M&K Premuffler and related tuning question
 

I just got my premuffler from Brian and it looks outstanding! I can't wait to put it on and test it out this weekend. I do need to plug the O2 sensor opening as my car is a '79, and this site has kindly answered my question. The necessary plug is a M18x1.5 drain plug from the local auto parts store. Fit like a glove and is the perfect length. Also, I am aware of soaking the bolts in penetrating oil leading up to the installation to remove rust and other crud.

Unanswered question:
Since I don't have the O2 sensor, my car won't know anything has changed. Should I be expecting to adjust the mixture? I haven't been able to find the answer as everyone seems to post about their late model SC.

Finally, here is the work of art:
http://forums.pelicanparts.com/uploa...1485301614.JPG
http://forums.pelicanparts.com/uploa...1485301614.JPG

My car has the same artwork installed!

It's gonna be STINKY!!

Nothing bad will happen by testing emissions and adjusting if necessary...

You may need to adjust the idle mixture on your SC depending on what condition the premuffler or cat was in when removed. The Lambda system should keep the mixture on the lean side but not always as it is aging. Carrera's tend to smell at first more than SC's due to the Motronic EFI adjusted for the catalytic converter.

Thanks Brian. Do you know which way the car will tend towards (lean vs rich) after the swap? I don't have the Lambda system, so it would have to be a manual adjustment.

Freer flow "tends" to lean out a mixture. The right way is to adjust WITH an engine exhaust gas analyzer. Improper mix can burn a piston or just foul plugs.

On a fixed system like you have on the '78/9 SC the AFRs should lean slightly with a new premuffler. That is with all things being in a good state of tune to begin with. The condition of the existing premuffler or cat, and if the engine had been adjusted to compensate for aging, will be the determining factor. Yes a CO meter or AFR meter is optimal to tune.

Thanks guys for the response. That's what I was hoping to hear. The car is tuned pretty well now, so I won't worry about it too much for the time being.

Also, I'd like to pass on my friend's compliments to you Brian. He was extremely impressed by how light it was and how clean the weld joints were. I shouldn't be surprised by it based on all of the reviews, but that doesn't take away from the craftsmanship. Keep up the outstanding work.

Thank you!

Very nicely made premuffler indeed. M&K gets a thumbs up for using an actual perforated expansion chamber to tune the exhaust sound. Fabspeed does this too and it makes a noticeable difference in the exhaust tone- especially if you run an open exhaust on the track like the muffler bypass/delete "elbow" pipe. I've heard the cheapo straight pipes like Bursch and they sound pretty raw.

I'd suggest don't waste your time soaking the nuts for removal. Just cut them off with a rotary disc cutoff tool. Once you've cut the nut or the bolt head fully off, then just use a hammer and a punch to drive out the crusty rusty bolt remnants.

One trick for installing more corrosion resistant bolts is to switch to SAE/English hardware and use 5/16" stainless bolts and silicon-bronze nuts. Works good.

http://forums.pelicanparts.com/porsche-911-technical-forum/118710-s-s-exhaust-studs.html

If you replace the exhaust bolts with new OEM steel stuff it will rust inside the exhaust relatively quickly, based on my personal observation and changing out my exhaust on the former '87 Carrera more times than i'd care to admit

First plan never survives contact with the enemy. As you said Kevin, doesn't seem worth it. I had absolutely zero progress with them. I have a metal cutting bit for my dremel which worked well cutting off pieces of the omega spring. It should do the trick. I'll get back at it tomorrow or Saturday.

You should get his muffler. Just as nicely made and the sound it makes at startup is priceless.

Actually I have been eyeing the 911 sport. But I'm planning to build a 3.2ss, so that will change things completely. Maybe then I'll switch to it. This was a relatively cheap swap for a little bit of fun right now. Besides,the one I've got now sounds great, so there's not as much reason to do such a pricey swap.

After a whole lot of suffering, I finally managed to get the old cat off. While bolting up the premuffler I quickly became very thankful that it fits so well. It probably took about 15 min to install because it took a bit to get some of the nuts to catch on the bolt. The sound is awesome. The idle sounds just a bit louder than it used to (will get a dB reading this weekend for comparison), and it added a nice bass rumble to the exhaust note. Cruising around it sounds about the same, but it roars nicely when you get on the throttle. Overall it was definitely worth all the frustration of trying to remove the old cat.