Advantages/Disadvantages to hollowing out cat

[LCOX]

The cat converter on my 911 is plugged up and needs replacing.
There is no smog testing here during state inspection. Considering hollowing out my cat rather than buying a new unit.

Advantages/Disadvantages to doing this? Im sure alot more disadvantages.

[jlex]

One thing for sure, the exhaust will stink like a pre-cat car. Would probably sound better, though.

[dicklague]

Originally Posted by jlex

One thing for sure, the exhaust will stink like a pre-cat car. Would probably sound better, though.

STINK!!! Porsche hydrocarbon perfume........just like that VW!!

[KNS]

I've run an SC and a Carrera without a Cat, neither one of them caused a stink. Not sure where that claim comes from.

[Antomero]

3.2 Scart exhaust with Scart pre muffler no stink.
Just Great melody

[Matt Monson]

Just buy a cat bypass and bolt it in.

[sparkysvega]

I second the cat bypass.

[HarryD]

Your dead cat is worth money. Get a bypass pipe and sell the dead cat to a recycler.

[Noah930]

Originally Posted by KNS

I've run an SC and a Carrera without a Cat, neither one of them caused a stink. Not sure where that claim comes from.

Through the local canyons I have followed a friend (many times) who only bolts in his cat for bienniel smogging. I can smell him clearly.

[RarlyL8]

Heavy exhaust smell after removing a cat can typically be remedied by tuning up the engine and mixture setting. Catalytic converters cover this up as the engine ages. A well tuned SC or Carrera will not stink badly after cold start. Gutting a cat reduces back pressure but that's about it. The result is not a nice smooth path of flow for the exhaust. If looking for performance best to get a piece that is properly designed for that function. I think I know a guy that can hook you up.

[porsche930dude]

a bypass pipe / pre muffler allows for more room to valve adjust . Im not sure how much a bypass goes for these days but recycling the cat will likely pay for most of it. I kept mine as it was still good but who knows when the state might decide you need one again. As for the smell I prefer the smell without than the nasty stench a cat puts off. I wouldnt hollow it out. Its just a very teenagerish thing to do. Not on a porsche anyway. I know this because i did it when i was a teenager

[slow&rusty]

No cat, no problem, no smell but more hers-purr-wers.

[bkreigsr]

FWIW, the salvage yards around here are buying cats for $75.

[shadowjack1]

A hollow cat is still a big heat producer. GO with the bypass pipe.

[darrin]

My vote is to splurge and get the M&K active exhaust -- https://mkexhaust.com/active-exhaust-with-pre-muffler/ -- the cat version transformed my car (when at/towards WOT, I appreciate both the additional kick and aural pleasure produced by the open(ing) bypass valve and would expect the non-cat version to do more-so with both.

[87maniac]

Will the M&K active exhaust pass CA smog test?

[RarlyL8]

Any cat or pre-muffler can be plugged into the active exhaust. We have a CARB approved cat that is used for those in CA.

[eastbay]

"There is no smog testing here during state inspection"
SSIs and matching muffler for sure then. Surprised no one mentioned it.

[911SauCy]

Bypass pipe all day long.

Cat is heavy and there's no point of ruining a good cat when a bypass is like $250.

The car will smell, how it's supposed to smell.

[famoroso]

I've run hollowed factory cat on a 3.2. I like that it appeared as stock. I consider it a "stealth bypass." Car ran STRONG (albeit it also had an open air box, Web 20/21 cams, Dansk 84mm Sport muffler and a Steve Wong dyno tune)...



Stock cat weighs 13.85 lbs.



Gutted stock cat weighs 10.21 lbs.



I run an M&K Active Exhaust pre-muffler on my 3.4. It weighs 8.75 lbs. I have yet to dyno tune / test this engine.



Yes, I have a problem...