So I am thinking of putting a straight pipe on my Mjet from the cat back , can someone tell me if this is legal and will it pass an MOT with one?

I very much doubt it would be legal due to the noise! Without any silencers, it would be too loud.

As said above:rumour:
Noise level would be too high for MOT purposes, definately would need a small silencer.
Im sure i read somewhere even cars for track days have noise levels to adhere to.

It will be absolutely fine. With it being a diesel and the fact you're leaving 2 cats in it won't be much louder at all. I have straight through from turbo back and no mot issues whatsoever.

A straight pipe on a petrol however, particularly a naturally aspirated one, is a whole different kettle of fish however.

Smeduz said:

So I am thinking of putting a straight pipe on my Mjet from the cat back , can someone tell me if this is legal and will it pass an MOT with one?

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I don't think so, but you can't tell if it's legal without measuring the noise level. Note that the police don't have to measure the noise level to give you a ticket, just that it is louder than normal in their opinion. Also do you literally mean a "pipe" or a straight through silencer? Just because someone else has "got away with it" does not mean it's legal. It's easy to give advice when you are not the one paying the fine or getting the points.
It IS grounds for an MOT failure. From the testers manual section 7.1 http://www.motuk.co.uk/manual_710.htm
Method of inspection:
4. During all parts of the emissions test relevant for the vehicle, assess subjectively the effectiveness of the silencer in reducing exhaust noise.
Note: For vehicles not subject to an emissions test, the engine should be revved to around 2500rpm or approximately half maximum engine speed if this is lower.
Reason for rejection:
4. A silencer in such condition, or of such a type, that the noise emitted from the vehicle is clearly unreasonably above the level expected from a similar vehicle with a standard silencer in average condition.
Highly subjective - yes, but still a fail for a straight pipe if the tester is diligent.


Don't forget to tell your insurance company or they may refuse to pay out on a claim. A straight pipe is a pretty obvious modification. Yes they have to pay 3rd party claims, but that does not mean they can't come after you to get the money back. A non declaration followed by an (unrelated to exhaust) injury accident could result in you literally paying for the rest of your life.


Robert G8RPI.

Cheers guys! Will have to do a bit more research with it with the silencer side of things

In the past I ran a Discovery 300tdi with no boxes at all-straight pipe all the way from the manifold with a side exit behind rear wheel and that went through 3 MOT's with no problems-and it was bloody noisy!
Also ran a Freelander diesel and Polo diesel with straight through pipes as well with no problems.

soggytomato said:

In the past I ran a Discovery 300tdi with no boxes at all-straight pipe all the way from the manifold with a side exit behind rear wheel and that went through 3 MOT's with no problems-and it was bloody noisy!
Also ran a Freelander diesel and Polo diesel with straight through pipes as well with no problems.

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Still doesn't make it legal
The only thing we can say for certain from this is the MOT tester was not very diligent.


Robert G8RPI.

Jacob said:

It will be absolutely fine. With it being a diesel and the fact you're leaving 2 cats in it won't be much louder at all. I have straight through from turbo back and no mot issues whatsoever.

A straight pipe on a petrol however, particularly a naturally aspirated one, is a whole different kettle of fish however.

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Agreed highly likely that it will be pretty quiet if you retain the front part. Can you remove the existing pipe and hook something up temporarily as a check before committing to a straight pipe?

g8rpi said:

Still doesn't make it legal

The only thing we can say for certain from this is the MOT tester was not very diligent.


Robert G8RPI.

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This was 4 different testers or locations over a 6 year period!

Thinking back I also did the same to a Cavalier 1.7tds about 12yrs ago-that did fail the mot though but not on noise-it was just falling apart!!

soggytomato said:

This was 4 different testers or locations over a 6 year period!

Thinking back I also did the same to a Cavalier 1.7tds about 12yrs ago-that did fail the mot though but not on noise-it was just falling apart!!

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That just shows that the MOT system is not working. I'd hazard a guess that non of the test stations sold exhausts. Why would to do it anyway?


Robert G8RPI.

All of the test stations where garages as well and did all repairs and servicing.
On the discovery it made a massive difference. Engine revved smoother and quicker and with the turbo and fuelling tweek more power.
Not sure it would do a great deal on newer diesels without some other forms of tuning and setup but it certainly makes the diesels rev better.
Only downside is that if you do remove the cat or particulate filter on older models it will smoke like a chimney!!!

Only thing I can suggest is to take off the boxes you want and fire it up and see how noisy it is! Adding the straight pipe won't make much difference but will send the noise to the rear of the car rather than coming from underneath!
Like I said, I didn't have problems but this was a few years ago now so they may have tightened up a bit but there's a few discovery's around us with straight through systems as you can hear them coming!

I've an 08 1.3 mjet 500 passed its Mot last month. I did a back box delete and put twin pipes instead of the letterbox. As mentioned above the dpf and cats do the vast majority of the silencing. The sound of the car changed only slightly. A slight change in tone rather than volume I found. I've convinced myself the weight save was a good enough reason as any.

Tom

Would anyone know how easy it is to remove the exhaust from the turbo or cat back?

I have a 1.6 jtd and Tony banks in Leeds made my stainless exhaust, he suggested no silencers at all and said it would only have a slight note of sound, he makes these for a living and his fabrication is amazing. I'm old so just had a rear box in the system but he knows his stuff.

Always amazed at the "did you tell your insurance company" quotes, At this rate if you car came new with Michelin tyres and you replaced them with Dunlop would this be classed as a modification! same as different brake pads etc etc! If a vehicle passes a test laid down in law I fail to see the relevance of this. Unless you are asked directly and answer untruthfully, what constitutes a "Modification"?

New exhaust system is 100% classed as a modification and you must tell your insurance. It's pretty obvious really, exhausts are probably the most common modification.

digger58 said:

Always amazed at the "did you tell your insurance company" quotes, At this rate if you car came new with Michelin tyres and you replaced them with Dunlop would this be classed as a modification! same as different brake pads etc etc! If a vehicle passes a test laid down in law I fail to see the relevance of this. Unless you are asked directly and answer untruthfully, what constitutes a "Modification"?

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A modification is a deviation from the manufacturer's specification. Changing a Dunlop 155/80/14 tyre to a Uniroyal 155/80/14 is not a modification. Changing to a Dunlop 175/65/14 is and should be declared (unless it's listed as an option in the handbook for that specific car level trim and wheel size). Pattern pads or disks are no issue, "performance" pads, drilled or grooved disks are and again are instantly obvious to an assessor. For the last 20 years or so, every time I've insured a new (to me) car I've been specifically asked if the car has been modified and all the policies have had a requirement that I notify the insurer immediately of any modification. It's not "don't ask don't tell" it's you don't tell, you may pay later. I've never been charged more for a stainless or slightly tuned exhaust, but I have had an assessor question one on my car after a no-fault accident, saying that they would not pay for a replacement as it was non-standard. Quick delve into the paperwork for a copy of the letter telling my insurers and suddenly no more problem.
Tell your insurer of any modification, it's too late after an accident.


Robert G8RPI.

So with that thinking you should examine a new to you car and compare the spec to original. That would be interesting with brake pads especially! So called performance pads can fit the standard caliper, performance clutch? What about a car passing your MoT test or our NCT, will they pass with non standard equipment? I have yet to see any Insurer fail to cover any vehicle once they issue a policy, even in cases where monthly installments have lapsed!