Cat bypass DIY Question

[Onefastman]

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!

[SpeedracerIndy]

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.

[Oh Haha]

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?

[hcoles]

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.

[SpeedracerIndy]

Originally Posted by Oh Haha

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.
...

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.

[Onefastman]

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

[Dublinoh]

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

[schumicat]

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.

[McLovin]

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

[JAR0023]

Originally Posted by Onefastman

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

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

[porsche0nut]

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.

[CCM911]

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.

[Onefastman]

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!

[Jdub]

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.

[shrtshck]

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.

[kuehl]

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) ?

[shrtshck]

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.

[Onefastman]

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

Will install it soon

[StiltnerCor]

I would suggest you at least loosen the muffler straps so that you have a little wiggle room.

[kuehl]

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.....