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Old 04-18-2017, 11:55 PM   #1 (permalink)
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Catalytic converter for lean burn

To make my stroked out, high compression big block as inconspicuous as possible I want it to look like a normal vehicle (above and below), sounding normal with converter and muffler and smell normal, not belching off unburned fuel.
Normal engines try to keep the air fuel ratio as close to 14.7 to 1 as possible under about 99% of the run time.
Normally Catalytic converters seem to clean exhaust that shifts rapidly between slightly rich and lean or will go rich briefly.
But my tune runs about 18 and 16 to one at idle then going down the road it runs 15.5 and 16.5 to 1.

The suburban because it is a 1985 and 3/4 ton appears to be emissions exempt according to the stickers I found in the engine bay and on the motor.

Not too worried about the exhaust being restricted because it will have an electric cut out.

Can a normal converter run lean pretty much continuously?

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Old 04-19-2017, 05:56 AM   #2 (permalink)
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It should work okay.

It will still oxidize HC and CO but will no longer reduce the NOX.

In the past before the NOX limits became particularly tight, some lean burn cars did exactly this though the converter was an actual 2 way cat.
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Old 04-19-2017, 10:28 AM   #3 (permalink)
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You might find this interesting reading:

InsightCentral.net - Encyclopedia - Honda Insight Advance Catalyst System

Quote:
The insight is designed to operate at a very lean air fuel ratio during light throttle cruise conditions. The mixture can be as lean as 22:1 if conditions allow. This provides very good fuel economy, and low HC and CO emissions. However, the lean mixture also causes a rise in combustion temperature, and high NOx production is the result.

In order to prevent high NOx tailpipe emissions during lean burn operation, the Insight uses a dual catalyst system that includes an extra NOx storage/NOx reduction catalyst.

The 3-way catalyst is closely coupled to the exhaust manifold to minimize heat-up time, thus reducing emissions after a cold start.

Lean NOx Catalyst Functioning

The lean NOx catalytic converter is comprised of a ceramic A1203 substrate, a platinum (Pt) catalyzing surface, and a titanium-sodium (Ti-Na) NOx storage surface.

During lean burn operation, the exhaust gas contains a larger percentage of oxygen (O2) and NOx, the NOx being primarily nitrogen monoxide (NO). The platinum catalyzes the O2 and NO to produce nitrogen dioxide (NO2), which is able to be stored on the Ti-Na surface.

When it determines that the Ti-Na surface is saturated, the Insight temporarily richens the mixture. This action decreases the NOx and O2 in the exhaust, and raises the levels of hydrocarbons (HC) and carbon monoxide (CO). The platinum is then able to use the HC and CO to catalyze the NO2 (that has been stored) into harmless nitrogen gas (N2), carbon dioxide (CO2) and water vapor (H20).
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Old 04-19-2017, 12:08 PM   #4 (permalink)
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I just can't get the engine to run very well with air fuel ratios greater than 18:1 I get the air and fuel exploding in the intake manifold, kind of like a nitrous pop with out the nitrous. If I regear, run a lower cruise RPM and add more timing maybe it should work.
Last time it happened I was sure I blew the butter fly valves off the carb, then I assumed the engine ingested them and I thought I may have capped my self.

I'm not real worried about reducing the NOx because this is one of the windiest places in the nation and there is no smog. Lots of dust but no smog.
I just don't want to clog or melt down the converters, because they are $60 to $80 each and I will need 2 of them. If the price of platinum and palladium go up replacements could cost a lot more. That would mean driving around with the cutouts wide open till I could get it fixed.
I mainly want them so I can have a some what restrictive factory style exhaust that will:
reduce noise.
I believe a little back pressure will increase cruise fuel economy.
Eliminate CO because it's deadly.
Reduce HC because it stinks.

There actually is some CO and HC in a lean burn. About as much HC and CO if you are running 14.7:1 air fuel maybe even a little more.

That insite converter sounds like the gasoline version of a diesel catalyst. When it gets saturated with the undesirable NOx substance it has to make like a diesel and burn more fuel to get rid of it.
I'm kind of against burning more fuel for slightly cleaner emissions.

I know I had read some where the factory lean burn cars had different converters but I didn't know what made them different.

Do we know if any one has had problems putting a normal converter on a lean burn car?
I'm assuming the correct lean burn converter is expensive so this likely has happened at some point?

Do we know if anyone has figured out how much fuel the factory NOx regen burns?
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Last edited by oil pan 4; 04-19-2017 at 12:19 PM..
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Old 09-29-2017, 01:55 PM   #5 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
Do we know if any one has had problems putting a normal converter on a lean burn car?
I'm assuming the correct lean burn converter is expensive so this likely has happened at some point?
I thought I'd resurrect this thread to see if you've found any answers to this. I'm starting to experiment with lean burn at light engine loads and don't want to wreck my cat.
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Old 09-29-2017, 04:02 PM   #6 (permalink)
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It doesn't seem to be bad for the converter.
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Old 09-29-2017, 04:41 PM   #7 (permalink)
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Isn't it supposed to be, though? The wrong combination of exhaust and insufficient temperature?
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Old 09-29-2017, 07:04 PM   #8 (permalink)
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You still get HC, CO, more NOx and plenty of exhaust heat even in lean burn.
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Old 09-30-2017, 02:00 AM   #9 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
I'm not real worried about reducing the NOx because this is one of the windiest places in the nation and there is no smog. Lots of dust but no smog.
I just don't want to clog or melt down the converters, because they are $60 to $80 each and I will need 2 of them. If the price of platinum and palladium go up replacements could cost a lot more.
Maybe water injection could also help on that matter.


Quote:
That insite converter sounds like the gasoline version of a diesel catalyst. When it gets saturated with the undesirable NOx substance it has to make like a diesel and burn more fuel to get rid of it.
I'm kind of against burning more fuel for slightly cleaner emissions.
In a Diesel it usually resorts to a post-injection at the exhaust stroke, which is only doable because of the direct injection. Otherwise an extra injection would be required at the exhaust.
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Old 09-30-2017, 04:52 AM   #10 (permalink)
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If you run water injection during cruise or light load you will likely loose fuel economy.

The insite is a gasoline engine so to regeneration the NOx catalyst the ECU can just riches the air fuel mixture. The NOx will turn back to nitrogen and oxygen all on its own, eventually.

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