One middle ground option to consider on the cat (between cheapest and OEM)
is the cali CARB approved cats.

I don't want to start a flame war here about CARB but van-cafe does say on
their page that they notice a "dramatic" improvement in emissions when
installing them:
http://www.van-cafe.com/home/van/page_1678_275/catalytic_converter_calif_wextras.html

Anyone with first-hand experience (testing before and after)?

On Fri, Jun 29, 2012 at 12:37 AM, Dennis Haynes <d23haynes57@hotmail.com>wrote:

> Proper maintenance, testing and operation is the key. The combustion
> process has not changed over the years, only the tolerance of the controls.
>
> Start with the fuel system. Make it is tight and that the vapor recovery
> system works. This controls hydrocarbons being released into the air from
> evaporating fuel.
> Do not over advance the ignition timing or during rebuild consider engine
> modifications such as cam-valve lift/timing or increasing compression.
> These changes and maybe even some engine conversion increase the production
> of NOx. Make sure the O2 sensor system is working properly and at catalyst
> replacement time consider the big bucks of OEM. I have yet to see a
> replacement cat have as much material as the original.
> If you area has an emissions test program and you fail, get it fixed?
> Working right it will pass any states-local requirements easily. Failures
> for our years always mean something is wrong. No temporary adjustments or
> magic chemicals should be needed.
>
> Then there is all there other stuff such as tires and alignment and brakes
> not dragging. Slowing down can also make a huge difference. If 30% more
> fuel is used at 70 vs. 55 not only do you make 30% more greenhouse
> gasses/mile but the increased loading will further increase the production
> of NOx which the Water boxer does not have EGR to help control it. The
> three way cat and O2 sensor have to do it.
>
> Dennis
>
>