Gen 3 factory muffler mod

2000TransAm24

Registered
Hello everyone! Just thought I'd share a little mod I did to my gen 3. I wanted to do a dual full exhaust but the options right now don't exist. So I decided to decat the factory mufflers. I wanted to accomplish this without cutting/welding etc. This was a learn by doing and I didn't take pictures of my progress just before and after. I think this will be appealing to those who can't afford exhaust at the moment or the California crowd. This requires some patience, and alot of elbow grease. The curvature of the inlet pipe makes it difficult but not impossible to remove all the material.

Tools needed
Drill
Rubber mallet or hammer
very long straight blade screwdriver 20 inch
long drill extensions
pen magnet
long needle nose pliers 16 inch
crow bar
1 3/8 and 1 1/8 hole saw. These don't need to be exact, in fact If I did it over again I would use no bigger than 1 inch for the cats

I basically started with the long drill extension with 1 1/8 hole saw and drilled shallow holes working around the perimeter of the cats. Then I used the deep 1 3/8 hole saw to drill down the middle. Try to hole saw the cat completely in half. Be very careful because it will catch and spin the muffler right out of your hands. I did this all without securing the muffler to anything but it would help if you did. Once I was satisfied with the number of holes drilled I hammered the screwdriver between the catalytic material and the wall, then pried and twisted to break it loose. I used the needle nose to grab what I could but it is very tricky. Luckily once I did this enough large chunks of catalyst fell into the muffler. Once I got all the big chunks out there were some catalyst still remaining stuck to the wall. This is where the crow bar comes in handy because of its curved end. Just gently insert and feel where the cat begins, be careful there is a lip right before the cat that you don't want to hammer on. Some pieces were big enough to pen magnet out whole and some pieces I had to use the screwdriver like a chisel to break them in half to remove. A couple of pieces were really tight but I was able to grip them with the pliers and pull them out. There were just a few tiny pieces of catalyst left stuck to the wall that I didn't worry about. Once that is done I used the 1 1/8 bit on the outlet side of the muffler to allow some more airflow. You can use the 1 3/8 if you wish but I went smaller to see how loud it will be first. Then I just used the pen magnet inserted all the way down the inlet side of the muffler while shaking it to get all the smaller pieces to stick to the magnet. That process had to be done many times. I haven't put these back on yet to see the difference in sound but so far I'm satisfied with the result. The first muffler took forever and I used a slightly different method. The second muffler went much faster. The picture of the mangled catalyst was my first attempt. I also plan on using compressed air to blow any remaining loose pieces out before reinstalling.

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pcs

Registered
we had talked about this a few months back
i decided against it as i plan on leaving the stock exhaust intact if i ever go back to stock. awesome that you got it done. any sound clips. stock a shop vac in there to pull any remaining pieces.
 

Martin.UK

Registered
I'm not one for doing this sort of exhaust mod myself so i dont know. But do you need to remap the ecu or will it still be ok running a stock map on any of the 3 busa gens if this is done ?
 

pcs

Registered
a bunch of people have swapped to full exh systems and not needed a remap to get their busa to run right. im guessing your set up wouldnt be much different from slip on mufflers. one member here just unbolted the stock mufflers and runs it open header style. didnt say he had any check engine lights or running bad.
 

Oldsoldier47

Donating Member
Registered
I'm not one for doing this sort of exhaust mod myself so i dont know. But do you need to remap the ecu or will it still be ok running a stock map on any of the 3 busa gens if this is done ?
As pcs wrote above plenty of Gen 3 owners seemed to have changed exhausts. I ended up fitting the Akropovič full system (single sided) - works extremely well without remap - saved lots of weight and on the dyno gained a few bhp, a couple of ft lbs and seems to have smoothed out the air/fuel ratio particularly at low revs.

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chidago

Registered
I agree, I have the full yosh system, no hint of a cat..lol and no, meaning zero, fueling issues, cold or hot..no problems with shifters, pegs, etc anywhere..all things lined up exactly, 2 o2 bungs, and decent instructions..BUT, it aint a gen2 redo, like brocks is..with the o2 splitter
 

2000TransAm24

Registered
we had talked about this a few months back
i decided against it as i plan on leaving the stock exhaust intact if i ever go back to stock. awesome that you got it done. any sound clips. stock a shop vac in there to pull any remaining pieces.
Indeed, I read that thread and many others trying to see if anyone had done this. No sound clips yet. Hopefully I'll have it back together this weekend. Unfortunately, I don't have any vacuum attachments that will fit in there. It's just a shame taking videos of exhaust sounds never quite do them justice. I just hope the exhaust note it not too raspy.
 

sixpack577

Top Gun
Donating Member
Registered
Indeed, I read that thread and many others trying to see if anyone had done this. No sound clips yet. Hopefully I'll have it back together this weekend. Unfortunately, I don't have any vacuum attachments that will fit in there. It's just a shame taking videos of exhaust sounds never quite do them justice. I just hope the exhaust note it not too raspy.
I bet it'll sound good, and like most any set of slip-on mufflers.
 

funnyman3000

Registered
... or the California crowd.
I think the California crowd should be the last people to consider drilling out their CAT. I wouldn't be surprised if modifying a catalytic converter is like 20-30 years versus manslaughter is only 10-15 years. They're actually better off saving their stock units to throw back on every other year to pass the required smog check.
 
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