altarchsa

Why is it necessary to buy an expensive ($300=/-) cat bypass test pipe? Can't the guts of the OEM cat be punched out and cleaned up?

It appears to be metal, as compared to the ceramic core I encountered on an old Jeep Grand Cherokee. But I just punched the core until it broke, then cleaned it up Why not the same with the Pcar cat core?

Oracle

I think you want to keep the CAT in case you need to smog the car and will be near impossible to sell a smelly car due to no CAT. Also the guts are really toxic so dispose the them in the regular garbage is not good. Probably is illegal to sell a car with the CAT removed in some states when it came with it from the factory...

ThomasC2

Yes, this is why. the functionality is no different.

darth

You can sell the precious metals inside the cat that you punch out. Up here thieves have been cutting off catalytic convertors on parked cars for the precious metals inside to scrap yards or auto recyclers who resell them at a drastically lreduced price compared to a new cat. I know when my 78 Ford needed new dual cats because the old ones rotted out, Ford wanted upwards of a thousand doallars a piece for them (i.e. more than what the car is worth), I went with $400 dollar (i.e. still more than what the car is worth to someone else other than me as it was good transportation) knock offs that Speedy mufler sold. The money you get from scrap yard can go towards a proper bypass pipe. Be sure you wear a proper mask if you decide to punch them out as 3-nitrobenzanthrone and dinitropyrene, are highly toxic (i.e. components in the cat). Personally I wouldn't punch them out, I'd get a muffler shop to make one using then ends cut off from the old cat or buy a new one. I can't imagine exhaust would flow as well or sound the same going through hollowed out cat vs. a perfectly smooth pipe. It may even sound better (i.e. although this is a bit subjective) and provide a bit of back pressure that engines needs to produce a complete burn of the air/fuel mixture inside the combustion chamber. I tend to trust a Porsche designed system over 3rd party inventions.

Just my 2cents worth
Bill

Bill

springer3

Well said. Also have some consideration for the rest of us who want clean air. Get more performance and greater weight savings from muffler bypasses.

Geoffrey

I have a Fabspeed cat bypass that was used for 1 session of dyno testing only. PM if interested.

Steven C.

Your car will smell of gas with no cat. Turned my wife completely off my last 964. When I sold the car I gave it to the new owner. It passed smog with out it but probably would not in California.

New turbo is getting a 100 cell sport cat so my wife will go out for drives

Wachuko

No real need for a cat bypass... if you still want to replace it with something, get the 100 cell cat Fabspeed sells...

Besides some weight reduction I did not notice any other difference when I did the change. IMHO money better spent somewhere else or on a DE...

911Jetta

to get back to your original question...
checkout this thread Gutting the Cat / Lessons Learned

altarchsa

Thanks for all the great advice, as ususal, Rennlisters.

The link was especially helpful, and the smell issue was the determining factor to not do this.

964russ

Ive got a straight pipe in place of the cat, no smells with my car!
And clean air, dosnt a cat turn one gas into co2 the big bad co2!

amr89c4

Fwiw, I have a Bursch cat bp on my 1989 964 C4 and I get no gas or obnoxious smells at all. Maybe the Wong chip has some impact.

The exhaust note is a seriously mellow sound with the cup pipe and stock secondary muffler.

Arrowhead

To get back to your original question I see no reason a gutted cat wouldn't free up the exhaust flow and save you money from buying a cat bypass. This is what I would have done if I could find an extra cheap cat. I say extra because I know if it every came time to sell my 964 I would have the original cat. I bought a fabspeed cat delete and found it to be baffled inside somewhat like a straight through muffler. I am guessing this is done for exhaust noise.

tgage

I had an extra cat laying around a few years ago and decided to gut it and see how it worked on the targa. It took me longer to gut and clean it out than it typically takes me to drop the engine! Each of the edges of the cone inside are welded to the inside walls, and just when you think you cleaned it out, you find a second coil right behind it. I expect to get cancer one of these days from all the dust kicked out while cleaning it. So, yes, it was a miserable process.

So... was it worth it? No... Car had that nasty smell that comes from not having a cat. I eventually tossed the "experiment" and replaced it with the 100 Cell Cat. The car tended to burb a bit so I also concluded that it may not have had sufficient back pressure. The 100 Cell works quite well with the Steve Wong chip with no smell.

tom

etom

[QUOTE=Steven C.;7136314]Your car will smell of gas with no cat. Turned my wife completely off my last 964. When I sold the car I gave it to the new owner. It passed smog with out it but probably would not in California.


I have a cat bypass. No gas smell.