What base timing for LEAST emission?

[awdclipse]

Right now my car is set at 5 degrees BTDC but i want to retard it a little and try to lean it out for better emissions. I am really not concerned about performance just as long as the guy can drive it on the dyno. Ive read to retard it somewhere around 4 degrees is that 4 degrees past the stock 5 or just 4 degrees base timing? If anyone has any input please let me know im heading over there tommorow. Andd my MAS is completely stock with all honeycombs right now would taking out the lower one create a more lean/better condition?

*all other emissions related repairs have been done but still have a 1% high hydrocarbon count everything else is fine.

 

[perley03]

Leaning out your a/f ratio will contribut to hotter burn, thus increasing your NOx count. At high temperatures, usually above 1200°C (2200°F), molecular nitrogen (N2) and oxygen (O2) in the combustion air disassociate into their atomic states and participate in a series of reactions. These reactions will result in the hydrocarbon Nitrogen Oxide (NOx).
They will detect your high NOx count and fail your emissions, putting you back to square one. If your car doesn't pass emissons right now, find out what failed it and fix it from there.

 

[awdclipse]

I think it may because all vacuum/emissions systems has been removed from my car during the motor swap, but ive heard of many people easily passing without them..what the hellll???

Welll what if my NOx's are low and i have some allowence for them to go up and still be under the accepted value???

 

[perley03]

If your NOx values are under the maximum amount, then you won't fail that part of the test. I'd say go ahead and try it. If you fail, ask them what failed and tell them to be specific, so you can try to figure out what exactly has to be done to pass emissions. I see that you are AWD, does this place your going to have an AWD dyno??? If not, all they can do is just do an idle test, which is where i would try to lean it out and see if it will pass. Let us know your results, what you did, etc.....and keep us posted.

 

[slipstream808]

Hmmmmm...

To be REALLY honest, tuning for emissions would be like tuning for power:
Get the dyno goin' and strap on the emissions equipment. No bull.

Here's a BASIC of how it works. Too rich or cool, hydrocarbons. Too hot (usually meaning too lean), Nitric Oxide.

Now though, since dyno time doesn't seem to be an option, you needs a lesson.

Advancing timing will cause more burn in the cylinder, and less out the exhaust. So this will decrease hydrocarbons, as the flame is burning as it was intended. BUT this will increase temperatures inside the cylinder (more flame in there!!). So you will have an increase in NOx. And this is visa versa for retarding timing.

AFRs. 14.68 is "ideal" for complete combustion. But does that happen... no. So richen it up and you'll increase your hydrocarbons. Lean it out, and you MIGHT up NOx, depending if you are at idle or cruising. Idle wont be as bad since there is no load on the engine, and things are going slower. Cruise around and you'll see some changes. As the AFR gets leaner from 14.68, NOx will go up. Until you get lean enough whereby the flame decreases, and things get cooler in the chamber with the excess air and NOx goes down. But that's not for us to worry about!

Problem is for you, how do you plan on leaning things out? The ECU will try to keep that stoichiometric mixture, even if you were to lean it out or richen it up. You'd need an aftermarket device to control your oxygen sensor's target AFR. So all you can really do, is advance your timing, not retard it. Keep us informed. And update your mod list. It might give me something I can work with.