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Cat removal pros and cons on a mostly-track car

 
Old 08-28-2016, 10:38 PM
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Default Cat removal pros and cons on a mostly-track car

My 968 is no longer required to have its emissions tested in the state of Texas, since it is now over 25 years old. It's primarily a track car - I only drive it on the street to get to and from the track, so I'm wondering if there would be any benefit, other than shedding a few pounds, to replacing the catalytic converter with a straight pipe. I have an RS Barn cat back exhaust, with no resonator. The engine is pretty much stock. One benefit I can think of is that since the cats are NLA, removing it would preserve it in case I ever have to have the car emissions tested in the future, e.g. if I move to a state that requires it. Thanks.
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Old 08-29-2016, 11:54 AM
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Originally Posted by Cloud9...68 View Post
My 968 is no longer required to have its emissions tested in the state of Texas, since it is now over 25 years old. It's primarily a track car - I only drive it on the street to get to and from the track, so I'm wondering if there would be any benefit, other than shedding a few pounds, to replacing the catalytic converter with a straight pipe. I have an RS Barn cat back exhaust, with no resonator. The engine is pretty much stock. One benefit I can think of is that since the cats are NLA, removing it would preserve it in case I ever have to have the car emissions tested in the future, e.g. if I move to a state that requires it. Thanks.
I will see if I can find the dyno charts, but ones I have seen with before after, same car, you will lose power, if you remove the cat, I believe primarily torque.

What is that saying, HP sells cars, Torque wins races?
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Old 08-29-2016, 08:25 PM
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Yeah, I seem to remember that as well. Exhaust mods are very tricky - removing restriction to gas flow doesn't necessarily always translate to increased power. If that's the consensus, I guess I'll leave the cat in place. Thanks.
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Old 08-29-2016, 11:07 PM
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It seems so counter intuitive to remove an exhaust restriction and actually lose power. I find it a little difficult to believe but what do I know?
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Old 08-30-2016, 07:22 AM
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I would replace it with a resonator pipe, like a magnaflow.

You will likely gain power up top where it matters for a track car.
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Old 08-31-2016, 12:36 PM
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You don't want to lose back pressure from removing restriction from the exhaust, loses low end torque. MagnaFlow is the muffler Pete supplies with his system so that's likely a very good source for a replacement pipe as Eric suggested. Maybe check with Pete on a recommendation for his system? I would try to save the cat for possible future use. I live in a county without smog testing, maybe I will do the same, let us know what Pete says.
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Old 08-31-2016, 01:12 PM
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I must be crazy, because a few months ago I put an OEM one back in I had an aftermarket cat from the PO, car is much quieter now, but it was a nice and loud one before with the BB exhaust I have. Lucky for me I can bolt it back in or out. One day would like to do some runs.

Butt dyno says it feels like I have more torque when rolling into curves and accelerating from the apex.
I usually hang around the 4k RPM mark. This is after driving the car for 2 years with the Aftermarket Cat. I also probably added about 20lbs to the car too by doing this.

Anyways, butt dyno says nothing and it means nothing. You should do a before and after dyno run on the same dyno, all things being equal.
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Old 09-01-2016, 05:21 PM
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You won't "lose "anything. Just changes the HP/ torque curve.
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Old 09-02-2016, 08:37 PM
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Originally Posted by joes View Post
You won't "lose "anything. Just changes the HP/ torque curve.
That makes sense. The consensus seems to be that reducing restriction by removing the cat increases top end power a little in exchange for a loss of some low end torque. I try to keep it between 4000 and 6500 rpm on the track, so it seems that removing the cat would be a small net gain.
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