K series w headers and Convertor?

[SunSoaked]

Is there anyone out there with a 4wd (k10/20/30) that's running headers with catalytic convertors?

I know...if you're using headers you're not likely using convertors but, I am and I'm tired of the fumes.

It just looks "challenging" on my options for fitting everything under the truck. Looking for ideas.

[Warrens69GMC]

You have to have converters in Yuma? I thought it was just Tucson and Phoenix areas.

AFAIK if you are smelling gasoline fumes and put on a catalytic converter, the converter can collect all of the unspent fuel and then the combustion happens in the converter

[SunSoaked]

They aren't required in Yuma.
The fumes I'm referring to isn't unburnt gasoline. I have a fairly new (6500 mile) crate engine and a well tuned Multi-Port EFI. As with any engine, it produces byproducts of combustion and they are not pleasant. Its most notable at idle obviously but they do find their way inside or worse yet inside my garage/house if I'm sitting in the driveway.

With todays convertors, there's no reason not to have them. Just a personal preference. My wife has lung issues and she can smell it a mile away and it makes her cough something horrible yet she could suck the exhaust pipe on my 2021 duramax with a smile on her face.

[kwmech]

If you are smelling fumes with an MPFI engine it is running too rich or needs a different tune or chip. It may not be as well tunes as you think. Find a shop with a 4 gas machine willing to probe the pipe to see where your readings are

[SunSoaked]

I've had this argument with a friend of mine who insists that there should be no emissions if I'm running EFI.

If that's the case why does every single vehicle produced have efi and one (or two) catalytic convertors?

I don't believe its possible to "tune" out all the byproducts of combustion.

Example:

To achieve the best power, all of the air has to be used as efficiently as possible, so the mixture will be enrichened by adding more fuel. The AFR for maximum power is usually between 12-13:1, depending on how well mixed the vapour was beforehand.
The extra fuel increases the likelihood of the free oxygen being closer to a fuel molecule for the reaction. Some fuel will be wasted as there is an excess in the cylinder, but it helps ensure all of the air is used to it's full effect.
Likewise, running lean is better for economy. Where economy is concerned, you are looking to use all of the fuel injected by having an excess of air. Free oxygen taken into the cylinder will be wasted but the priority for an economic tune is to avoid wasting fuel.
Lean running will increase the temperatures of the combustion, and will also make more of the Nitrogen in the air oxidise into Nitrogen Oxides (NO and NO2, Nitrous Oxide is N20 and a different kettle of fish). The excess heat if unchecked can cause engine and Catalytic Converter damage, and the NOX is an undesirable air pollutant.

This chart shows the resultant gasses from burning petrol at different AFRs. Rich mixtures are cooler but you can see the increased Hydrocarbon emissions as the excess fuel is unused. Nitrogen oxides are low from the cooler temps, but Carbon Monoxide is far higher with the lack of free oxygen to convert the CO to CO2.
Lean mixtures around 16:1 AFR produce the best economy, but the extra heat oxidises the Nitrogen in the air increasing air pollution, but with low CO levels. Leaning the mixture further past this point creates lean misfires with the mixture failing to completely combust, lowering temperatures (and therefore NOx levels). The Hydrocarbon (HC) levels start to rise as unburnt fuel exits the exhaust and power drops off.
The Stoichiometric ratio of 14.7:1 can be seen on the chart which provides a good compromise between power, economy and emissions, and this is the target for closed loop operation.

[Just call me Sean]

Originally Posted by SunSoaked

I've had this argument with a friend of mine who insists that there should be no emissions if I'm running EFI.

If that's the case why does every single vehicle produced have efi and one (or two) catalytic convertors?

I don't believe its possible to "tune" out all the byproducts of combustion.

Not no emissions, low emissions. EFI should have low emissions. Yes, you can't tune out all emissions but you can tune out more than you are.

And the main reason why vehicles have EFI and converters is because some guy wrote something on a piece of paper (statute, code, regulation).

[kwmech]

You're right, you cannot tune out all the hydrocarbons from an engine. BUT if it smells soooooo bad that nobody can stand it there is other tuning to do. That's why I recommended a 4 gas print out revealing the CO--HC--O2 and CO2. CO is unburnt fuel as in running too rich. HC is the engines ability to burn that fuel. For example if the engine is running at say 2-3% CO and the HC is in the 3-400 ppm it probably is running too rich. However if the CO is at 1% and you have the same HC I'd say you could have low compression or a misfire. O2 and CO2 also have a say but that is the basics without getting into which cam you are running and how much overlap. Throwing catalytic converters to clean up the mess is a stop gap measure that will either over heat the converter resulting in the famous rotten egg smell or possibly burning the vehicle down if it is running rich

[Ziegelsteinfaust]

It sounds like you need a tune bad, and maybe even new plugs.

My carburetor LT1 350 with a choppy cam does not put out much in the way of fumes. Because I tuned it as far as I could before my afr crapped out. I have been near desmogged LS engines with fuel injection that were alot worse then me.

[Corts60]

Originally Posted by Just call me Sean

And the main reason why vehicles have EFI and converters is because some guy wrote something on a piece of paper (statute, code, regulation).

Literally everything we follow in the world is because somebody wrote something on a piece of paper, like the constitution and whatnot.

OP, why not just go with rams head manifolds and high flow cats? If comfort is more important than HP, seems like the easier route. I understand where you are coming from. My ‘88 burb with TBI had the cat deleted before I got it and it is noticeable just by the smell. Not a rich smell, just an obvious smell there isn’t a cat installed.

[Just call me Sean]

Originally Posted by Corts60

Literally everything we follow in the world is because somebody wrote something on a piece of paper, like the constitution and whatnot.

Maybe everything you follow, but I don't do things just because somebody wrote it on a piece of paper. I live my life the way I wish, not the way some guy wrote I should live it.

[DoubleDubya]

On my 1985 k1500 GMC I have long tube headers and two cats. Dual exhaust with no crossover. I still get some "rich" smelling fumes but it's not too bad. I'm sure that some fine tuning on the carb would help.

[Mike C]

8500 gvwr after 1979 and 6200 gvwr before were exempt from converters. At least through ‘85. So all the K20/K30 guys probably wont have them. Just the K10.