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post #1 of 11 (permalink) Old 27th May 2020, 22:04 Thread Starter
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What part of the setup on the 86 do i need to change so it passes mot?

It has
catless manifold
Catless front pipe
Muffler delete
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post #2 of 11 (permalink) Old 28th May 2020, 01:40
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Going by the book, re-add both the cats.

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post #3 of 11 (permalink) Old 28th May 2020, 05:52
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It will pass without front cat.
You need to replace manifold one.
Muffler will make no difference to emissions but depending on your tester he might be an arse about non standard noisy parts
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post #4 of 11 (permalink) Old 28th May 2020, 05:59
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If just one cat readded, then better for it to be stock (more efficient then so called "high-flow" aftermarket cats), and if that only cat is in frontpipe, not headers, well heat up car/exhaust before testing for emissions, as cats need to reach working temps to start work efficiently, and cat in header is in such "bad for performance" location for it to heat-up sooner, so that it cleans exhaust gases better soon after cold-starts, thus cold only cat in frontpipe increases chance of failing.
But in different countries there are different MOT rules. Somewhere there might also be OBD2 checks added in, visual checks (so that everything looks stock). And some countries may have more lax MOT inspections. So worth specifying - passing MOT where.
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post #5 of 11 (permalink) Old 28th May 2020, 07:58
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waffle waffle waffle...........

i can tell you as i have done it.

uk car second cat removed passed mot emission test fine.
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post #6 of 11 (permalink) Old 28th May 2020, 09:37
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... and plenty have failed with just the 2nd cat, church is correct in that the first cat would be better because it gets hotter quicker and will remain hotter for longer compared to the second cat.

as kaviar says though, by the book, you need both cats regardless of it passing the emissions tests
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post #7 of 11 (permalink) Old 28th May 2020, 10:12
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Indeed. I saw posts of failing MOT in UK in twins related forums too, or repeated tests to finally pass by straw.
And heating up increases those chances. Stock cat on frontpipe should be more efficient, as high-flow are not magically better, just marketed with better sounding name, but in reality are simply of less cell count, less expensive catalizator materials used, thus while less resistive to flow, they also obviously do less for emissions.
As for which cat .. removing primary in header nets most performance gains (but needs ecu tune to disable cat tests to not get CEL), also worsens emissions at cold-start. Decat of secondary is simpler, needs no tune (O2 sensors by which Ecu "tests" cat efficiency are before and after primary cat in header), do better with cold-starts emission tests, but less performance gains, no torque dip elimination as with some aftermarket headers.
But if one were to live in eg. California in US, no aftermarket emission modified bits would go through, failing already at visual checks stage and intake/exhaust bits that would be street legal need separate CARB certification most aftermarket vendors not bother with. Here in LV, with also mandatory OBD2 checks catless header may fail at noticed disabled cat readiness checks in tune.
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post #8 of 11 (permalink) Old 28th May 2020, 11:30
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Quote:
Originally Posted by Mike View Post
... and plenty have failed with just the 2nd cat, church is correct in that the first cat would be better because it gets hotter quicker and will remain hotter for longer compared to the second cat.

as kaviar says though, by the book, you need both cats regardless of it passing the emissions tests
If you read what I said....second cat removed not primary cat in manifold.

This is what you need for uk emissions test on mot
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post #9 of 11 (permalink) Old 28th May 2020, 11:35
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I went from your first post of saying it'll pass without the front cat. Doesn't change what church said though, it's not waffle. And it's still correct that strictly speaking you need both cats to pass.
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post #10 of 11 (permalink) Old 28th May 2020, 12:15
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From the Government website: 2.5: A catalyst isnít missing where one was fitted as standard - Which means, if you remove either or both catalytic converter's your car should fail an MOT.
Even if you have only one of the two catalytic converter's fitted and it passes the emissions tests, technically it should still be a fail.

See:
https://www.gov.uk/government/public...cked-at-an-mot
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