DIY Cat Bypass

[ChemMan]

Here is a before and after that Oh Haha was talking about. Before: stock muffler and cat. After hollowed cat and Bursch muffler.

YouTube - ‪Stock muffler with cat. converter‬‏



YouTube - ‪New Bursch muffler plus ride height‬‏

[ChemMan]

One more:

YouTube - ‪1986 Porsche 911 Carrera with Bursch Muffler‬‏

[kdog_us]

Originally Posted by kinein

i am selling it 75 for it i also have a vertex chip also you can have them both for $100, i am supercharging my car so i dont need......

Thank you. I will think it over. Havnt decided what path to go down yet.

[kinein]

yeah no problem its still on the car sitting in the shop being put together soooooo

[Peter Bull]

Originally Posted by kdog_us

Anyone ever do their own cat bypass utilizing most of the existing plumbing? 86 3.2L

As a little experiment to learn to weld with a TIG I made my own test tube form a small pile of stainless tubes and a couple of stainless plates.

A little bit of machining, welding, beating and swearing later, this was the result:



Please excuse the ugly weld beads, but it was my first attempt at welding stainless steel. Anyways, this was how it looked mounted on the car:



/Peter

[kdog_us]

That looks great Peter. I hadnt thought about making my own mounting plates. Good idea. Did you weld in a bung for the O2 sensor?

[Peter Bull]

Thanks,

the car didn't have a cat or an O2 sensor. But it shouldn't be too difficult to fit a bung for the sensor if needed.

/Peter

[DRACO A5OG]

Holy Shiznet! That is Ugly Awesome! How does she sound and feel?

Any change on low end torque and high end torque?

Honestly, not bad for DIY. I am practing on my new welder from HB as well. Any hints or tips?

[MotoSook]

Originally Posted by kdog_us

If its just a matter of coring the cat, why do so many people by the m&k bypass?

Because it's sparkly! LOL!

Really, a gutted cat works just fine. Don't let the internet-dyno cost you money.

I even cut and welded up a Cherry Bomb glass pack for my old 3.0 for less than $30...worked great sounded great without pissing off the neighbors and sounding like a teenager in a Honda with a fart can.

[lupin..the..3rd]

Originally Posted by Oh Haha

Wear a dust mask.

And miss out on the free buzz? Grind that stuff up and snort it!

[djbrand1]

If your going to purchase a bypass pipe, you can sell your existing cat on the forums, or sell to a scrape yard for 50 dollars. Someone mentioned already, there are precious metals that make up the "honeycomb". This is the reason why so many SUV's lately are having their factory cats stolen.

[mkc1962]

I took a standard gutted cat. Got a piece of exh pipe the same diameter as the inside bore of the cat. Drilled many holes in its entire length to identically mimic what the inside of a sport cat or glass pac lining might look like. Then weldeded that section of drilled pipe inside of the gutted cat. Sounded better and throttle response felt better better. How much, dunno didnt test it, didnt care to, just wanted to free up the exhaust a bit. Looked just like it was all still there. It appeared to me that due to the reduced back pressure my older engine was using more oil than it was prior, hence I took it off and put the cat back on.

Sorry cant provide pictures as thieves recently stole the home pc's and camera's.

If interested I might consider selling.

[kdog_us]

how much are looking to get for it?

[Peter Bull]

Originally Posted by DRACO A5OG

Holy Shiznet! That is Ugly Awesome! How does she sound and feel?

Any change on low end torque and high end torque?

Honestly, not bad for DIY. I am practing on my new welder from HB as well. Any hints or tips?

Gee, thanks Even though it looks bad its withstood about 10 years and 100,000 km of abuse.

To be honest, I can't say i noticed much of a difference when i mounted the bypass. No difference in power or torque. Since the car had a cracked pre-silencer and no cat there shouldn't be much difference. It sounds a little bit more, but not much, and there is a slight ting to the sound which I've been told comes from using stainless steel.

I could give you a couple of good reading tips on welding, but I am afraid the books are in Swedish...

/Peter

[DRACO A5OG]

Ja, I know very little Swedish. One of my clients is swedish and she taught me some but not enough for a Swedish tech manual :-P

Still, very good work

Originally Posted by Peter Bull

Gee, thanks Even though it looks bad its withstood about 10 years and 100,000 km of abuse.

To be honest, I can't say i noticed much of a difference when i mounted the bypass. No difference in power or torque. Since the car had a cracked pre-silencer and no cat there shouldn't be much difference. It sounds a little bit more, but not much, and there is a slight ting to the sound which I've been told comes from using stainless steel.

I could give you a couple of good reading tips on welding, but I am afraid the books are in Swedish...

/Peter

[kdog_us]

**Update**
Decided to build my own cat bypass. Here is how it went...

-2 into 1 pipe from the heat exchangers - freebie from the local Porsche mechanic.
-3 hole flange, 2.5 in dia exhaust pipe, flared on one end, and O2 sensor bung - $25
-mounting hardware - $5
-local muffler shop to torch off old hardware - $20

Total cost - $50

Welded together the pipes and new flange, drilled hole and welded in new O2 sensor bung. Final assembly was a piece of cake. Sorry no pics.

Results
Slightly improved exhaust note. Its a little deeper
No noticable power improvement.

All and all, it was a days work, fun and simple.

[Oh Haha]

Originally Posted by kdog_us

**Update**
Decided to build my own cat bypass. Here is how it went...

-2 into 1 pipe from the heat exchangers - freebie from the local Porsche mechanic.
-3 hole flange, 2.5 in dia exhaust pipe, flared on one end, and O2 sensor bung - $25
-mounting hardware - $5
-local muffler shop to torch off old hardware - $20

Total cost - $50

Welded together the pipes and new flange, drilled hole and welded in new O2 sensor bung. Final assembly was a piece of cake. Sorry no pics.

Results
Slightly improved exhaust note. Its a little deeper
No noticable power improvement.

All and all, it was a days work, fun and simple.

Cool!! It's always gratifying when you DIY a project.

What muffler did you use?

[kdog_us]

Stock muffler for now. My budget requires baby steps

[DRACO A5OG]

Try it at speed on the highway or freeway, you will love it when you down shift to 4th