Is my cat a pipe?

[shawn908]

I have the car on jack stands to get to some projects, one of which required removal of the exhaust. Was thinking before I reassemble, consider removal of the catalytic converter, replace with an M&K pre-muffler and also replace with a lighter weight M&K single in/out (I like reducing the weight of the car). As shown, the rust on the cat is serious, and I've been using a sawzall to attempt to cut off bolt heads. Not much room so thinking about getting a dremel with a cut off wheel for better access. Any other suggestions welcome on how to remove the bolts rust-welded to the cat.

Second photo shows a colonoscopy-like view of the "catalytic converter". Which begs the question: is my cat a pipe? Looks like it has been gutted. The white tab is the oxygen sensor (the photo rotated 90 degrees). Now thinking about getting the M&K bypass pipe rather than the pre-muffler. Looking at the inside of the cat, would it be correct that a bypass pipe would be no louder than the cat on the car now?

Suppose I could leave as is, but the rusty mess compels me to replace the "cat" with something.

[smadsen]

If that's the colonoscopy of your cat, the ceramic bricks have been broken out and removed, leaving you with pretty much a straight pipe. By the looks of the nut/bolt hardware it's been that way a while.

New cat from our host is around $450.

Most OEM units time out around 150,000 miles, so the odds of purchasing a used 30-40 year old unit in working order are nil.

We could argue for days about whether or not your car requires the back pressure provided by the cat. I don't know about EPA compliance in your state, the car will run O.K. with your non-cat or a better looking after market straight pipe (test pipe), but the foolproof fix is a new replacement cat.

[David Inc.]

It's fun running with a test pipe for a little more noise, but until you really change out the exhaust it's not so much more entertaining.

Besides, without a cat in place you'll notice pretty quickly that running the engine in the garage is a very bad idea. "Okay I'll just run her for a bit to check something and man why does my head hurt so bad all of a sudden?"

[darrin]

other than beautification, nothing really to be gained with a test pipe or premuffler if there are no leaks in your current hollowed cat -- dremel off the bolts and remount with new hardware and your "cat" will continue to serve you

If you do want to change things up, recommend checking out M&K's active exhaust premuffler -- have the cat version on my targa and really enjoy both the sound and the butt dyno bump when the muffler bypass valve opens up.

[Teutonics]

Bypass the dremel and go for a die grinder with cutoff wheel or oscilating tool with metal cutting blade. Dremel will take forever...

I'm not sure if this is still an option, but many years ago I purchased an OEM European pre-muffler. Maybe the inspection guys around here aren't as smart or diligent, but I've never had it questioned during emissions (since it looks factory). I didn't notice any significant noise or performance changes, but figured since it was delivered as new outside of US it had to be as good as or better than the test pipe that was on the car when purchased and gutted cat that came with the car to be switched out for every inspection. :-/

[tirwin]

I found the same thing when I first bought my car -- cat had been hollowed out. I have zero scientific data to prove this but I personally believe the car runs worse with a hollowed out cat.

My personal opinion is use something that was designed for the job -- either use an actual cat, a test pipe or a premuffler. I suspect there is something about the turbulence of the exhaust gases expanding into the big chamber of a hollowed out cat and then being reduced again on their way to the muffler that is no bueno.

I bought a used test pipe and it was an improvement to me. I've always wondered if anyone has every taken the time to study this... but why would you?

Long story short, I'm currently running a Magnaflow cat with O2 bung and a 1-in/2-out exhaust. I'm getting headers and 2-in/2-out from Brian at M&K. The cat and the old test pipe will be for sale soon. The cat is a 49-state and has about 1000 miles on it. PM me if interested.

[Snitzler]

I have a M&K single in/out with the pre-muffler. It sounds great and it sure doesn't weigh much. I bought the car with the exhaust system installed so I can't quantify the weight savings. I was doing some work on the heater and I took a picture inside the M&K pre-muffler. Looks similar and you can see the O2 sensor. My suggestion is to cut off the fasteners and install new ones. Then buy the M&k!

[pampadori]

You'd smell a lot better if you put an actual cat back on. But for a toy sports car which most of us have, the desire for the last fraction of a horsepower is too strong. seriously consider a cat if you don't desire that. There are already enough jerks like myself without a cat destroying the planet.

[SilverWT]

Just for the hell of it, here is a view down the end of a stock Euro pre muffler. Externally it has the same case as a cat, but internally just straight through with some perforated baffles.

Mark

[Storage Man]

Getting rid of the cat saves weight, reduces heat, and improves flow.
I have the M&K pre muffler in place of the cat w/ the stock muffler. Yes, the smell ain't great but prefer the pre muffler to the pipe due to the reduced crackle/chirp in the exhaust tone with the stock muffler.

[tirwin]

Well, there is one other point... if you’re running high ZDDP oil it will accelerate the demise of the catalyst. Good reason to go cat-free. Or to move out of California.

[Pigeye]

I removed my cat. The bolts looked like yours or worse. Used a Dremel with flexible extension and many little cutoff wheels. Angle grinders don’t fit / even my pneumatic little one was too big in some spots. Also, had to use a pneumatic air chisel w/ pointy end to get the bolts out once cut off as they were rusted/welded on. Replaced all the hardware, used copper anti seize and intend one replacing the hardware this year or at least unbolting and rebolting (2 years) - it was a weekend.

[Storage Man]

Originally Posted by tirwin

Well, there is one other point... if you’re running high ZDDP oil it will accelerate the demise of the catalyst. Good reason to go cat-free. Or to move out of California.

Completely forgot that also!

[shawn908]

Thanks all - the responses here resonate for me on this problem...
The views into the pipe also clearly show a difference in the functional diameter of the "cat" on my car vs an engineered alternative - suppose if a large diameter empty tube with irregular interior surfaces was an optimal choice for exhaust gas bypass pipes/test pipes would look different.
The Sawzall is just too big to get at more than one bolt head - not feasible as a tool here. I looked into a cut off wheel but after 5 or 6 YouTube videos - agree with Pigeye - I think these may end up being be too large for the tight spaces. If a Dremel has worked - I will stop by the local hardware store (shop local) wearing a mask and see what they have in stock. And buy several cutoff wheels.

tirwin - I do use a ZDDP - Joe Gibbs - so good to know about effect on a cat. More reason to go bypass pipe. Thanks also for the offer on the test pipe - for once.... I am going to buy new and get both from M&K.

I like the description of the bypass on M&K site re: potential performance increase - but if the bypass pipe and the single in/out is louder and lighter its a win for me. Another weekend under the 911 approaches.

[Mark Salvetti]

The small Dremel shouldn't take too long. Cut a vertical slot through the nut, then with a chisel in the slot and a hammer you should be able to knock off the nut.

Since you don't need to save the bolt, you can be pretty aggressive.

Mark

[RarlyL8]

A gutted out cat is pretty much a flow disaster. Go for something with smooth transitions and a static smooth ID such as an M&K Bypass pipes have no muffling ability, if the system is a little loud for you now a pre-muffler would help. Often times removing the cat results in exhaust smell at cold start. This is an indication of two things, one is the cat was working and two being you need a tune up. EFI controlled engines should not smell more than just a hint at cold start, same as early CIS cars that have no cat. Over time the mixture goes rich injectors start to leak spark plugs and wires age and generally everything performs sub-par. Fix all that and the start up smell is vastly reduced.

[Pigeye]

Originally Posted by Mark Salvetti

The small Dremel shouldn't take too long. Cut a vertical slot through the nut, then with a chisel in the slot and a hammer you should be able to knock off the nut.

Since you don't need to save the bolt, you can be pretty aggressive.

Mark

^ this - also, I’d go ahead and get that flexible head for the dremel, if they have. You can always return it. Mine would have taken a lot longer w/o it. Maybe I just had less body flexibility. Ha ha

[911SauCy]

Opinion: If you're worried about the smell...you have the wrong car. If you're concerned about a cat for clean air and "saving the planet"...you have the wrong car.

Stock cat and stock muffler are very heavy compared to the M&K products. Mine were sold, why someone besides a scrap yard would want them, beyond me.

For weight savings, performance, and a great sound I'd go straight-pipe in place of cat and the M&K muffler you're considering.

Will it smell a little on cold start, yep! That's part of the experience.

4" cut off wheel carefully placed will get the job done quickest, Dremel will work but be prepared to pack your patience

[Cevan]

Originally Posted by David Inc.

It's fun running with a test pipe for a little more noise, but until you really change out the exhaust it's not so much more entertaining.

Besides, without a cat in place you'll notice pretty quickly that running the engine in the garage is a very bad idea. "Okay I'll just run her for a bit to check something and man why does my head hurt so bad all of a sudden?"

I don't know. I replaced my M&K premuffler with a test pipe I was given and definitely sounds better at cold start and idle. Now my beautiful premuffler sits on a shelf in all its stainless steel glory.

[tirwin]

Think of the cat/test pipe/premuffler + muffler as combinations. Some are better or worse depending on everyone’s subjective preferences and budget.

I love the raw sound of my 2-in/1-out with the test pipe. When I fired the car up at gatherings I always get a big thumbs up. It was over 90dB at idle though. After 5-6 hours on road trips in the car I was mentally exhausted. (ha! see what I did there!)

I tried putting a cat back on and it knocked it down some, but not enough. Mid 80s. My entirely non-scientific study with a statistical sample of 1 suggests that the car/test pipe/prefmuffler variable is worth around 10dB difference in the equation, give or take.