Emissions question

[ringram]

Just wondering if any of you guys especially with HSV's and aftermarket exhausts have any issues with emissions compliance.
I know one or two that do have issues and they have cats!
Anyone with a 52 reg Monaro and catless exhaust gone for testing yet?

Just interested to know if the stock engine will pass without cats.

[stevieturbo]

From what I have been led to believe, no petrol engine today can pass the requirements without a catalytic convertor.

Its the only reason car manufacturers fit them in the first place.

[V8D]

OK guys, heres my experience.
I have 04 cv8 with wortec's stuff done ie CAI, Headers, loud straight thru with no rear box and no cats. Remap etc.
On my Crypton analyzer she gives .23% CO and Lambda 1.003 Easy MOT pass incl HCs. This was at Idle, they check at 3000 rpm as well and no probs at all. (similar numbers.)
Discussed this with an MOT tester pal of mine and he says for type approval, cats must be fitted. Period. However, once you own the car you can do what you like, so long as you comply with "statutory emissions limits". He says if you pass the test, you get yer ticket. Sounds simple enough doesnt it?
One point, if you just take the cats off, you will fail by miles as they seem to run rich in the stock tune to keep the cats lit up. Once you retune to run the correct FAR (leaner)the emissions come tumbling down. I get 10 - 15% better mpg after the mods as well!
Hope that helps
V8Dave

[ringram]

In theory at warm idle and 3000rpm the O2 sensors stock, or tuned will be keeping it at stoich as they tell the PCM when to pull or push more fuel in based on the "closed loop" fueling thats built into the PCM. I think the only way it will be richer at part throttle is if the sensor switch points (millivolts) have been altered.

Certainly under load you are correct and they do run rich.

[V8D]

Interesting point here. Lambda sensors are only looking at the O2 content. They have no idea what the CO is doing, although 02 is a direct measure of AFR as I understand it, so long as theres no air leaks in the exhaust. The VM isnt too bothered about CO and HC as they know the cat will clean it up to an acceptable level. CO is a measure of the efficiency of the burn, and is affected by engine characteristics etc as well as fuelling strategy. My mon gives CO of .23% with lambda at 1.002, but if I adjust the vette (Holley) to lambda of 1.002 the CO is around 2%. Neither has a cat fitted. Maybe Paul or one of the tuning specialists can explain this better!
V8Dave