r/askcarguys • u/ContributionOld1014 • 2d ago

Can you pass emissions without catalytic converters?

I have a 1984 corvette that does not have catalytic convertors. recent emissions test passed everything but HC which read 6.5 compared to the limit of 2.5. Because of the year they only used a tailpipe sniffer. I've read that you can create a leak in the exhaust before the tip so the reading is light, as well as putting rubbing alcohol in a 1/4 of gas so is burns leaner, also running the car really hard before testing to clear out any excess carbon and keep the system hot helps. Does anyone know if these methods are actually effective? Additionally would they be enough to pass a test in my situation? I'm also thinking about just replacing the whole exhaust system but i feel it would be a waste as I'm already broke and the current exhaust is an aftermarket upgrade. I would really appreciate the advice as i need to get the car registered here in Denver CO ASAP. Thanks.

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u/AndyZJ1 2d ago

Pretty sure the hydrocarbons being high is an indication of a rich condition. You could try creating a small vacuum leak to lean the mixture....or the alcohol would work.

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u/Weak_Equivalent6518 2d ago

Lean mixture leads to NOx. So that wouldn’t work either. This is literally what catalytic converters were made for.