Comment by Alupis
5 years ago
> A cheap generic cat might have the bare minimum amount of catalyst, and might not do a very good job
It depends on the car/engine. My old Mazda RX-8 had a huge cat - longer than the muffler and cost me $2,000 to replace (including labor) back in the late 2000's.
The rotary engine in that vehicle had a terribly difficult time passing California's emission laws even when it was brand new off the lot - which led to strange "hacks" including a blower motor that moved high volumes of air through the exhaust to heat the cat sooner and somehow improve it's numbers, among other things. I assume the extra-long cat was part of the shenanigans Mazda had to go through to get it compliant.
> moved high volumes of air through the exhaust to heat the cat sooner and somehow improve it's numbers
This is because the catalyst works more efficiently at higher temperatures. Emission regs also test vehicles under a cold start. The quicker the cat can be heated up, the quicker it starts working, and that equals fewer total emissions over a given period of operation.
It's funny you mention the RX-8, since I'm in the (slow) process of converting one to electric. That weird cat blower was one of the many parts I removed while thinking "I'm glad I don't have to understand or care about why this car needed something like that in the first place".
Just talking about the RX-8 brings back great memories - what a strange, yet beautiful car!
The cat blower, and the subtle whining sound it made when you started up cold was one of the ways every RX-8 owner was hazed into the fold... after calling the dealer or posting on a forum and finding out it's entirely normal!
Other oddities included how it deliberately burned oil (scaring new owners into thinking they had a serious engine problem), and how you were required to drive it hard to clear out its engine ports (multiple Mazda mechanics confirmed this factoid) - driving it like a normal car would literally clog up the exhaust ports and cause a loss of power (something to do with the lack of moving valves). If memory serves right, it had only 3 (!!!) moving parts in the engine, and was perfectly content to hang out at 9,000 RPM all day - that's incredible.
But, it seems the issues Mazda had maintaining it's emission certifications, and warranty issues with those apex seals (mine had 3 engine replacements over it's lifetime) eventually caused it to be retired. I was sad back then, and still sad we don't have a new improved version - there's really nothing else quite like it out there, not even the RX-7. It really was/is an enthusiast's car.
Good luck on your project - sounds like a fun one!
I'm hoping LiquidPiston's rotary engine design pans out: https://news.ycombinator.com/item?id=25450477
In theory, it should fix some of the maintenance issues (apex seals are attached to a stationary part of the engine where they can be more easily lubricated) and fuel efficiency / emissions issues (combustion chamber is closer to spherical).
I like the idea of the Mazda rotary engine, but I'm not really surprised they stopped making them, due to fuel economy and emissions. And at them moment, the hundred-thousand mile engine rebuild interval basically means you can get an RX-8 with a bad engine for almost nothing, which opens up a nice opportunity for EV conversion. It's hard to imagine a nicer platform to start from.
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