C4 front cats
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Joined: Jan 2024
Posts: 87
Likes: 28
From: New Hampshire
C4 front cats
Hey everyone,
I ventured over from the C6 forums since I bought my kid a 1989 Corvette Convertible. The car has an exhaust leak as the old owner stated he believes the exhaust manifold to midpipe has broken studs. He did include a replacement OEM midpipe with cats but we just found one of the cat internals is missing. So that pipe is no good.
I don’t know what’s on the car currently but I noticed many aftermarket midpipe don’t include front cats and seem to only utilize the one cat after the y-pipe merge.
my question is how does no front cats affect the car? I’m not up to date on older OBD1 cars. Trying to run a close to stock car as possible but if the car runs fine without the front cats then I will leave them out with the purchase of a new midpipe.
thanks,
Derrick
I ventured over from the C6 forums since I bought my kid a 1989 Corvette Convertible. The car has an exhaust leak as the old owner stated he believes the exhaust manifold to midpipe has broken studs. He did include a replacement OEM midpipe with cats but we just found one of the cat internals is missing. So that pipe is no good.
I don’t know what’s on the car currently but I noticed many aftermarket midpipe don’t include front cats and seem to only utilize the one cat after the y-pipe merge.
my question is how does no front cats affect the car? I’m not up to date on older OBD1 cars. Trying to run a close to stock car as possible but if the car runs fine without the front cats then I will leave them out with the purchase of a new midpipe.
thanks,
Derrick
Melting Slicks
Joined: Nov 2016
Posts: 2,256
Likes: 3,082
From: So Cal
2023 C4 of the Year Finalist - Unmodified
I don’t know what’s on the car currently but I noticed many aftermarket midpipe don’t include front cats and seem to only utilize the one cat after the y-pipe merge. My question is how does no front cats affect the car? Trying to run a close to stock car as possible but if the car runs fine without the front cats then I will leave them out with the purchase of a new midpipe.
Anecdotal: I owned a 1988 convertible automatic from 1995 to 1998. I live in SoCal so it had to pass emissions. During my ownership the front cats developed rattles. I obtained a no-cat head-pipe and installed it. The car still passed California emissions with no problems or changes. I don't recall any differences in 'performance'. There may have been subtle changes in the exhaust note and the 'ring' of the head-pipes without the cats, but no biggie. Basically, neither I nor the car knew the difference. Cheers.
Racer
Joined: Oct 2012
Posts: 311
Likes: 128
As I understand it, the front pre-cats are there to clean the exhaust during warm-up only. Once the car is up to temp, the main cat takes over the work. I presume the fronts have a different formulation to accomplish this but I don't know for sure.
I can tell you that I recently replaced the main cat on my '89 with a magnaflow cat and since my front pre-cats are gutted (only by necessity, as they were already busted up inside) I failed an emissions test when I had to wait in a super long line because the main cat's temp wasn't high enough when I got to the station and it wasn't even working.
When I went back for another go, I made sure to keep my revs up while waiting in line and this worked; I sailed through. With functioning pre-cats, I probably would have passed the first one.
I can tell you that I recently replaced the main cat on my '89 with a magnaflow cat and since my front pre-cats are gutted (only by necessity, as they were already busted up inside) I failed an emissions test when I had to wait in a super long line because the main cat's temp wasn't high enough when I got to the station and it wasn't even working.
When I went back for another go, I made sure to keep my revs up while waiting in line and this worked; I sailed through. With functioning pre-cats, I probably would have passed the first one.
