MOT - Modded cat... Exhaust Valve position?

[Krhuangbin]

Had my 4.3 cats effectively primary decatted by Bamford Rose recently, and they fitted their 3 way hidden switch.

This basically leaves you with 2 x 400cell cats, so emissions are OK.

However I drive around, as I am a yob, with the valves fully open all the time..... this is likely a stupid question but should I close them for MOT?! I.e fully closed, not in dynamic mode?

[Caslad]

I seem to remember reading something about MOT testers failing cars for excessively loud exhausts. Never come across it myself but in view of this I tend to leave my 3-way switch in quiet mode for the MOT.

[Krhuangbin]

Cheers

[Dewi 2]

An interesting point.

My early 4.7 has the same mod as yours, but I did not give any thought to that when I took it for MoT at a main dealer.
The switch was probably set to Open when my car was with them for test.

The BR mod does not alter the external appearance of those cats in any way.
I cannot find a photo, but are those cats hidden by removable undertrays?

The emissions figures have been unchanged since the mod.

[raceboy]

Fuse 22 was pulled on mine the week I bought it, been MOTed every time since with the fuse out never had any issues.
I'm not entirely sure but I believe an MOT tester can fail a car for being 'excessively' noisy but in reality unless it make their ears bleed you'd be fine, my de-cated TVR never had any issues and that made the Vantage sound like a Prius.

[Calinours]

Mine is effectively straight through, tuned length stainless headers, 200cell cats and a fully bypassed back box when the valve is open. It does make your ears bleed, especially in a tunnel. I got an advisory about an excessively loud exhaust when I forgot to close the valves once, but it still passed.

It probably depends on the individual tester, whether or not he’s having a bad day, has a headache, hangover etc.

[DB9S Paul]

From the government MOT Rules

[i]8.1. Noise
,
Hide
8.1.1. Noise suppression system
You must inspect:

exhaust silencers
under-bonnet noise deadening material fitted as original equipment - you do not need to inspect this for Class 3 vehicles
You must use your judgement to assess exhaust noise:

during the emissions test for the vehicle
rev the engine to around 2,500rpm or half the maximum engine speed if this is lower on vehicles not subject to an emissions test
Exhaust noise from the vehicle must not be unreasonably above the noise level you’d expect from a similar vehicle with a standard silencer in average condition.

Defect Category
(a) Exhaust noise levels in excess of those permitted Major
(b) Any part of the noise suppression system:

(i) insecure
(ii) likely to become detached

Major
Dangerous[/i]

My DB9 is decatted and has a Vanquish rear box, which in effect is straight piped and has no problem.

[Krhuangbin]

All good, passed no issue with the valves open

I was also very interested to see the emissions after having the cat mod and relying solely on the 17 year old second brick in the can…..

absolutely no issues

[Dewi 2]

Krhuangbin said:

... I was also very interested to see the emissions after having the cat mod and relying solely on the 17 year old second brick in the can …

Are your latest emissions figures almost the same (mine are), as those in previous MoTs, before the cat mods ?

[Krhuangbin]

Yep, pretty much exactly the same. No idea how that’s possible but goes to show how restricted these were from the factory, exhaust wise

[Dewi 2]

Krhuangbin said:

Yep, pretty much exactly the same. No idea how that’s possible but goes to show how restricted these were from the factory, exhaust wise

We are lucky not to have cats in the manifolds.
Think that began in about 2010, which then made achieving a good exhaust sound more expensive.

[DB9S Paul]

The reason for the extra cats (primaries) is to reduce emissions quickly after startup, this is needed to achieve euro 4, 5 etc. but is not part of the MOT, the MOT just measure the emissions when the car is warmed up.