[jyl]

The basic issue seems to be distinguishing between the car enthusiast who wants to tinker with his well-maintained car, and the non-enthusiast who just wants to drive his clunking, smoking, gross polluter into the ground.

I'd support using economics to regulate this issue.

If you want to drive a car that's been modified (in a way that could affect emissions) you pay an annual fee. The fee's a sliding scale - a modded engine that keeps the catalytic converter and passes the standard tailpipe test costs $X, to also lose the catalytic converter but still pass tailpipe costs a lot more ($Y), to lose all emissions devices and meet a less stringent tailpipe test costs a lot lot more ($Z).

$X would be fairly modest, like $200-300/yr. This discourages people from simply not bothering to maintain their old clunkers, but still lets enthusiasts do things like SSIs and turbo conversions.

$Y would be high enough to make it cheaper to install a catalytic converter, say $500-600/yr.

$Z would be really stiff, say $2,000+/yr. This is aimed at the guy who wants to drive something really exotic on the street - he imported a Lancia Stratos or something. It is in top condition, well-tuned, not a gross polluter although it might not quite meet standard tailpipe. Fine, he can do it, but he'll have to pay up.

The idea is, if you're a car enthusiast, you get to do all your dream mods and in the meantime spend money, support the aftermarket parts industry, generate taxes for the government, etc etc. Compared to the many $1,000s/yr you already spend on your Porsche, the fee isn't much. But if you're a clunker driver, the fee is enough to motivate you to send old smokey to the scrapyard, or at least install the missing catalytic converter.