Need to throw my $.00000002 in I'm FAR from a tree hugger, but I recognize good function when I see it...

I had a nice turbo back exhaust with a flow thru muffler put on and didn't notice until later that they didn't put th cat back in... so about a week later I had them install it and there was NO difference in performance or fuelage that I could tell.... only difference was that a LITTLE of the turbo whine was eliminated...

Your inference that the cat removal is what saved you fuel is somewhat misleading...
There are SO many variables with mpg that the difference between having a cat and not is negligible if at all...
Having changed so many things at once, it would be impossible to isolate one change that creates the difference.

Others have done more extensive testing than I with dynos and time slips with and without the cat and the differences were not statistically significant.... right in line with the air temparature difference or traction difference, etc...

I'd seriously consider leaving the cat in since there is no proof of a difference and it actually DOES reburn the exhausted fuel charge...

Anyone ever had a firebox with a catalytic element on top ? They function best with a slow smolder rather than a burn... and emit tremendous amounts of smoke and unburnt fuel...

On mine I could take the hot plate off the top exposing the cat element and you could SEE how much hotter it was compared to the firebox charge... Somewhere in the 2500 degree range if I recall correctly.... and NO smoke would come out of the chimney....

I mean to each his own... but it does help emission with no detrimental effects so why remove it ? we all have to breath that air...

And I would guess the cost of the cat is less than the upwards of $10,000 fine you COULD get from the Federal government for defeating your emission equipment...

course, I like whistling into the wind sometimes

 

As I changed the whole exhaust system at once, (the air filter system was change some weeks earlier) I suppose that it is possible that leaving on the cat wouldn't make much difference. I do know that the latest group of Caterpillar engines on semi trucks now have cats and the fuel economy was significently reduced by their addition. I'm sure that the backpressure they create is the problem. On the newer diesel trucks with higher horsepower, dual exhaust is now required to help reduce the backpressure problem. Everyone who is considering the removal of their cat has to consider the possible problems with the emission laws. I'm confident that 90% of my fuel economy improvements are due to the removal of the cat. As far as environmental variables, the temperatures have only been getting hotter. I would expect fuel economy to go down as the temperature goes up and the A/C is cranked up. It gets warm around here. It was 109 yesterday.

 

SBV,

Put it in the garage & save it. I really think that in 07, most states will start requiring testing of diesel exhaust (particulates if nothing else). The cat is a rather spendy item, if you have to go buy another. I understands the design of the diesel cat is to help burn off unburned particles that otherwise would go out the pipe as smoke.

I know that there is a lot of restence to governmental interferance (I personally think the morons at CARB have been hanging aournd tail pipe emissions so long their brains have rotted), but w/out them we'd look like Blackpool in the 1890's, and I wouldn't want to live in that.

Just saying that keeping the cat, rather than destroying it could be some cheap insurance in case the rules change again.

Yeah, I'm running 5/38 (B-13) on a regular basis. That's about all I can afford right now. If I could afford the $2.96/g + road tax, I'd run B-100 summer, and B-50 winter. The stuff is just fine for these rigs, if you buy a commercial grade that meets the ASTM standards. What the auto makers are trying to cover them selves on is if someone gets bad home brew. If you follow the proceedures right, hame made is fine too, but it is a finiky process. The biggest problem being residual water in solution. That is bad for the injectors.

There are plenty of TDIs & Trucks running around here & europe on the stuff w/ no problems at all. W/ B-13, I get 18mpg unloaded & there is no loss of power at all. For all of you here, please look into bio-diesel, and seriouslly consider using as much as you can afford. It has the potential to save this country from ruin (take your pick, environmental, financial, political, geo-political.) Just check out the web site you find doing a google search. Diesel designed these engines to run on peanut oil, and if we go back to that we'll have the future available.