Re: [DML] free flow exhausts-legality?

[William T Wilson <fluffy@xxxx>]

On Fri, 10 May 2002, nbrommer2k wrote:

> What is the legality of such a free-flow exhaust in the US? And what 
> kind of repercussions would such a system have on emissions tests?

It depends on how free-flow it is. :} Generally, federal law prohibits
tampering with the emissions control system. However this federal law
really only applies to companies, they do not care about what individuals
do. For your own personal use, state laws are what is relevant.

In general, "cat-back" exhaust, that does not touch anything from the
exhaust manifold to the catalytic converter, is legal. This is enough to
pick up a small amount of power and change the exhaust note, if you don't
like it. This is not considered part of the emissions system.

Removing or hollowing out the catalytic converter is not legal. If you
happen to live in an emission-controlled area, you will never pass
emissions. If you don't live in an emission-controlled area, it's still
illegal, but no one will really care as long as the result isn't too
loud.

It is possible to replace the catalytic converters with modern,
aftermarket high-flow models. A modern performance cat is almost as open
as no cat at all. This will require a little bit of engineering savvy to
size them properly, but nothing exceptional. This is technically legal
only if your current cat has failed. (If your car is high mileage, it's
probably plugged up already). Aftermarket cats do not tend to last for
more than a few years.

Headers (in the American sense of tubes that flow directly from the engine
exhaust ports, not the British sense which means exhaust manifold) are
generally not legal, however whether anyone cares is another matter. 
States that do not perform visual inspections in their emissions tests are
not likely to care, states that do perform them probably will care. It
*is* possible to combine headers with an aftermarket cat and get good
performance. Of course, headers have no impact on actual emissions
whatsoever, provided that a proper cat is in place. They have a large
impact on noise, which might make your exhaust illegal on that count.

If you live in California, any aftermarket emissions-related parts must be
CARB-certified to be legal. This includes the air intake, for some
reason, modification of air intakes is legal in some states and not
others.

> One more: What does the cost translate into American Dollars?

Probably 500 to 3000 dollars depending on how much you do and quality.