Emissions After Tune
 

I want to keep everything nice and legal here. If I get a tune after fitting intake and headers what happens to emissions? Does the extra power that comes from a tune come at the expense of increased emissions or does a proper tune take care of power and emissions?

if you aren't getting a catted header then the tune is the least of your concerns...

Emissions are cut by catalytic converters. If you eliminate any of them, you will have trouble with your emissions. Generally, a tune will increase fuel usage, which may raise your emissions levels a bit in the process, but, for the most part, a properly functioning cat will scrub out most of it (especially an OE cat...high flow cats might have more of an issue because they are more open and, consequently, less effective at removing the harmful stuff)

No emissions tests are done at WOT, so a tune changed only for WOT itself shouldn't change the emissions output of a car during testing conditions. If it increases emissions at WOT or not will depend on how rich or lean it was before the tune as well as after. A well tuned turbo car will be running richer than a good NA tune, so they'll be worse for emissions.

Some tunes actually give better mileage (and possibly emissions) at part throttle, but you could just tune WOT and leave part throttle stock.

Or, flash back to stock for the emissions test. Although I'd do it a few days before, because I think tunes tend to be a bit on the rich side until they learn all the various parameters again. I could be wrong on that, though.

you could probably improve emissions in closed loop just by having more accurate fueling calibration, though i doubt it matters much. i know i picked up some MPG as my closed loop tuning got better.

Is this more like a technical question about how emissions are effected from aftermarket parts and tune, or is it a "if I do x mods, will it cause me to fail this required test in my locality?" question?

And what exactly is the emissions test that the vehicle would undergo? Some places it's idle tailpipe and then two steady state speeds on a dyno. Some places it's just idle. Some places they just look for a trouble code and your diagnostic monitors' readiness. Some places have absolutely zero inspections.

It is a
"So what actually happens? In brief, the car is driven onto the dyno. The gas probe is exposed to air and zero'd. (Calibration of the system has to occur frequently and this is done using an expensive test gas.) The probe is inserted in the exhaust, and the driver is required to place the car in gear and then watch the PC screen. On the screen a narrow 'road' unfolds. The speed of the test car is represented by the location of a small car-shaped symbol on the screen - it's the driver's job to make sure that the on-screen car always remains on the road. The road angles upwards when the car is required to accelerate, alters to being horizontal when the speed needs to remain steady, and dives downwards when the speed of the car must do the same. On the screen the car is coloured green if it's on the road; if the driver wanders off, it turns red. Too many "high speed excursions" will see the test classed as invalid - only a small number of excursions are allowed."
http://www.autospeed.com.au/cms/A_05...ntArticle.html


Catted header is on the shopping list.

Is that the drive trace above? Wow I'm surprised you would have to pass a transient test like that. Is this a cold or a hot test? You could definitely fail that test if the standards are strict enough. The biggest risk would be failing CO due to different enrichment, or failing NOx due to changed AVCS tuning. Or the cat(s) are going to degrade prematurely because the tune caused accelerated thermal degradation of the brick inside.

If it's a cold test any change to the exhaust besides a muffler or catback could make you fail, if the standard is strict enough. You'd be surprised how hard it is to tune an engine for cold starts.

Hot.

Really there are two main risks then. 1 is that, over time your cat would degrade due to the tune and you would fail--but even then you probably won't see it on a hot test. The second risk is that you would fail CO due to enrichment from closed loop delay changes. That depends how heavily the engine is loaded down and how strict the standard is. Closed loop delay has a big effect on CO emissions.

Just to clarify, when I say the cat would degrade... it's not something you would be able to easily see in the real world. From my experience catalyst degradation can mostly be picked up by controlled lab tests. The "catalyst efficiency" check engine light is pretty generous. It only comes on when the emissions are way over standard. And I have no idea how strict the OBD regulations are in your area, so half your diagnostic monitors may note even work.

Again, is there an issue with just reverting to the stock tune for the test?

If all the hardware is stock, it should be fine if you just go back to the stock tune. If you've changed intake and relocated the o2 sensor and such, who knows? Test it and report back.

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Wild guess: I would think an aftermarket header with HFC would cause more extra emissions than any tune.

Well, here's a data point.

We purchased our 2014 out of state, which means that in California, we still have to get a smog check for the car. We went to get a smog check *after* we installed our Jackson Racing supercharger with their CARB legal tune.

We passed smog with flying colors; the tailpipe emissions were nearly non-existent. California has one of the stricter emissions standards in the world.

I'm not surprised. It's all relative. If you're bringing in your catless LS1 Camaro, of course you're going to fail. Even the California emission station tests are steady state, to my knowledge. As long as you have stable comb ustion and high catalyst conversion efficiency all your main tailpipe emissions (HC, CO, NOx) should be basically zero.

The conversion efficiency is down when the engine isn't warmed up, and it's down when the gas feeding the converter is rich or lean of Lambda=1. That occurs during transients (enrichment under acceleration, scavenging with lambda=1, decel fuel cut without enrichment on fuel entry).

Sometimes what people fail is simply the visual inspection--for example, cars with EGR valves blocked off. You probably wouldn't catch that in a steady state tail pipe test, but the inspect will see that it has been removed.