When I had the BBR Super 220 conversion done to my ND I queried the available options of a catted or non catted manifold, as obviously the catted manifold is more expensive and creates a loss of 2 bhp compared to the non catted manifold. It was explained to me that the catalytic converter fitted to the manifold reduces emissions whilst the car is warming up and reaching normal operating temperature whereafter the mid pipe catalyst takes over. The current MOT test conducts emissions testing only when the car is warmed up to normal operating temperature. It was explained to me that the car would not fail MOT emissions testing with the non catted manifold option. However in order to future proof any possible changes to the MOT emissions requirements and also to ease my conscience I went for the catted manifold.
Sounds fair - as the one in the manifold will heat a lot quicker. And as you say, by the time you get to the MOT station it will be warm - if they do it straight away, but if you have to leave it, there may be more of a problem if the engine/exhaust gets coldâŚ
if they do it straight away, but if you have to leave it, there may be more of a problem if the engine/exhaust gets coldâŚ
Direct copy from the manual. (DVSA-In Service Exhaust Emission Standards for Road Vehicles. Paragraph 1.2).
Wherever possible vehicles should arrive at the test station with the engine at its normal operating temperature (e.g. after a drive of approximately 5 miles). Before carrying out the test, the Tester will confirm that the engine is at its normal operating temperature which, in some cases, will require the use of an oil temperature probe inserted into the dipstick tube. Before proceeding, the tester will also check that the engine has sufficient oil and fuel to complete the test.
Thatâs absolutely correct - itâs what I alluded to earlier when I said that our current UK test is different to the criteria needed to be met by Mazda.
I think that is what I said. The tester needs to ensure the engine is at proper operating temperature before it is emissions tested. You should ask the tester to make sure that the car is properly warmed up and at the correct operating temperature before the car is emissions tested. If the tester cannot confirm that, you should not accept any emissions related fail.
Yes, but you as the customer know full well that if youâve removed any emissions devices youâll go for a drive before having the test done to get it warmed up. If it still had the factory cats fitted you wouldnât need to.
Yes I know, just showing for others if they may be interested.
In addition- That is the DVSA advice whether cats have been removed or not.
Many thanks.
OK. Thank You.
Took the wifeâs little 1.0l turbo fiesta for MOT just yesterday.
Fully warmed up on arrival and left running whilst checking lights etc.
Then turned off for 10-15 mins whilst up in the air for the underbody, steering and brake mechanism checks.
Restarted for emissions and I had to hold at revs for a couple minutes to get it warm again as the emissions were outside of limits, prior to starting emission procedure.
Totally standard car, low emissions, zero road duty, but it would still fail until properly warmed up, as I suspect most modern cars would even with the manifold cat.
Many thanks for the positive input.
Yep, thatâs exactly why the DVSA give the advice to the testers to warm it up to operating temperature before the emissions test.
That has been advised for many decades that I am aware of.
Otherwise a fair few standard cars would be failed. Thanks once again for sharing your experience. 
Yet iâve seen cars taken cold off the forecourt, taken in for a test and passed on emissions.
So there is the question, why does an MX5 have two cats, yet when the same engine used in the same year of saloon car only has one big cat?
Most likely is the lack of space under the car to accommodate a âbigâ cat??? Just guessing realy.
I said that I would not respond further to you.
However, on this occasion I will and give you âmy answerâ and hopefully you can accept the DVSA procedures and people have different opinions, move on and let other people have a go. Just because we have different opinions or views does not mean anyone is right. That is just the way of the world.
Without going into lengthy detail of why a Catalytic converter needs to be hot.
Inside (amongst other metals/materials) the special expensive metals, rodium, platinum and palladium can be used.
Thatâs why people steal them for the precious metal.
Quite simply the special metals that are coated onto the honeycomb structure of the Catalytic converter need to be âhotâ for the structure to function and work properly. That is how it is designed and that is the fact of the item and not even my view or my opinion. Likewise, that is another subject and indeed a different topic perhaps.
My understanding why the MX5 NC has 2.
The United States of America in particular California realised back in the 1970âs that they really needed to do something about the out of control Emissions of the vehicles on the roads.
They therefore tightened up on vehicle emission outputs a lot more than nearly every other state at the time. However, other states very quickly realised the issue and followed suit and therefore all these states emissions were a lot tighter than the rest and indeed the world including the United Kingdom.
As time passed, âany carâ that was exported or sold into this market had to meet more âstringent emissions outputâ. Manufacturers found themselves having to modify vehicles specifically for this market, hence why you will see different specifications of engine outputs of the same car/engine around the world. Likewise, the same engine in the same car âcan/mayâ have slightly different ECU programs, with different software mapping, different ignition, exhaust, fuel and inductions systems to meet the different emission markets. As I said previously you have to look at the bigger picture.
Quite simply the MX5 NC (called the Miata) in the USA was a big seller during its time.
My understanding is Mazda took the route of designing the âPre Cataytic Converterâ within the manifold specifically to cater for that market due to tighter emissions. Also the MX is a smaller car and accommodating and designing makes life more difficult too. So they opted for the 2 on that model. The same engine in different bigger model cars (Ford) clearly didnât need 2 and was designed with 1.
The inline second one is the Main Emission control item and will work quite satisfactory within the UK market, (IF the item is in good working order). If it didnât it would not be passed by our MOT testers.
Yes, I know some cars have kept the front one and deleted the centre one. But that proves how good they both are and perhaps Mazda also put 2 on as a âJust in case belt and braces jobâ for that marketâŚ
However, to save costs and to keep the vehicle simple across the board they obviuosly used this design for the whole of the World Market. If you have to design different manifolds for different markets it costs more in design time, materials, moulds, fabrication etc etc and indeed more money resulting in the consumer paying more.
The whole world is gradually catching up with each other as time passes and hopefully we will all be the same in due course for many reasons.
My understading, interpretaion and opinion.
It is packaging yes, but itâs due to lack of space to the side of the engine.
The MX5 is the odd one out when it comes to the cars these engines are fitted to. Itâs mounted longitudinally whereas all the others are transverse.
When itâs transverse the exhaust exits out the back under the floor beneath the centre console.
After the 4 - 2 - 1 manifold itâs straight into a single larger cat. Because itâs close to the engine it heats up quickly and does its job.
There simply isnât the space by the side of the engine in the MX5 to get a sizeable cat in there so they split it into two smaller ones.
IIRC from an emission standard point of view, for an engine to meet EURO4 or EURO5 (not sure which) it must meet the exhaust emission limits within 30 seconds of stating the engine, the âclose coupled catâ (or Warm-Up Three-Way Catalyst [WU-TWC] as Mazda refer to it, the down-stream one is referred to as just a Three-Way Catalyst [TWC]) allows the MX-5 to achieve this.
That is my understanding of why the catalyst location was moved closer to the exhaust on most vehicles. It is intended to get the catalyst up to operating temerature much faster.
JS
Many thanks for that.
Likewise, itâs daft that the designers have to go to lengths and expense to do that, but our MOT system is clearly not the same.
Just checked and the NC started life as Euro 4
Changed in 2011 to Euro 5.
Amended the original text to suit.
So, it was a wise decision to go for the catted manifold on the BBR Super 220 conversion?
Depends on context I suppose, from an MOT point of view which is how this topic started off, depending on how an MOT Tester interprets the MOT Testerâs Manual then it could well be a wise choice.
The rules are worthless. If the tester decides itâs a fail he will fail it. âYouâ (random person) spouting rules and regulations will make no difference. Itâs like going to the headmaster and telling him he has marked your homework wrongly, even if he has you wonât win, heâs in charge and wonât appreciate some cocky idiot telling him how to do his job.
Best thing to do is make tour own choices in life. And deal with the consequences as they arrive. Arguing on the internet with other people who have no more idea that you do is pointless. We all know how to circumnavigate the MOT system if need be, either youâre happy or you ainât, Iâll take my own chances. That said I like stock cars as they left the factory so Iâm not worried about mine. Used to like to mod cars as a kid tho.