Does a Cat bypass make a big difference in loudness?
 

I have an 87 3.2 that I recently just installed a B&B cat back exhaust on, been happy with the product, easy to install with nice fitment. I also bought an M&K cat bypass pipe but haven't installed that yet, the car already has an aftermarket cat that is much smaller and I would assume much less restrictive then stock. My question is, is it worth installing the Cat bypass pipe? Will I notice a louder exhaust note? I am concerned that without the cat the car will stink and being that its a convertible I don't want to deal with that. Any help with this would be greatly appreciated.

Thank you!

87 here - replaced my stock Porsche cat/muffler with Dansk pipe and Dansk sport muffler from our host. To be honest, doesn't sound that much different, maybe a deeper tone but not loud by any means. Have not noticed the much discussed "stink".....at all.

It made it significantly louder on my 3.0 I had a straight through glass pack for the muffler and after I put the bypass on it was too loud so I had to make a regular muffler for it. I cant speak for the stink It was so long ago I dont remember. Usually I prefer the exhaust smell without a cat I guess its personal preference.

From a power perspective our MKM60 Cat Bypass and MKM32 Premufflers will add about 15hp over a catalytic converter. The sound level is different, the MKM60 being a straight pipe while the MKM32 is an actual muffler. Final sound and level is determined by the main muffler you have. It will be louder than it is now but not tremendously.
It is not uncommon to experience the "stink" of a rich exhaust when exchanging a catalytic converter for a premuffler or bypass pipe. This is typically due to the mixture being out of spec. The catalytic converter will mask the odor where the others do not. Adjust the mixture and the smell goes away.

1987 here also. I exchanged the cat for a Bursch bypass 20 years ago. Sound was definitely deeper which the wife even liked. Later cut a hole on the right side of the stock muffler after changing the cams during a rebuild and was significantly louder but no drown (sp) and the wife still liked it. She drives a new BMW 5 series hybrid which is really quiet so go figure why I get no complaints from the chief.

+1 rich = stink without a cat.

I very recently replaced my cat with the Fabspeed cat bypass (has glass resonator). Made a significant improvement in torque and the sound is great. Just a bit louder and throughtier so you know there is something extra under the hood.

Car seemed to run a bit lean with the cat bypass and stock chip. installed the SW chip and it's extremely smooth now.

Over all the cat bypass made a significant difference in performance. Car just runs easier now. A little louder but in a good way.

Chris
89 Carrera

I installed the B&B cat back muffler and it made a huge difference in mid range performance, just on the fence about installing the cat bypass, I have it i guess i should try it and see what it does. I can always change it back if it bothers me.

Thanks for the input everyone!

The MKM60 Cat Bypass pipe will make a noticeable difference. Look at the size of the inlets, the smooth merge and the ID as compared to whatever you have on now. The only possible drawback might be sound level, if the final muffler is a loud one it will be a bit louder on the pipe.

I would prefer to get some more sound out of it, i have found that the B&B is not very loud, its a bit more throaty than stock but not much louder, I have mostly noticed mid range performance gains. I will put on the cat bypass and try it out!

I also replaced my cat with the Fabspeed cat bypass. Made a noticeable improvement in torque and the sound is great. Somewhat louder and deeper (throatier) but pleasing to be sure. running a SW chip and M&K 2 into 1 muffler helps. My experience is that the bypass does make a seat in the pants change in mid-range and only more volume in a pleasing way.