Quietest / Stealth Performance Exhaust?

[Martyn777]

Is there a recommended exhaust that is not much louder than standard, but still as free flowing as some of the louder exhausts?

 

I‘ve got a 3 inch Cobalt cat back system at the moment, which is great in short bursts, but on the whole is too loud for my liking.

So I want quieter but with no loss of power! ??

[ast]

The catback aftermarket exhausts don’t add/free up any power, so if you want quieter, revert back to stock.

[Alec]

@saz9961

The catback aftermarket exhausts don’t add/free up any power, so if you want quieter, revert back to stock.

Agree with above. Also if it’s a MK3, 3.5 or 3.75 the restriction to power is the exhaust manifold.

 

[BrilliantBlackBirdy]

@Alec

@saz9961

The catback aftermarket exhausts don’t add/free up any power, so if you want quieter, revert back to stock.

Agree with above. Also if it’s a MK3, 3.5 or 3.75 the restriction to power is the exhaust manifold.

 

With that in mind. What are the options for a manifold. Do i need to spend £400 at MX5 parts or do the ones on Ebay at £200 called Japspeed work just as well?

 

[ast]

With manifolds, its easy to ruin things by fitting a cheap setup. Why do you need to change the manifold? If you do, you need to decide whether its a 4-1 or 4-2-1 setup you want, and if the main use will be street or track. Different designs will affect drivability. The Japspeed is likely a copy of someone elses. Looking at the photos on their own website, the welds on the header tubes are pretty rough looking. There is some attempt to polish them down. I’d hazard a guess these have never been flow tested.

The MX5parts ILM manifolds claim “maximum HP and a maximum high flow.”, but they use the same description whether for the 4-2-1 or 4-1, so suggests there is a fair amount of marketing fluff. And both £400 manifolds are not UK road legal.

Racing Beat list race headers for the NC, and they have the gumption to publish dyno charts.
http://www.racingbeat.com/Miata-MX5-2006-Present/Exhaust-Headers/56010.html
https://www.racingbeateurope.com/mazda-mx5-nc-2006-2015-racing-beat--exhaust-manifold---super-cup--series--manifold-1584-p.asp

Again, also no more road legal than the MX5parts headers.

[BrilliantBlackBirdy]

Not a case of need rather than want really. Having anything restrict the engine unnecessarily just means its something else i will want to change eventually. 

 

There’s a long list before i get there though.

[Cypher]

I have Racing Beat 4-2-1 fitted - road legal (not sure were this road legal comes from!) passes MOT and with all the other bits changed to the back of the car ups bhp to 181 on paper.

John

[Cypher]

@saz9961

With manifolds, its easy to ruin things by fitting a cheap setup. Why do you need to change the manifold? If you do, you need to decide whether its a 4-1 or 4-2-1 setup you want, and if the main use will be street or track. Different designs will affect drivability. The Japspeed is likely a copy of someone elses. Looking at the photos on their own website, the welds on the header tubes are pretty rough looking. There is some attempt to polish them down. I’d hazard a guess these have never been flow tested.

The MX5parts ILM manifolds claim “maximum HP and a maximum high flow.”, but they use the same description whether for the 4-2-1 or 4-1, so suggests there is a fair amount of marketing fluff. And both £400 manifolds are not UK road legal.

Racing Beat list race headers for the NC, and they have the gumption to publish dyno charts.
MX-5 Miata Header for 06-15 MX-5 - Racing Beat
Mazda MX5 NC 2006-15 Racing Beat Exhaust Manifold Super Cup series Manifold 2 0 & 1 8
Again, also no more road legal than the MX5parts headers.

Can you please explain the comment. I have had mine fitted for 3 years now and informed insurance of the “mod” passed the MOT… I called Racing Beat direct this morning and they are somewhat baffled by this comment. I await your reply with interest.

John

[Martyn777]

@Alec

@saz9961

The catback aftermarket exhausts don’t add/free up any power, so if you want quieter, revert back to stock.

Agree with above. Also if it’s a MK3, 3.5 or 3.75 the restriction to power is the exhaust manifold.

 

Thanks - it’s a mk1 

 

[ast]

@Cypher

@saz9961

With manifolds, its easy to ruin things by fitting a cheap setup. Why do you need to change the manifold? If you do, you need to decide whether its a 4-1 or 4-2-1 setup you want, and if the main use will be street or track. Different designs will affect drivability. The Japspeed is likely a copy of someone elses. Looking at the photos on their own website, the welds on the header tubes are pretty rough looking. There is some attempt to polish them down. I’d hazard a guess these have never been flow tested.

The MX5parts ILM manifolds claim “maximum HP and a maximum high flow.”, but they use the same description whether for the 4-2-1 or 4-1, so suggests there is a fair amount of marketing fluff. And both £400 manifolds are not UK road legal.

Racing Beat list race headers for the NC, and they have the gumption to publish dyno charts.
MX-5 Miata Header for 06-15 MX-5 - Racing Beat
Mazda MX5 NC 2006-15 Racing Beat Exhaust Manifold Super Cup series Manifold 2 0 & 1 8
Again, also no more road legal than the MX5parts headers.

Can you please explain the comment. I have had mine fitted for 3 years now and informed insurance of the “mod” passed the MOT… I called Racing Beat direct this morning and they are somewhat baffled by this comment. I await your reply with interest.

John

 

Take it up with MX5parts. The race spec Mk3 manifolds they sell removes one of the catalytic converters.

 

RB’s manifold removes the original secondary catalytic converter, and replaces it with a repositioned secondary item. RB Europe does state “this will pass”.

The secondary catalytic converter incorporated into the mid-pipe section (aft of the manifold section) is retained, this means the car will still pass an emissions MOT test.

 

The manufacturer, Racing Beat, takes a different line:

the secondary catalytic converter incorporated into the mid-pipe section (aft of the header section) is retained. Since a factory-placed catalytic converter is being removed by the install of this component, this race header is NOT considered emissions legal for street use. Both primary and secondary oxygen sensors are retained and are relocated into the header outlet collector. (Although this configuration will not affect engine performance, it is possible that this configuration will trigger an error code with the OBDII system and illuminate the “check engine light” on the vehicle.) To avoid this from occurring, we offer an optional Race Header Wiring Kit that relocates the secondary oxygen sensor.

 

 

MX5parts makes the following comment:

 

Please Note: As from January 1st 2012, the UK MOT laws changed regarding catalytic convertors. Any vehicle built after 1992, MUST have a catalytic convertor fitted regardless of whether or not it passes an emissions test. Any car presented without a cat fitted will fail. Effectively, these stainless manifolds remove one of the two convertors fitted to the Mk3, so we have no choice other than to recommend that they are for off road use only. As your car would still pass an emissions test wth one of these manifolds fitted, it is unclear as to whether or not the one remaining cat is sufficient, so we would advise checking with your MOT tester before fitting this manifold if the car is being used on the road.

 

These statements from MX5parts is fairly damming:

 

These are now supplied with an oxygen sensor relocation kit which is required to fool the ECU into thinking the first cat is still there and stopping the MIL light coming on.

 

 

RB makes their manifolds for the US market. You likely spoke to their Europe distributor. RB make very clear that their manifold cannot be fitted in California. You should see advice from the authorities whether tampering of one of the catalytic converters constitutes tampering with the emissions equipment of the car. You can take the car to an official DVSA test centre for checking, rather than depending on the view of the MOT tester.

 

Further, the question of removal of secondary catalytic converters (MX5parts item) has also produced the opinion of other testers that this will be a fail

https://www.pistonheads.com/gassing/topic.asp?h=0&f=66&t=1712376

https://www.renaultsport.co.uk/forum/default.aspx?g=posts&m=1168030

Toyota MR2 - MR2 Pre Cats | Technical matters | Back Room Forum | Honest John

https://www.pistonheads.com/gassing/topic.asp?h=0&f=70&t=1425831

 

The authorities are cracking down on DPF removal, once they have accurately determined which vehicles shoud have one fitted (apparently not straightforward). I can imagine other examples of emissions equipment tampering would be in their sights.

Heres a new one:

 

https://www.pistonheads.com/gassing/topic.asp?h=0&f=10&t=1158417

 

MOT inspector passing an aftermarket cat “if it has a kite mark”…

 

The rules introduced in 2012, from one reading, would push towards retention of original catalytic converters. RBs note about CELs might indicate they think its a bit marginal.

 

[BrilliantBlackBirdy]

@Martyn777

@Alec

@saz9961

The catback aftermarket exhausts don’t add/free up any power, so if you want quieter, revert back to stock.

Agree with above. Also if it’s a MK3, 3.5 or 3.75 the restriction to power is the exhaust manifold.

 

Thanks - it’s a mk1 

 

@Cypher

 

Apologies for hijacking your thread with all this Mk3 stuff!

@saz9961

With manifolds, its easy to ruin things by fitting a cheap setup. Why do you need to change the manifold? If you do, you need to decide whether its a 4-1 or 4-2-1 setup you want, and if the main use will be street or track. Different designs will affect drivability. The Japspeed is likely a copy of someone elses. Looking at the photos on their own website, the welds on the header tubes are pretty rough looking. There is some attempt to polish them down. I’d hazard a guess these have never been flow tested.

The MX5parts ILM manifolds claim “maximum HP and a maximum high flow.”, but they use the same description whether for the 4-2-1 or 4-1, so suggests there is a fair amount of marketing fluff. And both £400 manifolds are not UK road legal.

Racing Beat list race headers for the NC, and they have the gumption to publish dyno charts.
MX-5 Miata Header for 06-15 MX-5 - Racing Beat
Mazda MX5 NC 2006-15 Racing Beat Exhaust Manifold Super Cup series Manifold 2 0 & 1 8
Again, also no more road legal than the MX5parts headers.

Can you please explain the comment. I have had mine fitted for 3 years now and informed insurance of the “mod” passed the MOT… I called Racing Beat direct this morning and they are somewhat baffled by this comment. I await your reply with interest.

John

The removal of the first cat is where the issue arises. Although the car will still pass the emissions with just the rear (and usually even a race rear) the fact that the car used to have two Cats is enough to enable the testers to fail it on that alone. It’s a very rare thing to happen as the vast majority of testers either don’t know about it having two cats originally or don’t care as long as the machine spits out the right numbers.

 

[ast]

@BrilliantBlackBirdy

@Martyn777

@Alec

@saz9961

The catback aftermarket exhausts don’t add/free up any power, so if you want quieter, revert back to stock.

Agree with above. Also if it’s a MK3, 3.5 or 3.75 the restriction to power is the exhaust manifold.

 

Thanks - it’s a mk1 

 

@Cypher

 

Apologies for hijacking your thread with all this Mk3 stuff!

@saz9961

With manifolds, its easy to ruin things by fitting a cheap setup. Why do you need to change the manifold? If you do, you need to decide whether its a 4-1 or 4-2-1 setup you want, and if the main use will be street or track. Different designs will affect drivability. The Japspeed is likely a copy of someone elses. Looking at the photos on their own website, the welds on the header tubes are pretty rough looking. There is some attempt to polish them down. I’d hazard a guess these have never been flow tested.

The MX5parts ILM manifolds claim “maximum HP and a maximum high flow.”, but they use the same description whether for the 4-2-1 or 4-1, so suggests there is a fair amount of marketing fluff. And both £400 manifolds are not UK road legal.

Racing Beat list race headers for the NC, and they have the gumption to publish dyno charts.
MX-5 Miata Header for 06-15 MX-5 - Racing Beat
Mazda MX5 NC 2006-15 Racing Beat Exhaust Manifold Super Cup series Manifold 2 0 & 1 8
Again, also no more road legal than the MX5parts headers.

Can you please explain the comment. I have had mine fitted for 3 years now and informed insurance of the “mod” passed the MOT… I called Racing Beat direct this morning and they are somewhat baffled by this comment. I await your reply with interest.

John

The removal of the first cat is where the issue arises. Although the car will still pass the emissions with just the rear (and usually even a race rear) the fact that the car used to have two Cats is enough to enable the testers to fail it on that alone. It’s a very rare thing to happen as the vast majority of testers either don’t know about it having two cats originally or don’t care as long as the machine spits out the right numbers.

 

 

The RB manifold has a secondary catalytic converter, albeit one that is not factory, and which has been repositioned from factory.

 

I’m not surprised MX5parts is selling theirs with a caveat (Buyer beware), somewhat surprised RB is so bullish without some sort of statement from the DVSA that it is fully compiant with the post 2012 regulations.

[Cypher]

Firstly,  saz9961 thank you for the reply. I’m currently waiting a email reply from BBR GTi as they also fit these manifolds. I also went to local MOT center this morning and they have NO directions (perhaps as you say) yet.

I also quoted your comment “the vast majority of testers either don’t know about it having two cats originally or don’t care” and he stated “really! so my MOT License, criteria set by the DVSA would be removed if I failed to follow the set guidelines” Daft comment he stated.

Then your quoting rules introduced in 2012… we are now in 2019 and as the MOT center told me until he is told other wise it passes.

Just in case you think I’m using a back street garage I take my car to a MX5 specialist (all be it a 95 mile round trip) so he must know what is required. I have also stated I have RB manifold.

At the end of the day your points are valid and I respect that, but your use of the words “manifolds are not UK road legal” are not

Until things change at the MOT station I’m happy with my setup and therefore still road legal to use as it has a current MOT

John

 

[BrilliantBlackBirdy]

Daft eh?

 

Here is the section covering such items in the MOT manual:

 

8.2 Exhaust emissions

8.2.1 Spark ignition engine emissions

8.2.1.1 Exhaust emission control equipment

This inspection is only for vehicles that must have a full catalyst emissions test (disregarding the basic emissions test). You only need to check components that are visible and identifiable, such as catalytic converters, oxygen sensors, and exhaust gas recirculation valves.

Defect	Category
Emission control equipment fitted by the manufacturer: missing, obviously modified or obviously defective	Major
An induction or exhaust leak that could affect emissions levels	Major

 

https://www.mot-testing.service.gov.uk/documents/manuals/class3457/Section-8-Nuisance.html#section_8.2

You’ll note that Emission control equipment originally fitted by the manufacturer that is missing, is a major fault and therefore a failure. While up on a ramp the first Cat is easily identifiable as missing so should be a fail.

[Cypher]

@BrilliantBlackBirdy

Daft eh?

 

Here is the section covering such items in the MOT manual:

 

8.2 Exhaust emissions

8.2.1 Spark ignition engine emissions

8.2.1.1 Exhaust emission control equipment

This inspection is only for vehicles that must have a full catalyst emissions test (disregarding the basic emissions test). You only need to check components that are visible and identifiable, such as catalytic converters, oxygen sensors, and exhaust gas recirculation valves.

Defect	Category
Emission control equipment fitted by the manufacturer: missing, obviously modified or obviously defective	Major
An induction or exhaust leak that could affect emissions levels	Major

 

https://www.mot-testing.service.gov.uk/documents/manuals/class3457/Section-8-Nuisance.html#section_8.2

You’ll note that Emission control equipment originally fitted by the manufacturer that is missing, is a major fault and therefore a failure. While up on a ramp the first Cat is easily identifiable as missing so should be a fail.

You really should read the FULL post… Daft comment: “the vast majority of testers either don’t know about it having two cats originally or don’t care”

NOTHING to do with the MOT guide lines…

John

[BrilliantBlackBirdy]

OK I went back and read the FULL post again. 

 

My original statement: Most either don’t know or don’t care regarding the use of 2 cats originally.

 

Your comment regarding the MOT testers comment:

 

“really! so my MOT License, criteria set by the DVSA would be removed if I failed to follow the set guidelines” Daft comment he stated.

 

I return with the guide lines (still current whatever year it is) he should be following stating that the removal of a cat is a failure.  Fitting of an aftermarket manifold that does not include a cat is therefore not MOT compliant.

 

There are many on here that have these manifolds fitted and are passing MOTs just fine. To me that says either the MOT testers don’t know there were supposed to be 2 (which is obviously their best defence should they be caught out) or they don’t care as long as it passes the computer test and has at least 1 cat fitted.

 

And there’s nothing wrong with back street garages.

[ast]

@BrilliantBlackBirdy

OK I went back and read the FULL post again. 

 

My original statement: Most either don’t know or don’t care regarding the use of 2 cats originally.

 

Your comment regarding the MOT testers comment:

 

“really! so my MOT License, criteria set by the DVSA would be removed if I failed to follow the set guidelines” Daft comment he stated.

 

I return with the guide lines (still current whatever year it is) he should be following stating that the removal of a cat is a failure.  Fitting of an aftermarket manifold that does not include a cat is therefore not MOT compliant.

 

There are many on here that have these manifolds fitted and are passing MOTs just fine. To me that says either the MOT testers don’t know there were supposed to be 2 (which is obviously their best defence should they be caught out) or they don’t care as long as it passes the computer test and has at least 1 cat fitted.

 

And there’s nothing wrong with back street garages.

 

And so-called visual Smog checks cannot be audited.

[ast]

@Cypher

Firstly,  saz9961 thank you for the reply. I’m currently waiting a email reply from BBR GTi as they also fit these manifolds. I also went to local MOT center this morning and they have NO directions (perhaps as you say) yet.

I also quoted your comment “the vast majority of testers either don’t know about it having two cats originally or don’t care” and he stated “really! so my MOT License, criteria set by the DVSA would be removed if I failed to follow the set guidelines” Daft comment he stated

 

Not a comment from me.

 

Technically he has to follow a manual, not a set of guidelines. Guidelines are just that, guidelines.

 

If he failed to follow the guidelines, the tester would need to demonstrate that he carried out a legitimate test.

[BrilliantBlackBirdy]

FWIW I quoted the manual. I called them guidelines. My mistake

 

My last comment on this as we have hijacked a na thread with nc nonsense.