Can someone explain the thinking behind removing the oxygen sensor? In most FI cars isn't the oxygen sensor an inherent component to adjusting the fuel mixture? What happens to drivability/economy/power with its removal?

Also, is it correct that the least expensive SSI compatible two in muffler would be a Dansk @ approx $465? http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=911-111-025-01-M350&catalog_description=OE%20Muffler%2C%20911%20% 281974%29%20

That one says its for a 1974 911 - does it work with SCs since the SSI's backdate the exhaust, or is something like this M&K required?

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=MK-MNEB-21-T&catalog_description=M%26K%20Exhaust%20Stainless% 20Steel%20Muffler%20-%202%20in%201%20out%20-%20Tips%20Polished%2C%20911%20%281974-89%29%20

This would be the least expensive muffler for the SSI's at $169....
Pelican Parts - Product Information: PEL-903080

I used one for a while on my SC, (about 1500 miles). Higher pitch and louder compared to the standard primered grey Dansk one I bought used, and have on my car now.
Dansk Sport is a little louder than mine as well.

Pelican Parts - Product Information: 10-1010-149-M350

The SSI's used to come with the bung welded on it for the FI cars that need it. I guess they don't do that at the factory any more. If you need it, get it welded on.

So the mufflers said to be for 1974 (your second link) do work on an SC with SSIs?

Yes.

SSI's are a 100% copy of the heat exchangers used on '74 911's. The only difference being that they are made of stainless steel. So anything you need to source, you source from a 1974. Don't forget that you will also need to buy the oil lines when converting to SSI's. I really wish there would be a total package available. Gaskets, hardware, and oil lines at the least.

When I got my SSIs for my '78 SC (doesn't need O2 sensor, so didn't need the bunged headers), I ran it with a '74 stock muffler, and I backdated the heat (which you don't need to do, but it's a great upgrade in looks, lightness and works very very well with SSIs). The power upgrade was amazing, and the sound improvement was very nice.

The problem I needed to fix, here in Colorado, was emissions. So I did a custom dual cat, MagnaFlow system. Here's the thread with tons of pictures.

The power improved again, and the sound...well the sound is glorious now! ;)

http://forums.pelicanparts.com/uploa...1358184296.jpg
http://forums.pelicanparts.com/uploa...1358184308.jpg

anyone notice that they are now NLA on pelican? sold to an outfit back east and the price went up.

If you mean SSIs, they were sold to Dansk, if my understanding of the ads in Excellence are correct.

Lufteknic. is that dansk?

Here's what I've put together, not that it's rocket science.

jpgroup is Dansk (www.jpgroup.dk). See the ad on Excellence p. 82 this month.

See the SSI ad on page 86. SSI by JP Group North America LLC, with the same street address in Long Beach, phone number, e-mail address (robert.d@ssibyjpgroup.com) and web address (www.jpgroup.dk)

What do you think?

They used to come with an O2 sensor bung but I don't think they do anymore. You can weld one in. My SSIs came with one but I bought them 12 years ago.

Lambda CIS (80-83 SC USA models) can run with the O2 sensor disconnected. Disconnecting the O2 sensor is often done on this car to improve idle stability due to vacuum leaks, but it will reduce performance at WOT and IIRC also at 0-30% throttle. It may reduce mileage but this can be compensated for by adjusting mixture. The best way to deal with idle problems is fix all your vacuum leaks and leave the O2 sensor system in place.

I used to leave mine disconnected, then after researching how the system works I elected to reconnect it. Porsche made alot of modification to the standard Bosch K-Lambda system to improve performance, so there are some intricacies of the system that are Porsche specific such as the addition of a throttle position sensor which is part of this system, but not on other makes of the period using this same setup.

That explains why my O2 sensor was found disconnected. I am a new owner of an 83 SC. I removed the engine and found the O2 sensor disconnected. I will try to put it back in service and try to remove all vacuum leaks.

I agree, but the PO probably changed the mixture adjustment to compensate for no O2 sensor, so you'll need to recalibrate once you reconnect it. You can get an analog dwell meter and try to set it via this route but I have found this cumbersome. The best way is with a CO meter measuring at the tailpipe, which is something that most home mechanics don't have as it's a little spendy.

Also note that on K-Lambda CIS the O2 sensor does not function until the car reaches normal operating temp, so if you plug it in to try it you won't notice any difference until it's warmed up. The thermo-time switch (on one of the cam covers, can't remember if it's left or right) tells the O2 sensor brain when to switch on once normal temp is reached.

Keep in mind even a properly tuned K-Lambda CIS setup will show some minor idle fluctuation, even with no vacuum leaks. Try to remember to look at it with a 1970's/80's-technology mindset/expectations.

Probably best to tackle this after you get your exhaust update done, then you only need to do it once.