Reinstalling the cat

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528i-1981
Posts: 445
Joined: Wed Feb 07, 2018 5:50 am
Location: Franklin, TN

Reinstalling the cat

Post by 528i-1981 »

Gents, my E12 is currently in TN, which requires emission testing on post 1974 cars. It's for all practical purposes an integrity check, which requires a cat on cars originally equipped with one. The PO of my E12 deleted the cat, which is characterized as "tampering" under TN regs. So, I'm going to have to reinstall a new cat.

My exhaust is non-OEM (i.e., custom) from the manifold back. I like it, but my wife says it's too loud. She drives a rolling library, so that's not surprising.

I'm just starting to look into this but any advice would be welcome. My current exhaust has a very long resonator and relatively free-flow muffler. There won't be room for the cat with my current resonator. Does the cat modulate noise the way a resonator does, or will the car be louder with cat+smaller resonator?

Are there cats that degrade performance less on our cars?

And lastly, am I about to hemorrhage cash on this?
(oo=00=oo) Eric
1981 528i Manual
tlake
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Location: WA

Re: Reinstalling the cat

Post by tlake »

528i-1981 wrote: Sat Apr 24, 2021 7:47 am Gents, my E12 is currently in TN, which requires emission testing on post 1974 cars. It's for all practical purposes an integrity check, which requires a cat on cars originally equipped with one. The PO of my E12 deleted the cat, which is characterized as "tampering" under TN regs. So, I'm going to have to reinstall a new cat.

My exhaust is non-OEM (i.e., custom) from the manifold back. I like it, but my wife says it's too loud. She drives a rolling library, so that's not surprising.

I'm just starting to look into this but any advice would be welcome. My current exhaust has a very long resonator and relatively free-flow muffler. There won't be room for the cat with my current resonator. Does the cat modulate noise the way a resonator does, or will the car be louder with cat+smaller resonator?

Are there cats that degrade performance less on our cars?

And lastly, am I about to hemorrhage cash on this?
Mike W. would be an expert on this, but just to get the ball rolling:

Cat for a classic

But I am thinking since your car has the ECU that recognizes an oxygen sensor, a stock exhaust system would be good. The 1979-81 US 528i has a wire in the harness for the lambda oxygen sensor, with corrective signal going back to the ECU. 8)
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Mike W.
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Re: Reinstalling the cat

Post by Mike W. »

528i-1981 wrote: Sat Apr 24, 2021 7:47 am Gents, my E12 is currently in TN, which requires emission testing on post 1974 cars. It's for all practical purposes an integrity check, which requires a cat on cars originally equipped with one. The PO of my E12 deleted the cat, which is characterized as "tampering" under TN regs. So, I'm going to have to reinstall a new cat.

My exhaust is non-OEM (i.e., custom) from the manifold back. I like it, but my wife says it's too loud. She drives a rolling library, so that's not surprising.

I'm just starting to look into this but any advice would be welcome. My current exhaust has a very long resonator and relatively free-flow muffler. There won't be room for the cat with my current resonator. Does the cat modulate noise the way a resonator does, or will the car be louder with cat+smaller resonator?

Are there cats that degrade performance less on our cars?

And lastly, am I about to hemorrhage cash on this?
With a stock engine, a good quality cat does not affect performance. It has a slight effect on sound, but not as much as a resonator. Price? Not terribly expensive, unless you go the factory route which is the best. There are very inexpensive ones that will only last a year or two at most, or somewhat more expensive OBDII types that last longer, but none as long as the original. Here in California cats need to be specific to the car and have an Executive Order number on them (EO Number) or else it's an automatic fail. Some states back east follow some of Calif's rules so you might want to inquire first.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
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528i-1981
Posts: 445
Joined: Wed Feb 07, 2018 5:50 am
Location: Franklin, TN

Re: Reinstalling the cat

Post by 528i-1981 »

Thanks Mike. I followed tlake's lead which took me to an outfit in the UK (Jetex) that sold the Swedish Redback Classic. At only 10" long (excluding the flanges) it shouldn't be too big of a problem to wedge in. Seems, using the eyeball test, to have good flow-through and is nice and wide. If you flunk in TN, you just have to spend $75 in an attempt to remediate. But that can't include the cost of replacing a cat that was removed by "tampering".

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(oo=00=oo) Eric
1981 528i Manual
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