cat/no cat hp difference?
 

I am planning on aftermarket headers soon (not sure which one yet). What is the approximate hp/sound difference,if any, between having a cat or not having one?

If you're running turbo it'll make a big difference. If you get headers I would get catless because you have a second cat one on the front pipe. No check engine light and it doesn't stink up the cabin either.

N/A Autox car/DD/Occasional track days

Front pipe cat doesn't matter. Both O2 sensors are pre-post cat in the header. Just tune it and you'll be good.

You aren't leaving any notable HP on the table by going catless vs catted. Catless is cheaper, but possibly raspier.

I dynoed with and without a cat. It was about a 4 hp difference.

Marginal difference. I previous had zero cat's on my setup. Exhaust is slightly louder and raspier. I only changed because of the SMELL and poisonous gas in the garage whenever I let the car warm up in the mornings. Not worth the extra 3-4hp gain for catless.

Plus you can SMELL it while sitting at the traffic lights with your windows down too, a copper just needs to sniff it with his snout and then you'll get pulled over and defected for that. Not worth it.

I have to keep the one the rear cat per scca stx regulations

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