Should I buy new (Flowmaster) cats when having the exhaust replaced? - TCCoA Forums
 
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post #1 of 10 (permalink) Old 04-10-2015, 04:32 PM Thread Starter
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Should I buy new (Flowmaster) cats when having the exhaust replaced?

215k miles on factory cats, no known issue with them, but if I'm replacing everything else should I do these too? I know they clog eventually.

I'm not going to go catless as I don't plan on running mufflers and don't want it to be too loud, nor do I think I can replace the cats with SS pipe on my own.

Let's assume I can get them for $31 each, in which case I might be dumb not to?

http://www.flowmastermufflers.com/?p...category=0&kw=

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post #2 of 10 (permalink) Old 04-10-2015, 06:01 PM
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Stay OEM--they are better in every way. Only exception to that is if they are bad and you must get emission checked.

Think about it OEM convertors are expensive for a reason--the same reason they are stolen. Aftermarkets ones aren't for the same reason.

If all else fails get a bigger hammer!

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post #3 of 10 (permalink) Old 04-10-2015, 06:55 PM
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The cats are needed to pass inspections. So, depending on how rigorous the inspections are, you might need the stock cat. I'd find out what you can get away with at inspections and make your decision based on that.

My stock cats were a very restrictive part of a very restrictive exhaust system. I put on hi-flo 2.5" Magnaflow cats but I don't get inspected.

1992 Tbird LX 5.0, 3.73 gears, 1995 Cobra intake, deleted air silencer, 2.5" mandrel bent dual exhaust, SCP shorty headers. Updated four-hole fuel injectors. SK shift kit in AOD. Vogtland 0.9" springs, Tokico and Bilstein shocks.
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post #4 of 10 (permalink) Old 04-10-2015, 07:00 PM
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post #5 of 10 (permalink) Old 04-11-2015, 07:10 AM
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Quote:
Originally Posted by gordonm1 View Post
The cats are needed to pass inspections. So, depending on how rigorous the inspections are, you might need the stock cat. I'd find out what you can get away with at inspections and make your decision based on that.

My stock cats were a very restrictive part of a very restrictive exhaust system. I put on hi-flo 2.5" Magnaflow cats but I don't get inspected.
They are not as restrictive as every on thinks--now that 90 bend right in front of them is.

If all else fails get a bigger hammer!

93 SC Tbird
MPII w/ Plenum,90mm MAF, 85mm TB, 40# Injectors, 255 lph FP, Double IC w/fan, SCT Chip (Tuned by Jerry),3/4" Raised Top, F52-TT TC, SilverFox AOD 550, SPT-R VB
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post #6 of 10 (permalink) Old 04-11-2015, 11:22 AM
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My 1992 5.0 had a straight pipe that required the 90 degree bend happen in the cat. I'm not really sure what the original poster would do to the front half of the exhaust to improve flow and stay OEM. Bigger pipes with reducers on both ends of all three cats and eliminate the resonator?

You could do the back half first maybe without mufflers or free flow ones Like Magnaflows and see if you are happy. You might find a guy that will reuse the original mufflers and just see what a true dual back half does for you with bigger pipes.

I needed the dual in dual out resonator/xpipe to reduce noise with free flowing rear mufflers. I've still got my original front half and may post a pic here to see how restrictive it looks.

http://i79.photobucket.com/albums/j1...pshlpdefbh.jpg

The newer pipes are the xpipe and 1 nice 90 degree mandrel bend in 2.5". The second exhaust shop that installed the DI/DO resonator and cats only charged another $320. This is what they removed, its a lot bigger and smoother than stock. The passenger side is almost a 90 bend just before the cat and the driver's side that's shielded is a 90 between the cat and down pipe. FYI my entire exhaust system was still solid and could be bolted up to another 1992. It just breathed like it was headed for heart surgery.

1992 Tbird LX 5.0, 3.73 gears, 1995 Cobra intake, deleted air silencer, 2.5" mandrel bent dual exhaust, SCP shorty headers. Updated four-hole fuel injectors. SK shift kit in AOD. Vogtland 0.9" springs, Tokico and Bilstein shocks.

Last edited by gordonm1; 04-11-2015 at 12:19 PM. Reason: add photo
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post #7 of 10 (permalink) Old 04-11-2015, 09:44 PM
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If you're not worried about larger flow in that section, stick with the OEM cats as the larger bodies will do more for sound suppression. Catalytic converters aren't as restrictive as people think they are. The pipes are where you will gain most of the flow. Gradual bends and larger piping(sized appropriately for your application) will flow best. If you're wanting larger pipes up front, then match high flow converters with the right pipe size. The last thing you want is to reduce pipe size down to stock for just the converters and then neck it back up. It creates a bottle neck and hurts flow.

The reason factory converters are stolen is because of the rare Earth metals that are in them like Platinum.

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post #8 of 10 (permalink) Old 04-12-2015, 08:54 AM
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Quote:
Originally Posted by 96MN12Bird View Post

The reason factory converters are stolen is because of the rare Earth metals that are in them like Platinum.
And the amount in OEMs v. Aftermarket is what makes them effective for over 100k miles, while aftermarket are only good for a few years.

If all else fails get a bigger hammer!

93 SC Tbird
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96 1/2 XR7 Sold and Salvaged
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post #9 of 10 (permalink) Old 04-12-2015, 11:56 PM Thread Starter
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No inspections, unless it's done roadside by a trooper who thinks my car is awfully loud!

Not going to have any mufflers, true duals all the way back. The third cat is already long gone.

I was just thinking the factory cats would be nearing the end of their life, but perhaps not.

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post #10 of 10 (permalink) Old 04-14-2015, 09:03 PM
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Quote:
Originally Posted by bowez View Post
And the amount in OEMs v. Aftermarket is what makes them effective for over 100k miles, while aftermarket are only good for a few years.
That's due to the size difference. OEM converters are larger than high flow units. Placement also has a big impact on life.

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