PorKen

I redoing the exhaust on my '81. I'm pretty sure the 3" system I made was just noisy, and not the best flowing.

This time I'm trying to reuse factory parts as much as possible. My '81 isn't ever going to make much more than 200RWHP, if that, so the factory 2.5" single pipe is large enough.

I had a spare cat-back system from an '83, so I cut open the rear muffler to see if it could be modified for more flow. I cut the case with a cutoff wheel on a grinder. I opened both the top and the bottom, but for modifying, only the bottom need be opened. I closed it up with stainless steel MIG wire (the whole exhaust system is heavy gauge SS).

Here's what it looks like inside: (In the pics, I've already started removing the perforated restrictors.)



Pretty simple, really. One or two inlets, capped at the end. Exhaust goes through the perforated holes. Two pipes with bellmouth tips go from the top of the muffler and exit out the side. There are two screens which block off 1/4 of the volume on each end. The muffler's skin is made of two sheets of SS.

The small round welds on the case skin hold the screens in place. Maybe there was once fiberglass behind the screens?

It's not really any louder without the restrictors at idle. I haven't driven it yet.

Tampa 928s

Let me know how you end up I'm real tempted to do this with mine to get a little more noise out of it!

JKelly

That's pretty interesting. Hurry up and drive it!

PorKen

Driving around, it's maybe a tiny bit more 'boomy'. At full throttle there's a nice muted 'wooosh'. I want something that flows well, but quieter, so I don't look like I'm trying. With the cat replaced with a Y-pipe, I think it should be just right.

I went by a muffler shop to price some stainless 2.25" 45s to make the Y-pipe. Ouch! $70 per! I'm sure I could get better prices on the internets, but I am going to go full on recycled SS, instead.

I am going to mod my stock '81 pumpkin, and reuse the '83 system for the Y-pipe. I can use the bell mouth pipes inside for the angles, into the straight 2.5", retaining the stock doughnut flange. The header pipes are from my old '86 cat, which have 2.25" pipes, versus the wimpy 2" on the '81 cat.

Also, I'm going to gasket match the '81 manifold outlets with a little bit of Dremeling. The gasket is 55.5mm, and the manifold opening is 51mm! I may also hook up a variable resistor on the TempII, switched in by the full throttle switch, to adjust the mixture, if need be.

All this is in preparation for this coming Sunday dyno day, out at Louie's.

BTW, it took a bit of experimentation to get the voltage and wire speed right, but I'm welding the stainless just fine with 75/25, no fancy tri-mix.

Tampa 928s

Hey

It seems all you did was remove the baffles looking at it seems like the air bounces around than goes out the pipes is that right? I have an 86 a assume this would look the same and I only need to cut and remove the bottom while on the car. So how much louder?????

Tampa 928s

Has anyone else done this, I'm real tempted to open mine up to increase the sound level.

PorKen

Yes, all I did was open the case, and cut out the center 'holy' section of the inlet pipes. The pipes extend into the other side of the case, but they are welded shut, so the exhaust only goes through the holes 'drilled' in the pipes.

The exhaust still has to make it's way up and out the side pipes, but it should flow a lot more.

I have the car in the air. Tomorrow, I will make a X/Y-pipe to replace the '81 cat and head pipes. If I have time I will test run it with the stock '81 muffler, before I cut it open to remove the restriction. I'll take pictures of the inside of the '81, too.

Tampa 928s

Sounds good, you said you did not find any packing in the muffler is that because of age or there is none. I'm wondering after you removed the centers what keeps the sound from going real loud could it be the bouncing around inside?. With my X-pipe no cats and RMB I got a ticket, I just want to take it up a notch with out adding new mufflers.

Tampa 928s

How did you make out I am waiting to find out I need a project real bad, part of the rehab for my heart!

PorKen

I made the funky X/Y-pipe from various bits from a '86 cat, and the '83 cat back. It took all day, but it turned out well. I took care to keep the insides smooth. I didn't get to start it yet as I need a 02 sensor size tap to clean out the threads, as the old sensor was stuck in there.



The factory resonator is a nice straight through design.

atb

The new H/Y pipe?

Tampa 928s

Not much to that resonator, I had the X-pipe with resonator and RMB only and received a ticket. The X pipe sound was very weird kind of uneven, I put the muffler back on and way too quite. So I'm looking to hear your feedback with the mod muffler and X-pipe in place if its worth it for me to do.

James-man

PorKpipe

JKelly

Porkenpipe

JKelly

When I use my Ott X-pipe with the resonator and muffler (on 86'), the exhaust sound becomes very raspy. If it was possible to mod the resonator and/or muffler to get rid of that annoying rasp, that would be cool.