SC Tuning to Pass Emissions (some may need for future reference)
Here are the trials and tribulations of having a SC car. A bit of background. I live in a county where emissions testing started in May of 2003. So I got the car inspected 4/31/03 to allow one more year of playing prior to an attempt at passing. The car is an '87 with a bored, stroked, SCed small block, ZF, 3.42 gears. Last time on the dyno it made 740+ RWHP, and I have since upped the boost to 14 (previous just under 10 psi). Best run at previous boost was 10.03 @ 142 MPH. No runs at 14 psi. I program via FAST with wide band (I tried for many years to do the chip thing, but will never go back after moving to aftermarket ECM).
My last inspection expired (Apr '04). Several guys have said they can get the car inspected for a cost of $75-$150 (legal inspection is $39). I wanted to do it legal (we all have dreams).
Test involves two in motion tests (this assumes you pass the visial and safety portion, which I did).
First test low speed emissions (15 MPH; 2nd gear 1250 RPM).
Parameter STD Reading Results
HC (PPM) 157 789 FAIL
CO (%) 0.88 2.65 FAIL
NOx (PPM) 1184 202 PASS
First test low speed emissions (25 MPH; 2nd gear 2010 RPM).
Parameter STD Reading Results
HC (PPM) 152 140 PASS
CO (%) 0.97 2.26 FAIL
NOx (PPM) 1082 249 PASS
All of the above were run in 2nd gear and the same tune that I run at the strip. A/F ratio in the range (500-2000 RPM was in the 13.8-14.3 range).
I discussed with the owner of the inspection station, and he allowed a 2nd run if I could adjust on the fly. Quickly adjusted the A/F ration to 15.2 at all VACUUM levels between 1000 and 2500 RPM. Restarted the test.
First test low speed emissions (15 MPH; 2nd gear 1250 RPM).
Parameter STD Reading Results
HC (PPM) 157 351 FAIL
CO (%) 0.88 1.97 FAIL
NOx (PPM) 1184 205 PASS
First test low speed emissions (25 MPH; 2nd gear 2010 RPM).
Parameter STD Reading Results
HC (PPM) 152 72 PASS
CO (%) 0.97 1.44 FAIL
NOx (PPM) 1082 259 PASS
The 2nd test failed the same as the first. BUT, I nearly cut the HC and CO levels in half, and did not increase the NOx by much with the changes in the A/F ratio. I told thge owner that I would "build" a special program (0-3500 rpm in 300 RPM increments) that would be considerably leaner in the range testedl, and return on 5/14 to try again. The normal program is in 500 RPM increments (0-7500 RPM). I think the owner is quite interested in seeing me pass.
As a side note, the car did not like the tune on the drive home. Tip in was very poor and it did not like it when I nailed the throttle. I will have to quickly change back to the normal program before leaving the inspection station on Friday. Any limit as to how lean the motor can go under light load conditions? Can I go toi 16.0 or even 17.0 at 2000 RPM and 56-85 kPa? The motor sounded like it may have been missing ever so slightly at the 15.2 A/F ratio. That miss might be contributing to the higher HC and CO.
Has anyone gone through this excersize with their car? Advice?
Aaron, do you have cats installed? I fear that I too may someday dun into this problem. I also tune with the fast ECU and was hoping to do exactly what you did by adjustubg the A/F ratio for such a test.... We've got to figure this one out!!!!!
The cats (or lack of) are causing you to fail. We have the same test in Canada and I can pass using my performance tune with cats on. Low A/F ratios are used for wide open while the O2 sensors take over at cruising or idle, this is when the test is done.
Get a set of cats made that allow you to swap out the test pipes. Pass the test then put the test pipes back on.
As detailed in the data above, the tests were run at the lower RPM range (1250 and 2010 RPM, respectively). If I hear what you are saying, then there is no way to pass without the cat. If I am beating my head against the wall, then I probably should just break down and buy the cat.
Anyone have suggestions on a 3.5 or 4" cat that is close to or as short as the stock cat, and that will not add significant flow restriction? It would also be nice if it was not too expensive. It would be relatively easy to swap a cat in place of the straight pipe.
One of my next projects is to upgrade the exhaust with larger piping if the psi tests prove that the exhaust is a restriction.
Guys, I don't know about other states, but in Illinois if you have insurance that states it as a show/race car. Full coverage and liability on the street with a max of 5000-7500 miles a year, you qualify for an EPA waiver. NO EMISSIONS. Any car older than 10 years qualifies for this insurance in my state.
Seeing how you've got room in the NOx to go up some, I'd try more timing. Generally leaner mixes need more timing. The burn time actually slows down the leaner you go. NOx will go up with more timing - increased combustion temps.
In the range in which the test is done, I am already in the 38-44° advanced range. Are you recommending even more? I have no spark knock under full load and 26-28° adv. I am concerned of going further lean, and will it want to run at all. What do very late model cars run for A/F ratio in the low RPM/high vacuum areas?
Does RandomCats make a 4" cat. If so, that would be easy to install.
I will have to ask about the show/race classification. I already have my vettes classified as specialty cars through Leland West with a max allowable mileage on each of 5000 mi/yr. I probably put less than 3000 on it last year.
Don't endanger your motor by running it too lean or with too much timing. It could detonate if you get on the throttle.
I have yet to see any car without cats pass, except for a handful of old school muscle cars that have extremely lax emisions requirements.
Another option is you can ask for a "Hot Rod" category emission test. This is for cars that have a non-standard motor installed that was not available from the manufacturer. It's usually easy to pass under this category if they'll allow you to fit under it.
I still stand by my original recommendation to install cats for the test or "buy" your way out of the test.
I've seen 48 degrees in stock programming. I've also heard of fueling stategies in the 16 to 17:1 A/F. I wouldn't try that lean with a FAST setup. The leanest I've ever seen a FAST wideband sensor read is 15.9:1. I don't think the display will show leaner than that.
With the way you've set up your tables you can command full rich and normal timing in your top rows in your tables which is what the FAST will use for fuel and timing after you excede the max RPM or MAP values in the table.
Cats would have you passing in a heart beat. You still need a lean tune and some signicant timing to keep the cats from glowing bright red. You've got to try to take care of as much of the combustion in the cylinder rather than burning the leftovers in the exhaust.
I have a pipe that "looks like" a cat. Everything else is legal (AIR pipimg, etc.). I spoke with the inspection station about the different catedories, and they all claim ignorance (talk to the state, typical response).
It looks like a cat may be in my future.
As for the comment on detonating, etc, I do not think that self-control will be an issue.
As for the Buy my way out, that was the whole reason I started this process. I want to do it legal.
Aaron, how big is your cam? I am running a 224/236 in my car and with my setup using a OBD1 GM PCM I pass easily with one of my calibrations in my car. But I can tell you that without the cats in the car I would have a much harder time getting it to pass. I would bet that if you get some cats on the car it would fly through easily. Also I have found that taking timing out will clean it up considerably. If you make the AFR go too lean its going to start misfiring and that won't get you to pass at all when that happens.
SloVette you are very correct, I am tuning a FAST system this week with a 434 small block and its WBO2 will not show leaner than 15.9 AFR. For this L98 based car I am going to relocate the O2 sensor to the header collector. For some reason its located on the number 7 tube. It needs to have better overall representative sample of whats coming out of the engine rather than just one cylinder.
If you move the sensor see what the A/F readings do. I think the header manufactures put the sensor as close as possible to where the factory put the sensor in the original exhaust.
No ... running 110 octane is not going to make it pass. Are the CO emission stds consistant with those as listed above? Each state has subtle (some more obvious) differences in HC/CO/CO2/NOx requirements.
Hey Aaron here is another way to make it pass, Add a mix of denatured alcohol into the fuel tank. It takes about 1:10 ratio of alcohol to gasoling to work. Sometimes about half depending on how bad the car fails. I have never had to add more than 1 gallon to 10 gallons of fuel. Thats what I have done here to cars with big cams and they pass like a new 2004 car off the dealer lot! Works everytime with a car that won't pass DEQ around here. And we have a treadmill test at our test stations here in Portland.
Yes i agree with TJwong but we also have to be tested on the treadmill or dyno looking emissions. But my HC/CO/CO2/NOx requirements are super clean with 110 octane? but try TJwongs remedy.
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SC Tuning to Pass Emissions (some may need for future reference)
