Passing a CAT MOT without cats.

[dnb]

First off, to those who don't know CAT /= catalytic converter.  It just means the modern type of emissions test.

I'd like, if possible to get my Griff through a non-dodgy MOT without a cat.  This is a tall order, but there are a couple of things in my favour:

I have VEMS, which I know is quite good at lambda control.
I have a TVR Griffith, which is listed in the big book of MOT rules as an "exception".

I have to meet the following criteria:
Idle: 0.5% CO
Fast Idle: 0.3% CO; >200ppm HC; 0.9-1.2 Lambda

Will this be possible if I'm lucky?

[Sprocket]

Ooh i too would be interested in this.

I would have thought if you have wideband that you could set the lamda map to 1 around the points they test, so set lambda to 1 right up to 3000rpm at high manifold depression??? not realy knowing how they do a cat test.

Would be interesting to find out.

[rob@vems.co.uk]

You should really have 1.0 lambda around the test regions anyway.

I saw amzing improvements when Gary@APT swapped out old iridium plugs for new NGK copper ones.
That would suggest you want your spark to be the best it can be.

After that its down to luck and a prevailing wind as far as I know, others may have more insights...

Rob

[cliffb75]

Just for understanding, HC is raw unburnt fuel. CO is partly burnt fuel.

Therefore, the things that affect these readings are AFR and combustion quality.

Since both HC and CO are caused by being rich, the first thing you can do is look at running a target lamda that is lean of stoic (lambda 1). Since you've said the rules are as lean as 1.2, I'd start by trying around 1.05 or 1.1.

BUT

Be careful. If you go too lean, you will start to caus epoor combustion, so the numbers will actually go back up again. So there is an optimum value (assuming you keep all other things constant)

Depending on your ignition map, you could also try advancing it a bit. This gives everything more time to burn before the valve opens.

I've heard that laptops are allowed at SVA to set the car up for the test - so hopefully your MOT man will be the same?

[dnb]

My MOT man is quite tame.  He'll be helping me set things up just before the test.

[cliffb75]

In a vaguely related manner (actually because I can't find the right thread....) We were talking about running lean for improved economy.

As I said, I've not tried it, but I'm slowly working my way through 'Introduction to Internal Combustion Engines' by R Stone. In there he states that maximum power is acieved at approx 10% rich or stoichiometric, and maximum economy at approx 10%lean of stoic.

The theory goes that if the throttle is fixed, torque will increase and decrease respectively, but in the case of lean running, the idea is that you open the throttle more to achieve the desired torque, and the reduction in efficiency due to being lean is more than compensted by the improvment in efficiency due to the reduced pumping losses. Obviously as load increases this tradeoff becomes less and less, so you can move smoothly back towards lambda 1 and richer as you get towards the WOT load.

So, the implication is that you should run you cruise loads sites at around lambda 1.1, assuming your engine can tolerate it, for best economy. However, I would still want to be sure I had a pretty good transient fuelling setup to avoid any stumbles as you tip in.

 

[dnb]

That matches my observations.  The thing with a large v8 is that it never really feels like it lacks torque.  (unless it's only running on 5 cylinders!) 

The real trick is finding out where these tradeoffs are.  The fuel use monitor in Megatune may help here as we don't need absolutes, only relative comparisons.

[dnb]

MOT is tomorrow.    Wish me luck - I'm going to try lean burn + no cats!

[rob@vems.co.uk]

Consider your luck wished.

[cliffb75]

Hope it goes OK 

[rob@vems.co.uk]

What was the verdict?

[dnb]

Failed at zeroth hurdle!  (ie non-attendance)

The car - which I think has the same personality traits as a dog on the way to see the vet - had a few tricks left to play on me.  The headlamp dip switch contacts welded together so I couldn't use them, the battery died and one of the ancillary components has developed a distressing loud ticking noise.

[Sprocket]

Well thats a bummer

I will have a go, the Mini is so low, there is no longer any room for the cat, not to mention I dont really want to butcher the new 2" stainless mid section pipe, ooh, 2" single box exhaust It needs an MOT in the next two weeks so if yours is before mine, please keep us updated

[dnb]

OK, got the results of the MOT I managed to attend.  Remember that the car is totally unmapped - just what I put in for running the cam in.

2 MOT fail items: 
headlamp levelling (fixed before I left the test centre) 
natural idle test showed excessive CO

Here's the emissions breakdown:

Fast idle:
CO 0.3% - Pass
HC 85ppm - Pass
Lambda 1.077 - Pass

Natural idle:
CO 2.58% - really bad fail!

By the looks of things VEMS decided to not turn on closed loop lambda for the slow test.  I don't know why, but it does that sometimes.

[dnb]

I surrendered in the end and put a single small cat in the car.  It passed the BET test (that's the standard one that is done before any manufacturer exemptions are considered) first time with no tinkering.

The CO at idle was still high, but I think I had problems with the wideband not turning on again.  Hopefully this is solved by the new firmware - I didn't want to upgrade until it had some miles on as it was just one more variable to bite me...

Now the proper fun can start.