Cat bypass DIY Question
 

I am looking to install my bypass tonight and wondered what would be required?

The biggest question is do I have to remove the muffler or can I just take the old pipe out and slide the new one in?

Any other tips would be helpful!

It's been a few years since I did it but from what I remember you do not need to remove the muffler. Once you undo the bolts though, the muffler is just hanging there by the two straps, so if you did need to move it, it would be pretty easy.

Other things I would recommend:

-Soak all of the bolts in PB blaster days before you are going to remove.
-You will probably want some MAP gas to heat the bolts cherry red to remove them if they have been on there a while.
-You will most likely destroy some or all of the bolts when removing them, so plan on having new ones to replace. I like to use SS bolts with silicone bronze nuts on exhaust. The silicone bronze nuts will not fuse to the SS bolts.
-Swivel sockets and a long breaker bar are helpful for getting to all of the bolts, especially the ones close to the engine.

That's all I can think of. Exhaust parts can be difficult to work on due to years of heat cycles, so be patient and try to avoid busting knuckles! Good luck.

Have new hardware, preferably stainless, on hand. Unless your car was in a museum you most likely will have corrosion on the bolts/nuts. A dremel tool with a cutoff wheel comes in handy as well.

You probably can swap it out without removing the muffler but I would suggest you at least loosen the muffler straps so that you have a little wiggle room.

Have you been soaking the exhaust bolts/ nuts in penetrating oil for a couple of days?

I would not assume a perfect fit. Loosen the muffler to reduce binding, get the pipe installed and then tighten the muffler straps. Use never seize on bolts. Careful not to contaminate the O2 sensor, I put it in a bag and tape up out of the way. Consider putting some heat wrap near where the pipe is next to the tire and shock.

Yes, a dremel tool with flexible shaft attachment and HD cutoff wheels was very valuable as I remember. I had to dremel off many of the bolts, and a dremel tool will not fit into all of the spaces without that flexible shaft attachment.

My engine was just rebuilt 4,000 miles ago so while the bolts were re-used they should be ok to remove.

I will probably replace them though, does anyone know offhand what size bolts should be used?

Good to know about loosening the muffler

I did this not long ago..I did not need to remove muffler and the M&K pre-muffler fit perfectly.

you should get new exhaust gaskets, 3 required (PP sells them). the old ones may crumble to dust when you remove them. they are about $4-5 each. you don't need to remove the muffler. you will need to swap the 02 sensor also if you have one.

Go to your local hardware store and get a $10 propane torch. Heat the nuts up before removing them.

PET for my 86 listed the bolts as M8 x 40 or M8 x 37. I ordered bolts and copper locking nuts through Pelican. This is for factory Cat. I just ordered all M8 x 40 as the extra 3 mm should not be a problem. I've seen it suggested that you might need to double up gaskets between the crossover/heat exchanger and the Cat bypass if the fit is not perfect.

J

I am doing the same project on my 3.2.

PP sells a "M&K gasket and hardware kit" that contains all 3 gaskets and all hardware for the job. I reccomend this kit to make it easy to get the right hardware from 1 source along with the appropriate gaskets.

You do not have to remove the muffler. You don't even need to loosen it. Forget the PB Blaster and just cut the hardware off with a Dremel. It will be rusted.

Be sure to have the new gaskets handy. You will need them. Go to your local Hardware store and get some stainless nuts and bolts. I think you need eight of each if I remember correctly.

You should be able to get this done in no time. Cutting off the old nuts and bolts will take the most time.

But when you are done, you will have a little more sound out the back, and in my case, a little better throttle response.

And most importantly, have fun. :)

Sounds good and thank you for the advice!

I bought a bypass and gaskets when I had my 85 cab a few years ago but never used them so I just have to find the gaskets, buy bolts/nuts, and then I will be good to go!

Lacking the cutter or gas, go to your local muffler shop and have them R&R all nuts and bolts, replacing with the stainless set you give them. Drive home, let cool, R&R with new nuts and bolts. Worked great for me - gave the guys $ and a six-pack.

Bolts are M8 x 40, will need 9 I think for the cat by-pass R&R.
As noted in a previous post if using stainless bolts and nuts you must apply anti-seize or the nuts & bolts will seize due to galling when tightened. First time I reassembled my exhaust I went the SS route as I planned to have it apart again, sure enough when I went to disassemble it two months later half the SS nuts & bolts were seized. After that I read up on SS fasteners only to find that you can mix materials without issue but if using stainless on stainless they will gall if no antisieze is used.
If the fasteners have been there a long time as mine were, a dremel with the flex shaft is a life saver.

Benefit of removing the CAT on a 3.2?

What are the dyno results of running no cat on a 3.2 (excluding any other mod's, just remove the cat and add a bypass pipe) ?

Or simply remove Cat, knock the stuffing out of it, reinstall. Looks bone stock and improves the exhaust note. Small power increase, heard between 5 and 10 Hp.
When knocking out the internals wear gloves and a dust mask wouldn't hurt. Took a couple hours to get everything out, the material is a tougher than it looks.

So, I got my OBX bypass in and it looks great!

Will install it soon

I would suggest you at least loosen the muffler straps so that you have a little wiggle room.
http://www.lovelv.info/d.jpghttp://www.lovelv.info/h.jpg

De-gutting the cat? hmmm wonder what that would do on the dyno.

Maybe the guts would buy a couple of six packs of Becks, the stainless hardware.....

What is your point? If you have one, make it.

Also, ask direct vs rhetorical questions.

De-gutting the cat? wonder what that would do on the dyno.

My apologies, kuehl. Read it the wrong way as in "What's the point of doing that?"

Bob,

No problem. I'd like to convert the apology into a Mulligan and use it on the back nine if I can.

The original questions are good food for thought though, you gotta wonder how many have actually done a dyno before and after (just testing the by-pass pipe) and how much do the results vary, and if you gutted your cat would you gain anything worthwhile?

Stay well,

Griff

You may want to reconsider if planning to destroy a very valuable cat. If sold to someone in CA you will need it to work.

I'm in exact same boat, had local Porsche shop install OBX bypass today.

Was great quality for the $100 I paid, and fit without any problems.

After an hour with it, my butt dyno says a bit nicer (throatier) sound at certain revs under load and smoother power application.... Then again I didn't have an O2 sensor plugged in before (part of the reason for the switch, long story) so that may have affected things.

More power? Maybe slightly, nothing to write home about though.

Overall: satisfied and worth the minimal money. Will be upgrading to SSI's and a sport muffler in a year or 2 anyway.

LoOking forward to hearing your initial impressions!!

Here is a link that has some quotes from "The Bruce" regarding hp increase. Post #8.

http://forums.pelicanparts.com/porsche-911-technical-forum/56179-bypass-pipe-hp-increase.html

Nothing too exciting, unfortunately.

+1..

I did this the other day, but in reverse. For compliance reasons I had to make the car quieter.

With the bypass the car was over 105db, with the cat (pre-muffler) the car was 90db. Measured by my compliance officers fancy meter.

All the bolts were ok, so no heating required. Before spending money on dremmels, torches and exhaust shops, have a go yourself. You never know. Not the end of the world if a bolt breaks.

I had to do a bit of pushing and shoving to make it all line up, but in the end it was relatively straight forward.

Also note that your car might start smoking a little more after the bypass. http://forums.pelicanparts.com/porsche-911-technical-forum/563905-my-dad-just-installed-cat-bypass-now-we-see-blue-smoke.html

I will soon be swapping it back.

Just an FYI.
Ed

So I'm curious how an officer would go about measuring this?

Surely it wouldn't be at idle and I know they don't have the authority to make you rev your car.

Always been curious so if you could shed some light on the matter I'd appreciate it.

Australian Complaince Design Rules or something like that.

Not the HWP.

I exported the car from UK to Australia. It has to pass noise tests. You are required to rev that car to 4500rpm and a reading is taken. With the bypass on it failed miserably. With the cat in place it was fine.

Cost me 250 bucks to buy the cat, which will now be taken off and sit in my shed for the next 20 years.
Ed

I have a gutted cat I removed from my 87...with a m&k 1 in 2 out it was obnoxiously loud, and metallic...acted like an echo chamber. I have to wonder how well it would flow (small diameter to large then small again), and would the loss of back pressure effect performance. Cat by pass makes more sense to me

Makes sense.

Well, I bought bolts and ordered gaskets.

Also my Dansk sport 1in/1out stainless steel muffler will be here Friday!!!

:cool:SmileWavy