Reducing emissions and maintaining power

[Calgary280ZT]

I think of myself as a reasonbly green kind of guy, but I'm also building my car for lots of giddy up and go. I searched and didn't find much on this topic, thought I would ask.

 

I'm installing MS this spring. I have a 3" exhaust. If I run a lean tune for day to day driving and install a high flow cat, what will my emissions like be? Would I pass a California-style test?

 

I currently live in Alberta, where everyone drives a big pickup or SUV and there are no emissions requirements...in fact, burning more hydrocarbons is considering to be "supporting your idustry." LOL So I have never smogged a car and know little or nothing about meeting emissions standards.

 

Anyone from one of the strict states (e.g. California) have any information or observations?

[Tony D]

With a catalyst you are stuck running 14.7:1 AFR for proper catalyst operation.

If you lean out considerably from that point, the cat has a problem lighting off and sustaining catalytic action to properly scrub the exhaust.

 

If you take a look at some of those AFR charts that chart NOx, CO and HC, you will find that you can get REALLY clean by running leaner, though at the expense of NOx that skyrockets.

 

I could lean out my 71 SU carbs to pass a tailpipe test for a catalyzed 83 car! That was pre-rolling roady dyno testing, and I KNOW the NOX was skyhigh. But the CO and HC were CLEAN! When the 73 gets refitted with EFI, I will not be running a catalyst, but know the CO and HC will be low enough that I will sleep well at night knowing I'm clean. It's also why I keep that Federal 75 2+2 out back. The thought of a "NON CATALYST" stock EFI Z-Car appeals to me, as I know without the cat, it can still be clean.

 

If you discount the NOx issue, you can be very clean CO and HC wise.

 

Keep this in mind, though: Over 3500rpms, and over 75 or 80mph, almost every car produced is in 'open loop' mode anyway! The cat is along for the ride then as there is plenty of heat being forced down the pipe to keep the cat working on a three way catalytic action.

 

Some catalysts can be set up to attend to the NOx issue. Stationary powerplants using Recip Engines (natural gas fueled) run super lean, like 22:1 AFR, and run special catalysts to attend to the NOx.

 

I digress...

 

Tune the car for both...really! Your car will be light loaded when cruising and can be tuned 'lean' while once you get to say 54Kpa, or above 3500rpms, and/or say 40% throttle opening your fuel mixtures can take a quick jump to the 13:1 and richer ranges for maximum power.

 

Really, you aren't concerned with 'max power' at a throttle opening at any rpm that would produce say, 40kpa in the inlet manifold so tuning that bin lean would give you fuel economy as well as the lower emissions (CO and HC wise) that come hand-in-hand with that tune.

 

After 50 or 60 Kpa and 40% throttle opening you are definately "on the throttle" and want the rich mixture for maximum power and to decrease your EGT's if you are holding it at that point for a long time (like high speed runs at 100+mph across I-80 between SLC and Reno...er...uh...theoretically speaking...yeah, 'theoretically speaking'!!!)

 

Really, though, the car should pass emissions testing without a catalyst at all. The catalyst scrubs 'excursions' like that quick acceleration burst when you are running the FACTORY fuel curve at 12:1. When you are light cruising, the catalyst is basically along for the ride and not doing too much...if your fuel curve is proper.

 

I am awaiting a full Allen Diagnostic Machine for the house. My bud got one from Delaware. Apparently it was the same machine Del was using for emissions testing till recently. If you can pass a simple tailpipe sniffer test at idle and 2500 with a good five gas readout you will know what your engine is doing. If you can take that same test on a rolling road and make your own decision on power versus emissions output, all the better. Tune it where you have the balance you want, and then you're done!

[Shift]

I forgot who, but there's a guy on this forum that has a stroked turboed L28 and said he was getting like (I want to say) 27-35 mpg(?). I think thats a goo start. Might want to search for that.

[ktm]

I can tell you that my Wolf'd L28 with the T03/04E setup is running cleaner than the old 1972 L24 with SUs simply by the amount of exhaust fumes that permeate my car.

 

Before it was bad, even with the smog pump and stock smog equipment operational. Now there is almost no exhaust smell whatsoever with the windows down.

 

I am running around 14 to 14.5 when cruising and up to close to the pressure ranges Tony talked about. I go a little bit higher simply because when driving up a hill in 5th gear your manifold pressure will increase (I typically see 7 to 10" vacuum when going up hill cruising).

 

I am going to lean out even more and target 15:1 when cruising as well as bump my timing up to 42 or 44 degrees. Right now I am running 40 degrees when cruising.

[Calgary280ZT]

Tony, as usual you lost me after "Hello"....LOL Save those thoughts for Chez Calgary at MSA and if I feed you a case of Moosehead or Schooner maybe your answers will make sense to Ole Mr. Ten Thumbs.

 

Bo, good info, makes sense to me. With the stock EFI I'd say I'm running rich, judging by the smell. Not too bad, but some. BTW, looks like it's Megasquirt instead of SDS...turned out to be an economic decision as much as anything.

 

Shift, I already get high 20s with stock EFI running 70-75. Anything over that and MPG drops to low 20s. With all the head/intake mani work I've done/plan to do, I hope to get low 30s (based on posts on this forum). That's the story my wife bought to justify the cost of the mods, so I'm sticking with that number....LOL

 

So, the lesson I'm taking away from this discussion is that a properly tuned engine will get me to where I want to go and a cat won't really add much?

[Tony D]

The cat won't TAKE much is a better way to look at it.

 

The cat may cost you fractional horsepower.

 

But the mixtures you will need to run to ensure it is actually catalyzing will cost you fuel mileage.

 

IMHO it's better to just run it leaner and pump out more NOx than to run it rich for the sake of a catalyst's operational happiness.

 

Frankly, I have not looked into Three Way Catalysts too much (which is what I think you need to take NOx down)...

 

If you run enough EGR under light cruise, I think NOx will be considerably reduced. And because a Turbo Car is so low in the compression ranges anyway, the NOx production is inherently less anyway.

 

If you could put the car on a Five Gas Analyzer and run a rolling road dyno test on it after your mods, you could see where you are and where you could make improvements.

 

Really the way OEM's do it...they make power first, then work on drivability and emissions compliance. (Not to say they don't think about emissions in design...but when it comes to ECU tuning, this is the steps they go through.)

 

Power first, emissions, then work to ge the best compromise between emissions compliance and drivability.

 

If you work on Power first, then drivability...you will be happy. Then find that five gas analyzer and a dyno...and decide what compromises you want to make and 'how clean you want to be'...

 

I'd skip the Catalyst until you get it up and running. If you don't need it for compliance right now, just run the car and tune it clean as you can.

 

If you enable O2 correction and standard narrow band O2 sensor, you can easily slap a cat under there and see for yourself what kind of improvement out the tailpipe you will get. At idle you would make 'nothing' frankly...as long as the cat is hot enough to keep working at idle that is!

 

I digress, and ramble....