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?

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.

You might find this interesting reading:

InsightCentral.net - Encyclopedia - Honda Insight Advance Catalyst System

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?

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.

It doesn't seem to be bad for the converter.

Isn't it supposed to be, though? The wrong combination of exhaust and insufficient temperature?

You still get HC, CO, more NOx and plenty of exhaust heat even in lean burn.

Maybe water injection could also help on that matter.


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.

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.