Dadic 78

I need to lower my NOx in order to pass my emissions test.

I'm running a stock tune, virtually stock motor... Shorty headers, with all the EGR, and smog stuff still on. Got a CAI, low temp stat, Magnaflow Cat.

I've read (and heard) that the Cat/EGR are the two main contributors to lowering a vehicle's NOx. My Magnaflow Cat is brand new, and although it's a high-flow, I've heard of many F-Body guys using these cats and passing emissions.

Now I'm starting to lean towards the EGR itself. I've got a new one coming this week. I'll swap them out and see how it goes, but I'm wondering if anyone here has a concrete answer on exactly what controls the NOx values in an LT1, and where I should be looking specifically to lower them.

Thanks.

94Z28rag

iTrader: (10)

Put your stock thermostat back in. The hotter it runs, the cleaner it will run, too.

Dadic 78

That's the tricky part about NOx... The hotter the cylinder temps, the higher the NOx values will generally be. So, in this case, it's not beneficial to be running hot, hence why the "get it real hot" method isn't working for me, nor will the alcohol in the gas tricks.

From what I've read, it's primarily the Cat, and EGR that will control the final NOx reading. I'm swapping my EGR this weekend, then I'll try another E-test.

In the meantime, if someone here can add any info they may have on NOx, I'd greatly appreciate it.

djjab57

iTrader: (17)

Ive heard good things about the stuff you run in the gas tank, just cant remember the name of it right now

airfix

iTrader: (30)

I had this exact problem, I got a Piece of clear oxygen hose (like they have in the hostpitals) And by passed the egr solinoid, So run the vacum hose off the intake mainfold straight to the egr valve. Now the egr valve will work strictly on engine vaccum not by when the solinoid opens/closes, Just like how an ols school engine would work. My car was running Slightly hot I did this and It lowered the nox a bit.

fleetmgr

You've got it backwards. The higher the combustion temp, the lower the Nox will be. Thats why cars in the last 30 years have had 190-195 stats. In the '60's and '70's you saw 170-180.

Also, CAT's have a minimum threshold temp the exhaust needs to be before they work well. With a 160 stat, you probably won't get there.

Raven97

Fleet is right it all relates to being more efficient during the combustion cycle, the hotter the burn the more complete and efficient it is

94Z28rag

iTrader: (10)

Not true. Put the stock thermo in and let her get to around 220 and I'll bet you'll pass. The Cat works more efficiently when the exhaust temps are higher as well.

YodiBrodi

some of y'all are right about catalyst efficiency being best at higher exhaust temps, but way wrong about about how NOx is formed. it IS formed at higher combustion temps, oxygen and nitrogen fuse at temps of something like 1400-1600 F and during the rich burn cycle NOx is reduced. the lean burn cycle converts the hydrocarbon and carbon monoxide emissions. that's why O2S switch between rich and lean, for the catalyst to work properly. the EGR's sole purpose is to reduce this particular gas by actually lowering combustion temperatures, a rich condition is introduced when the EGR is open (exhaust gas is low in oxygen) and thereby creates a rich air/fuel ratio which reduces cylinder temps. a hotter running engine is more efficient but will not reduce NOx emissions, the proper emissions equipment is required for that. a fat tune will reduce NOx but may put you at risk of exceeding HC emissions. my '95 passed in july, texas emissions standards, no cats, no EGR, but ran a PCMForLess tune, just barely though.

Wicked94Z

iTrader: (26)

i'd say your egr isnt functioning properly, or you've got a **** ton of carbon in your combustion chambers creating hot spots.