Post Cat by-pass Install

[ThePointman]

So I finally installed my cat by-pass. Wow what a difference! It is not the best looking thing but it sure makes the car more fun to listen to, yet it is not that much louder. I had this weird low ideling problem where it would only idle at about 650 - 800rpm when warm, well I unplugged the O2 sensor and bam the idle goes right to 950 and smooth no more weak rough idle. Needless to say the O2 sensor wires are present in the pic but do not connect to anything. I am guessing that when the aftermarket chip was installed the O2 sensor was unplugged and along the way when it was serviced someone noticed it and plugged it back in. Thoughts? Also for the guy that asked how to tell when a pcar has had a respray check the pics out and you will have an answer to your question.

Anyway here is the obligatory pics,






It is a daily driver so go easy on the "man is that engine dirty" comments. I am planning on doing a good engine shampoo when I get my leaky return tubes replaced next week.

Is anyone aware of any negative effect from having basically removed the backpresure caused by the factory cat?

[speedracer]

Looks good, where did you find it? I have been thinking about doing this with my 85 sometime in the future. Any noticable difference other than sound??

[Puka Puncha]

Is this the Bursch pipe?

[ThePointman]

Originally posted by speedracer
Looks good, where did you find it? I have been thinking about doing this with my 85 sometime in the future. Any noticeable difference other than sound??

I bought this used off a fellow Pelican in Oregon. I believe it is a Bursch sold new by our host as seen here for $165.00 with new O2 sensor. The car has noticeably better get up and go in the lower revs now for sure.

[TCB]

I did the cat bypass with a Durst premuffler and added the Durst sport muffler. When I tried to use the old O2 sensor my car wouldn't idle so I bought a generic bosh 2 wire sensor and it made a world of difference. I think they don't like to be disturbed. Nice photo's. I also enjoy the sound. Don't notice the performance difference.

Terry

[ianc]

I had this weird low ideling problem where it would only idle at about 650 - 800rpm when warm, well I unplugged the O2 sensor and bam the idle goes right to 950 and smooth no more weak rough idle.

So that would mean - wait for it - replace the O2 sensor?

ianc

[Tcannon88]

Looks great.....I have a Bursch that I was going to put on this weekend. It looks slightly different, less separation at the manifold end. Did you get new hardware and gaskets, or re-use your existing? Any trouble removing the old one?

[jdowty3]

Pulling the old cat and installing a bypass pipe made the biggest seat-of-the-pants difference so far on my SC.

[75Carrera]

I couldn't agree more... The test pipe is a great "seat of the pants" improvement to your enjoyment of your car. I live in a small mountain town where there's no emmissions testing requirements. I also modified my stock muffler to a "two out" or dual exhaust. Out of concern that it might be a little too much droan on longer trips we cut the muffler, welded in a flange at the muffler to bolt the second pipe to. The idea being to put a restrictor plate in for longer trips. To my delight the sound is amazing and the restrictor plate will probably never be needed.
The rear valance was cut (no biggie) and I modified some cheap chrome tips ($14 ea.) to fit and look great. I can't see where the value is in the "special tips" sold in all the Porsche catalogs for $150 to $250!

[Wil Ferch]

Two items:
1.) I'd watch the "taped" area where you spliced the O2 sensor wires...the electrical tape won't be able to handle the heat.
2.) For bolting....you might have a tough time taking the stainless ( ?) nuts off the stainless (?) bolts...galling potential. Factory 8mm x 40 mm long bolts can be replaced with nearly identical sized 5/16 x 18 stainless bolts, partially threaded, 1.5" long...using silicon-bronze 5/16 nuts. Nice....no anti-seize "goo"...and works well. These pieces use an identical 13mm ( 1/2") wrench that works on the stock 8mm pieces...so the lack of these being "metric" is no concern.

Wil

[ThePointman]

Originally posted by Tcannon88
Looks great.....I have a Bursch that I was going to put on this weekend. It looks slightly different, less separation at the manifold end. Did you get new hardware and gaskets, or re-use your existing? Any trouble removing the old one?

I bought new bolts, washers, nuts etc .. and new gaskets. The old ones were prolly original and fell apart when I got the old cat off. The removal was not that hard it just took a bit of time as I did not have a torch to burn the old bolts off. I used an air die grinder and cut the nuts off then a little WD40 and gave them a smack with a hammer and they all popped right out. Reinstall was a snap

[ThePointman]

Originally posted by Wil Ferch
Two items:
1.) I'd watch the "taped" area where you spliced the O2 sensor wires...the electrical tape won't be able to handle the heat.
2.) For bolting....you might have a tough time taking the stainless ( ?) nuts off the stainless (?) bolts...galling potential. Factory 8mm x 40 mm long bolts can be replaced with nearly identical sized 5/16 x 18 stainless bolts, partially threaded, 1.5" long...using silicon-bronze 5/16 nuts. Nice....no anti-seize "goo"...and works well. These pieces use an identical 13mm ( 1/2") wrench that works on the stock 8mm pieces...so the lack of these being "metric" is no concern.

Wil

Thanks for the reply. The car is going in for an adjustment so that I can continue to run with out the O2 sensor. Once that is completed I will cut the wires off of the sensor completely. So in effect the O2 sensor will only be a bung for the hole in the by-pass pipe The bolts I used are indeed 5/16 stainless with anti seize goo used prior to install. So the use of the stainless nuts is a bad idea?

[Wil Ferch]

Common fastener "best practice" is to never use stainless against stainless...at least change the chemistry...have a martensitc (400 series) nut against an ausenitic ( 300 serires) stainless bolt. Galling is a terrible risk.

Si/Br nuts are the ticket against SS bolting.......available through McMaster-Carr. It's been posted here including part numbers.

- Wil