Cat bypass vs empty cat

[Amstaff]

what is the real difference between running a cat bypass and just clearing out the existing cat converter?

Any real horsepower loss or gain?

I have a 3.0 in a 1972 and want to pull the headers and run the stock exhaust but don't want to lose a lot of horsepower.

Thanks

[tratza]

No idea. I switched mine out to remove some heat on the engine (lived in "Houmidston" at the time) and a little weight. Sound was better. Very low. I'm guessing there would be no benefit without intake improvements. May even lose some low end.

[Amstaff]

The motor has 964 cams and Webers on it. Currently has headers to a 2 in 2 out exhaust.

[racerr1958]

I went from a gutted cat pipe to a fab speed cat bypass. There was no noticeable performance change that I could distinguish. I was not expecting anything measurable anyway.
The sound did change, it became a little bit raspier with the new pipe.

[Quicksilver]

CAT vs no CAT generally doesn't give you a performance boost unless it was a really old style (unlikely) or unless the engine was retuned to deal with the change in the induction. Most improvement people report is actually the natural tendency to hear the louder noise and think they are making more power.
Unless you measure it it almost certainly your brain lying to you.

[Amstaff]

So how do you gut a cat? (Pun intended)

[merlinfe]

Amstaff,

I can tell you about what's happened in reverse on a 3.0L. I went through a number of phases with the exhaust on my 911SC.

I first replaced the cat with a Euro premuffler. Lost some torque in the low end but the engine was more free to rev to redline. Flat spot above 5500rpm shifted right to around 6000rpm.

Next I went with an M&K GT3 style 1in2out muffler. More toque lost on the low end, louder on the upper RPM band, but no power band change other wise.

Then I went with SSIs and a 2in2out GT3 Dansk muffler. Toque curve is flat from 2200rpm to redline when flooring it.

In your case with a return to a stock SC heat exchanger set up I would expect an increase in low end torque with a flat spot above 5500rpm with a stock banana type muffler. Your going to feel a noticeable difference in the car.

I would try what you want, but don't sell your old stuff until your happy with the new stuff.

-Steve.

[JoshCole1122]

Originally Posted by Amstaff

So how do you gut a cat? (Pun intended)

Using a large pipe or screw driver and rubber mallet hammer all of the honeycomb emissions catching material out of the pipe. keep chiseling away until the interior pipe is completely clean.

[JoshCole1122]

good article explaining exhaust pipe sizes related to power.

Header Basics - How Headers Contribute to Horsepower - Hot Rod Network

[RarlyL8]

The 3.0L SC engine responds best to 1.5" primary headers and a free flowing dual inlet muffler.
There is a bigger gain with the Carrera using a premuffler than with the SC.

[Jherriott]

I have had both, but I didn't notice anything different. It would be a weight savings and perhaps a more laminar flow with the Fabspeed bypass.

Jase.

[RarlyL8]

Don't pull the headers on your 3.0L, that engine responds very well to 1.5" primary headers and a good flowing muffler. Why are you wanting to go back to the stock exchangers?