Damn, where are you located if you don’t mind me asking? was it parked somewhere for a long time?

Sure, I’m in White River Junction. Just parked at my house, but I’m on a main street where people tend to walk by at night. Not unheard of for random guy to be yelling at the world while walking by, etc. Some are veterans, some are unhoused and sleep under a nearby bridge, and we have our share of overdoses etc etc. Not saying that’s related, just that the area is not without stuff going on. People are struggling with their rents being unaffordable. Still surprised me, though I’d been hearing that my generation of Prius was a prime target. They busted a big ring in the state the day before mine was stolen.

I’m an armchair sociologist 🙄

Didn't they catch two of these thieves just this week? If I remember correctly, they operated all over the state.

Correct, 2 men and a teenage boy, caught just before mine was stolen:

https://www.wcax.com/2022/11/08/vermont-state-police-arrests-made-200-catalytic-converter-thefts/

I mean, you’re not wrong.. people are desperate as can be these days. Really shitty that your cat was stolen, it’s possible you could run a test pipe, but that’s not super great for the environment. I did find this, without knowing your year I took a guess.. title of post clearly says 07 lol. This might be more what you’re looking for

Your car is going to run like total crap. The exhaust back pressure will be too low and the O2 sensor(s) will over compensate. Probably will recirculate too much through the EGR valve. Will get terrible fuel economy and the engine will be very weak. Not sure that it would damage the power train, but you will notice a difference.

Not accurate. You can fuck things up by putting on way too small of a cat so you’re actually creating excess back pressure, but there’s no such thing as too little back pressure and unless you’re totally choking the exhaust, the computer will adjust and you won’t notice any difference.

Of course you can over-restrict the exhaust. Engines are designed to operate in a back pressure range. Too high or too low, and they don't work right. Especially if the engine has an EGR system. You are flat out wrong about not noticing a difference.

Yes, there is absolutely such thing as too little back pressure.

I'm saying you can overrestrict, but you can't underrestrict. And if you buy a normal-sized aftermarket cat, you aren't in danger of overrestricting. These things are not that picky.

FWIW, I spent a decade fucking around with the exhausts of seven different POS lemons racecars. I've fucked around with every possible cat-delete configuration on a bunch of japanese and american cars. Modern emissions systems are really really tolerant and have enough map range to accommodate almost anything an amateur mechanic can throw at it. These are not high-strung race cars operating at the edge of their envelope. They're grocery-getters built to keep running fine under all kinds of environmental and maintenance conditions. Chill.

Cool story bro. I've designed engines for CAT and Cummins. I know a thing or two about emissions systems and engine back pressure. You just don't realize that your "tuned"/deleted engines aren't running the best they could. You also aren't giving enough credit to the Prius's power train. It is pretty advanced for a mass produced auto product.

Wrong wrong wrong. The only job of the secondary or downstream o2 sensor (after the cat) is to tell the ecu the cat is working. The upstream o2 sensor does all the fuel adjustment... The car will throw an emissions CEL for the missing cat but it is 100% harmless for the engine to drive without a Cat on a prius as long as the upper resonator and upstream o2 haven't been cut out.

For the future inspection, OP should shop around at exhaust shops for pricing. Possibly even find a shop that allows bringing your own part, saving extra cash.

Thanks very much. I just was not sure whether a garage will put on an aftermarket part like that. All very confusing - some places online I see talk about $2-3K for replacement but then there are lots of 07 Prius cats listed for about what you linked. I will in all like.I hood be getting a new car before inspection in August but trying to see what options o have until then. Thanks again!

Yeah no, but I agree with your second paragraph. The engine will run like crap without the cat. I never said it would hurt the engine. Can you make an engine run well without major components? Yep. Going back to the OP, it sounds like the question is what would happen with a straight pipe and no other changes.

There is actually. Especially for engines with EGR.

Have you seen a prius header and downpipe? There is a resonator then a straight section with the upstream o2 ... As long as that hasn't been cut out it should have enough back pressure. It will be loud and throw an emissions code but won't run like crap.

Yeah no. Have you seen the EGR system on Prius engine? When the O2 sensor(s) doesn't see what it should, it is going to try to send a lot of exhaust gas back to the intake. That won't happen without back pressure. Air fuel ratio will be off. Will cause sluggish performance and reduced fuel economy. Will also see increased combustion temps that can cause the engine to overheat.

I doubt you’d have an issue with getting part installed but passing inspection might be another story. Good luck with it all!

An aftermarket cat will pass inspection. There is no law which says you need OEM parts.

If you get one installed and get your O2 sensors back on so the check engine light is off and a garage refuses, please report them to the state.

*also, were you to straight pipe until later, your car will not run like shit. It will run a little rich and get a mile or two less a gallon but you will be spewing a lot more emissions into the air.

Someone stole the cats off the bus for the senior center in forestdale. The cats were so expensive to replace that now they are without a way to transport the elderly there and the driver is out of a job. It’s a sad state of affairs

That’s awful.

A garage can most definitely install an aftermarket one. That’s what they’ll most likely use because it’s expensive to get an oem one. Buy it on your own and have them install it to save you some money. Sorry those guys stole yours.