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Discussion Starter #1
I was wondering who has installed catalytic converters and what you think about them. I'm looking for qualitative feedback on sound reductions, exhaust reductions i.e. smell, overall impression of them, etc. Did you put them on for emissions controls or for some other reason? Do you see any noticable HP change? Would you recommend them? How do they look versus a 4 into 4 without cats? Thanks in advance.
 

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I used them on my MK II, big reduction in noise and was needed for emissions. Did not notice to much HP change, all stock engine. I think the 4 into 4 s' look great and will not use cats this time on my MK III.
 

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Before I built my car, I drove one at relatively low speeds (around 45 mph on New England secondary roads). That car had the same 5.0 donor engine as mine, but straight J-pipes inctead of catalytic converters. After that drive, I was immediately convinced that, for me, the only way to go was with cats to reduce exhaust sound intensity. That's a personal choice of course, but I value my ears. Now that my build is complete (30-mos. now), field tests show I made the right choice. Of course, cats are not the only way to reduce exhaust sounds, but they were an easy one at the time, since I simply added them to my kit order.
Had I not made that decision, I would need to wear ear plugs while driving, and that would be too cumbersome.
Appearance-wise, I believe the difference(between J-pipes, cats, and/or 4 into 4) is unnoticeable. HP-wise, I really don't know. My car has plenty of power (for me), and I am happy. I think one principle applies here to hand-built cars. since we build them the way we think we eill want them in the first place, it really is a small matter to correct or change whatever exhaust system decision you make now, once you take the finished car out and drive it for a while. Give it your best shot and don't worry too much about it for now.
 

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FFCobra Master Craftsman
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Someone posted decibel readings here for a car with and without cats a while back. As I remember, the car with cats at 3,000 RPM was as noisy as a car without cats at 1,000 RPM. Big difference.

I have them and am very happy. The car still has a great rumble but I can actually talk with my passenger when driving at 40 mph with no problem and on the highway with a little effort.
 

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I have cats on mine. I did it for 2 reasons - the stench of unburned HC's and potential emission requirements. It seems now that I don't have to worry about emissions req. with the new 'Replica' law in VA. If you want to hear them, I'm in Warrenton.
 

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Cats for sound reduction. I registered without cats and then added them later to reduce the sound. Would like to try the drags without them but haven't yet. IMO these cars are too loud without cats.
 

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I have cats on my car. I got them because I was going to have to be sniffed for emmisions in Mass, but put them on in my quest for a quieter exhaust. I felt a definite decrease in high rpm horsepower when I put them on. Non quantitative, just seat feel. I've since added a blower and feel they help make power due to the back pressure. My wife won't ride in the car with the straight J pipes, and I have to admit it makes my ears ring after 1/2 hour. I currently run 24" Lobak mufflers, cats and Car Chemistry single disc insert to bring the noise down. I am actively searching for someone with the Quiet Pipes to see how they sound and will probably get them if they are quiet enough. No joke, if you've increased the power the bark hurts!
 

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The inspection station I went to at the time I finished the car (in 1999) said not to bother coming over for inspection without cats installed (Massachusetts). Originally I had straight Jpipes on. When I put the cats on, the sound got much less "edgy" and really cool-sounding. This probably means the cats dropped the high frequency part of the sound. All I can say is that the car sounds powerful and authoritative and not-obnoxious. Most humans really love the sound, including me. I have a 1993 5.0 with Ford E-cam, Cobra intake, BBK headers, bigger intake path (mass flow meter and throttle body). Engine experts say it's about 280HP.
 

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Just keep a close eye on the welds. I had cats on mine. Actually had been welded once already. Cracked again. You need to make some kind of bracket for them up front to take the weight of the pipes off....

I did like the sound better with the cats but they are very restrictive with a Supercharger like I have. I noticed a kick in the pants with just the J-pipes after changing over. I think I might just try the CC inserts and go from there.



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I ran cats for about 5 years, to pass CA emissions and to be friendly to the neighbors and my ears. The cats takes the raspy pitchy sound out, but keeps the rumble. I've been running without the cats for the past few years and I've grown acustom to them. I do think they take the HP down some, but with a strong V8 and a 2000 lb car, you can spare a few HP.
 

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Discussion Starter #11
Thanks for the responses. Can anyone else provide some feedback? I don't have the kit yet so I can't compare exhaust notes or smells one way or another. It seems like people enjoyed the benefits that the cats provided. I want to be able to enjoy the car (and I want my passengers to enjoy it too) without going deaf or smelling bad. Otherwise no one will want to ride!
 

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Chef...see if you can find a few near you to get an idea first hand. It really is personal choice and loud exhaust to someone is sweet music to others.
 

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I run cats and on the interstate and the wind and tire noise is greater than the exhaust noise. Still sounds off if you "floor it". 22K miles and holding up fine.
 
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