To Cat or Not to Cat??

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Both the no cats and high flow cats will add some HP to your 99. With cats figure 7-10 hp gain. Without cats figure 12-15 hp gain. Don't know where you live, so if emission testing is being done it will be a problem if you go with offroads. The ones with cats will pass the sniffer test.

If you go without the cats, you will get a MIL. You'll need to get what are called MIL eliminators. Fakes the computer into thing you have cats. You can get them from Dallas Mustang or TRZ for something like $60.

Hope this helps a little.