Dan R Posted July 7, 2021 Share Posted July 7, 2021 Bit of a daft/naive question about a cat bypass for my R500D, what are the pros and cons of the bypass, and once completed what happens to the sensor that was attached to the cat? Link to comment Share on other sites More sharing options...
John Vine Posted July 7, 2021 Share Posted July 7, 2021 I fitted one to my R400D some time ago. IME, it had very little effect on performance, but did make the exhaust note harder. My main reason for fitting it was to spare the cat from unburnt fuel (pops and bangs -- I have rollerbarrels). The oxygen sensor simply transfers to an identical boss in the decat pipe.JV Link to comment Share on other sites More sharing options...
ScottR400D Posted July 7, 2021 Share Posted July 7, 2021 Ditto. JV could have been me writing. Link to comment Share on other sites More sharing options...
ScottR400D Posted July 7, 2021 Share Posted July 7, 2021 One thing. I've always wondered if it would pass MOT without a cat. I always swap mine back for the MOT. A club member pal is having some work done by Premier Power, including a decat pipe and they've told him it will be fine for the MOT. Does anyone agree? Link to comment Share on other sites More sharing options...
David_Long Posted July 7, 2021 Share Posted July 7, 2021 I did some back to back dyno runs with and without, the cat. You may gain torque very low in the rpm, but peak power is better with the CAT. It has a motorsport specification core and not much resistance to flow and it has been well placed to provide a step change in the diameter that helps tune the exhaust. Link to comment Share on other sites More sharing options...
Dan R Posted July 7, 2021 Author Share Posted July 7, 2021 Thanks everyone, ... presumably it really is as simple as unbolt the existing and straight swap for the replacement? or are there some knacks and tricks to doing it nice and simply? Link to comment Share on other sites More sharing options...
Leadership Team Shortshift Posted July 7, 2021 Leadership Team Share Posted July 7, 2021 Perhaps the main benefit is aesthetics...? Followed by weight reduction, of course! James Link to comment Share on other sites More sharing options...
Grant_7 Posted July 8, 2021 Share Posted July 8, 2021 The de-cat pipe is a good 2kg lighter than the catalyst. Link to comment Share on other sites More sharing options...
John Vine Posted July 8, 2021 Share Posted July 8, 2021 Re #4: I don't think a car post-SVA/IVA (that is, one where a cat is required) would stand any chance of passing the MOT emissions test without a cat. The tester will (or should) follow the prescribed flowchart in the MOT Manual.Re #6: Yes, it's really that simple (provided you can undo the sensor). You might want to consider a sealant for the collector branches.JV Link to comment Share on other sites More sharing options...
ScottR400D Posted July 8, 2021 Share Posted July 8, 2021 "Re #4: I don't think a car post-SVA/IVA (that is, one where a cat is required) would stand any chance of passing the MOT emissions test without a cat. The tester will (or should) follow the prescribed flowchart in the MOT Manual"That's what I would think. I'll stick to swapping them over. Link to comment Share on other sites More sharing options...
Phillip Meyer Posted July 9, 2021 Share Posted July 9, 2021 Hmm, surely our cars are bad enough for the environment without making matters worse by removing the cat? Link to comment Share on other sites More sharing options...
7 wonders of the world Posted July 9, 2021 Share Posted July 9, 2021 Cat's are hardly eco friendly...... bearing in mind the extra fuel they demand in order to function.... not to mention mining for the precious metals..... Link to comment Share on other sites More sharing options...
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