobM Posted October 11, 2020 Share Posted October 11, 2020 That looks a very sensible move Mark. I think the main reason I plan to spec a normal side exit exhaust if/when I order a 420R is to keep the separate cat and silencer. The trackday version comes with the cat contained within the main silencer and I'm sure the cat is doomed to failure with the replacement unit being >£1,000.It would also be easy enough to replace that cat section with a small additional silencer which could help keep the noise down for the picky tracks (Donington, Combe, Bedford). Link to comment Share on other sites More sharing options...
CtrMint Posted October 11, 2020 Author Share Posted October 11, 2020 OMG what a difference. Been out for three hours. 2nd gear over run is amazing! The bark is so much fun. I am so impressed it sounds like a monster now. I know RBTB would make it better, but for the time being it's enough, more than enough. Link to comment Share on other sites More sharing options...
Area Representative Piers300 Posted October 11, 2020 Area Representative Share Posted October 11, 2020 Very well done and good to watch. Link to comment Share on other sites More sharing options...
John Vine Posted October 12, 2020 Share Posted October 12, 2020 Spinning the cat* to remove the lambda sensor is a good tip. That's exactly how I do mine.(* No felines were hurt in this procedure.)JV Link to comment Share on other sites More sharing options...
R400svn Posted October 12, 2020 Share Posted October 12, 2020 I currently have the trackday exhaust on a 420r with RBTB and it sounds ok and does keep the overall sound down but for me its a little disappointing in noise when your out for a blast. I have a standard silencer arriving tommorow to swap over so will see how that goes or if it will be to loud and annoying. Be also interesting if it restrict power. Link to comment Share on other sites More sharing options...
Mrp Posted October 12, 2020 Share Posted October 12, 2020 If you have decat, side exhaust and RBTB you will good sounds and flamesMrp Link to comment Share on other sites More sharing options...
Mrp Posted October 12, 2020 Share Posted October 12, 2020 When I had the rear end damage repaired by Caterham on my new 420R I also got them to do the cat pipe and RBTB. when it was back I took my wife out in it she said "it didn't sound like that before that woman hit it has that caused the change". Mrp Link to comment Share on other sites More sharing options...
Nigel B Posted October 13, 2020 Share Posted October 13, 2020 Haha brilliant! I fitted a decat pipe to my 420R last year. I prefer the more strident raspiness without the cat, but I did notice there's a quite distinct step up in loudness at about 3000rpm that doesn't seem to be there with the cat fitted. With the cat, the increase in loudness happens steadily as the revs climb. Has anyone else noticed that? I still have the cat fitted at the moment, following the MOT. I really should get round to taking it off again... Link to comment Share on other sites More sharing options...
ScottR400D Posted October 13, 2020 Share Posted October 13, 2020 To be honest Nigel, I didn’t notice much difference at all when I fitted mine...... Link to comment Share on other sites More sharing options...
CtrMint Posted October 13, 2020 Author Share Posted October 13, 2020 Mine is definitely louder, or may be I was just being more provocative with the loud pedal... Link to comment Share on other sites More sharing options...
Nigel B Posted October 13, 2020 Share Posted October 13, 2020 Perhaps it's just me then? Strange. Peter, it must be the growl from your roller barrels, drowning out the exhaust noise! Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted October 13, 2020 Share Posted October 13, 2020 With the standard re-packable R400D silencer filled with Acousta-fil and no cat, I need earplugs all the time, Also, I can't pass noise regs set to <93dB at 15 metres at certain events I attend, without an additional SuperTrapp exhaust silencer over the end of the tail pipe that I can fit or remove in a couple of minutes. The car does sound good and revs very freely with the catless exhaust config, though. Link to comment Share on other sites More sharing options...
R400svn Posted October 13, 2020 Share Posted October 13, 2020 Well just removed track day exhaust frrom the 420 and put a side exit on and what a difference. Much better noise, nice flames and if say it feels quicker or certainly freer reving. Just the length of the trackday exhaust must cause some restriction Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted October 14, 2020 Share Posted October 14, 2020 For noise reduction on the track, those of us at the events I go to that are above the noise limits have elected to use either a removable or semi-permanent solution using SuperTrapp or similar discs.My R400D requires 18 discs to give 5 to 6dB of attenuation, but also have a greater exit cross section between the disc pack than the pipe diameter itself, to eliminate any appreciable power loss.My homemade device weights only half a kilo (including cone deflector and shield to prevent damage to the rear wing from hot exhaust that exits at 90 degrees to the normal flow). It uses 4 Allen bolts on the back to clamp two half-moon sections behind the rolled exhaust tip lip. Most people just have the SuperTrapp adapter either clamped with an exhaust clamp or welded on to the exhaust tip, removing the discs when not needed. Much lighter and cheaper solution than an add-on rear exhaust addition: Link to comment Share on other sites More sharing options...
CtrMint Posted October 14, 2020 Author Share Posted October 14, 2020 I wonder if that would work on the 620R, letting me replace the rear exit for a side exit and also pass noise regs? Link to comment Share on other sites More sharing options...
7 wonders of the world Posted October 14, 2020 Share Posted October 14, 2020 Although the supertraps are effective as regards noise they do affect the power, we did test on the rollers many years back. Link to comment Share on other sites More sharing options...
Alan.gilford Posted October 14, 2020 Share Posted October 14, 2020 Hi R400svn, what was the part number for the silencer you fitted ? I have the rear exit exhaust and RBTB on a 420r. Just wanted to check the length is the same with the rear exit collector pipe.Thanks Alan. Link to comment Share on other sites More sharing options...
R400svn Posted October 14, 2020 Share Posted October 14, 2020 Hi Alan. I have an Sv but dont think the silencers are different but maybe the collector pipe might be. i purchased the polished 7 inch silencer re.380X0006Ai just looked at a couple of side picks of standard cars with the normal cats and the pipes a pretty similar length. I did notice when fitting it does not sit over the collector pipe quite as far as the old silencer but enough all the same. well worth changing over Sounds so much better. Only thing for me is i lime the look with the rear silencer. Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted October 14, 2020 Share Posted October 14, 2020 Although the supertraps are effective as regards noise they do affect the power, we did test on the rollers many years back.It depends on the tradeoff of number of plates vs noise reduction.With the standard 12 plates with the 2.5" SuperTrapp the power loss is noticeable on the R400D, feels like about 15% or so, but not measured accurately. I would estimate 6 to 7dB noise reduction, but not measured with the standard noise gear at the events. With 18 plates I'm loosing less than 2km/h at 160km/h on the track on a short straight with a 70km/h entry, which would equate to about 2% power loss / 4bhp. WIth 18 plates I dropped from just over 93dB to 88dB at 15 metres on the same day and same autocross course where I had to be under 93dB after receiving a warning.With 12 plates the cross section of the gaps in the entry to the plates (0.5mm thick plates with 1mm gap between them) is 77% of the exhaust cross-sectional area, with 18 plates it is 116% of the area. I think 24 plates would be the maximum that would be possible to use, for 155% of the exhaust cross-sectional area and perhaps about 4dB of noise reduction. Link to comment Share on other sites More sharing options...
Leadership Team Shortshift Posted October 15, 2020 Leadership Team Share Posted October 15, 2020 Replying to #16"I wonder if that would work on the 620R, letting me replace the rear exit for a side exit and also pass noise regs?"Mark - I'd be confident that a Raceco would work well on your 620R. I've got them on both my R500 and CSR and they are very effective. And lightweight. And look cool...James Link to comment Share on other sites More sharing options...
Nigel B Posted October 15, 2020 Share Posted October 15, 2020 Prompted by this thread, I refitted my decat pipe yesterday after a couple of months running with the cat, as I hadn't got round to removing it again after the MOT. Strangely enough, the issue I had with a sudden step up in loudness at 3000-ish rpm has completely gone! I can't understand what has happened there. Perhaps it has mellowed with use? Odd. Link to comment Share on other sites More sharing options...
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