ATL CAT By pass

Roswell · 05-23-2017, 02:42 PM

I am trying to decide on a Cat bypass pipe or leaving the original CAT in place. My only concern with the CAT bypass is the increase in loudness of the exhaust. Replacing the original muffler with a Monty. Any Atlanta forum member in the North ATL / Roswell / Alpharetta area with a CAT bypass set up willing to meet and let me hear the difference? I am available throughout the day this week.

Thanks!!

Bob Kontak · Bob Kontak's Garage

Just a data point...........

I put the Fabspeed Euro pre muffler on my 81 SC. It's a fancy name for a cat bypass. Also ran the Bursch (pretty sure it was Bursch) cat bypass test pipe for years. Just a collector with an empty tube and an O2 bung.

Neither made any "write home about" difference noise wise.

I did buy and gut a fairly pristine 3.2 muffler and throw it on. That was loud and frankly the SC did not have the stones to make it sound rich at higher RPM's. It sounded boy racer above 5,000 RPM's.

It sounded great at low RPM's, really great, but there was only minor baffling in the Fabspeed. Otherwise, open tubes.

I say try the Monty muffler without messing with cat first.

Roswell · 05-23-2017, 05:13 PM

Bob - Thank you for the feedback. At this point I am leaning towards staying with the original CAT

Van

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by Roswell

Bob - Thank you for the feedback. At this point I am leaning towards staying with the original CAT

No downside to that. Mine was rattly when shaken. The honeycomb was degrading.

They are pretty fat cats. Lots of room for flow.

Would be nice to find a pal though with close to the same set up for a listen. Good luck.

Stutzdriver · Stutzdriver's Garage

I just removed the cat and the muffler on my 84 Carrera as the origiNaL bolts on the flanges had disintegrated to the point I was afraid they might fail at some in opportune point. Had to cut off the bolt heads and use every trick in the book to remove the bolts (guess I shouldn't have worried about it coming apart.

I considered gutting the cat but i put it together as it was. The original cat is no longer available and i saw the used cat prices and decided to leave it intact, the car has under 67,000 miles so this cat has a long life left.

Now that it was apart once it will be easier next time. I would like to upgrade the muffler but that's for another day. I am in the exhaust business and can come up with lots of options so I'll have to look at a later date.

Arne2 · Arne2's Garage

I have driven my '84 with both a factory cat and a M&K premuffler. No difference n sound. I strongly suspect a true bypass (plain pipe) would be louder.

nene · nene's Garage

I just installed a straight bypass and really enjoy the faint deep throaty sound. Really happy with it.

Flojo · Flojo's Garage

is keeping the CAT a must?

if not, do yourself a little-pre-x-mas and get yourself SSIs 2in1.
the CAt sensor is deletable for your 84.

I do not regret these SSI on my SC any minute!

jlex · jlex's Garage

Quote:

Originally Posted by Roswell

Bob - Thank you for the feedback. At this point I am leaning towards staying with the original CAT

Van

At least it won't stink...

tirwin · tirwin's Garage

Hey, Roswell -

I live close by. I have a test pipe with a 1-in/2-out muffler on my '83. It's definitely louder than stock but not obnoxious.

I also have a cat that is gutted laying on the floor of my garage right now. I think it should bolt right up to your car. You're welcome to borrow it if you'd like to try it on your car.

Jesse16 · Jesse16's Garage

87 and removed my melted, damaged cat several years ago (no emmission here) and replaced first with a straight pipe from MK and later with their pre-muffler version. Both are louder, pre-muffler maybe slightly less. Bit cleaner look underneath if you care. M&K told me this would be the result and they were correct. I"m still happy, car sounds pretty good.

mderienzo · 05-24-2017, 05:48 AM

Quote:

Originally Posted by nene

I just installed a straight bypass and really enjoy the faint deep throaty sound. Really happy with it.

Same here on my '82 SC. Sound seems just right to me with a stock Carrera 3.2 muffler and straight bypass (M&K). Another advantage of removing the cat is eliminating a major source of heat under the car, especially when sitting in traffic and after the car is parked.

Mark