(on stock engine)

did it, dont bother.

one. no power +
two. not much louder. louder and deeper, but not much.
three. crackles in the muffler, sounds kinda crappy
four. good luck not having exhaust leaks when you put it back together.

just take off your muffler, and have duel tips made to exit out the back of the car as if you did have a muffler. leave on the cat. sounds MUCH better.

anyway, just thought i would let anybody know, what the problems could be and lower expectations, because mine were high. Hypothetically it removes a big restriction, in real life, you still have an lo3. so it doesnt matter.

 

my car sounded nice with no cat, i had the borla adjustable cat back at the time too.
i did not notice any seat of the pants gain, but at thte track i picked up a whole mph.

later
tim

 

a gutted cat and a test pipe are different. they sound different and i felt a little difference. i have a gutted cat on my LO3 and i dont like it, too much crackling on the on the way down from high RPMS.

 

i hated my gutted cat, so I replaced it with a 2 1/2 pipe a week later and I love it, there was definitely a difference in sound.

 

Whether or not gutting the cat makes a difference depends on how clogged the cat is. On my cavalier it made a huge difference. A hollow cat won't make a car sound any better, it usually makes them sound a little louder and a lot trashier.

 

yep i once just had a pipe in there now there is that gutted car. straight pipe is defineatly louder as well as meaner sounding. i hate the gutted cat. but thats ok 3" exhaust is on the way

 

another neat trick is to get the cat shell off of a late model jeep, you can fit a 12inch long glass pack inside it. so it flows very freely, isn't too too loud, and if anyone looks they will think there is a cat there
my buddy put one on his 86 t/a. at a glance you woudl never know the difference.

later
tim

 

My old gutted cat made alot of noise. I did notice that the exhaust was louder but not very tuned sounding. I hated it after a while.
I just got a custom exhaust put on my car today and it rocks. The guy cut my edelbrock Y for the TES headers and fitted them for a 3in outlet instead of the 2 1/4 edelbrock sends it out with. He then welded in a race-ready cutout in front of the cat so I could run uncapped. That dumped into a 3in Random Technologies high-flow cat, then 3in cat-back to a Flowmaster, and then out to 4in polished stainless steel tube tips that are about 2ft. long. It sounds SOOOOOOOOO sweet with my new LT1 cam. It has a really low agressive note that it very noticeable . He said that it was important to use the 4in tips as a chamber to echo and tune the sound. What ever it is it works. Before I thought I had all 2 1/2 in pipe before but it was all 2 1/4 back to a flowmaster. Going up to 3in makes your exhaust sound sweet. It is a big difference ...and the cutouts for the track should give me an extra tenth or two. Well worth the money

 

That's pretty much it.

 

help exlain to me why with the cat on, exhaust pipe back to the muffler and no muffler there sounded so good.

I will be removing the cat and replacing it with a pipe soon then i guess. guess i should have did a search before doing it. LOL. ahh anyway... Its still a 305.

69 will be headers. 3ft 3" pipe, and then. em, NOTHING> unless the cam makes the 355 too loud to think.

as for power. is gutting cat equal to adding headers in reducing restriction? should i put my 454 tbi back on and tune a chip with a bit more gas and pump shot?

now that i am in the real world of real mods. (building 355 for 69) there is no way this 305 is staying in stock form any longer.

 

is gutting cat equal to adding headers in reducing restriction? no, while removing the cat removes some restriction (unless it's high flow), gutting the cat may actually increase resistance to air flow. this is because the air goes into a big empty chamber, where it swirls around and impeads flow. you have more restrictions from the cat back. that is why everyone sells cat back systems. here's my understanding why. the factory pipe is the same size so that can be disregaurded. the two things to look at are the number of bends in the exhaust and the increase in heat. the number of bends increases the resistance as the exhaust gases flow around each bend. the more bends, the more resistance and thus back pressure. if you compare before and after your cat, the back is snaked every which way but loose. the second culprit is the cat itself. since it is supposed to burn up unused fuel and gases, it creates heat. hot gases expand. now you have more volume flowing after the cat than you did before.

headers - one of the main reasons for headers is to allow each cylinder to completly expell waste gases. with the stock manifold, multiple ports run past a common point and impead each other from pushing all theer exhaust out at the same time. this leads to less O2 in the cylinder durring the next stroke because of less fill or space available for new air to come in, thus less power. there are also other advantages such as scavenging and heat dispersal that i won't get into now.

if you're going to mod your exhaust, start from the back and work your way forward. yes, adding headers first will show some power, but not as much as if you remove the restrictions down stream.

has anyone noticed poorer gas milage w/ a gutted cat?
a friend of mine and several others have reported poorer milage with a gutted cat. the only reason i can think for this is that the turbulance in the cat is more restrictive. has anyone else experienced this? any other thoughts on the topic??
jess

 

My Cavalier's gas mileage didn't change after gutting it.

 

I replaced mine with a 3" pipe when I did my headers and it sounded awesome.
How it sounds

 

eric, convert that wav to mp3 so it downloads faster.

thats what my exhaust sounded like when i had a cat but no muffler. it sounded so good like that. BUT NOOOO, I HAD TO HAVE 3" CHROME TIPS

 

I have no cat in my system. I have hooker headers, straight 3" pipping to a flowmaster exhaust. It sounds pretty good and is somewhat loud. Soon I will put dual Turbo Apex-i N1 mufflers...now that will be loud...

 

I gutted my cat when I thought it was clogged (wasn't) and noticed no gain in performance but a big difference in sound. The car sounds like it's got ballz but the difference between my setup and most LO3's is that mine does have big ballz . J/k, .
Really though, I'm glad I got rid of the cat. It was too much trouble and just something else that could go wrong. Oh yeah, did I mention that it melted my 2 month old carpet!!! Yeah, got real hot, not fun. You should definatly use a pipe and not just leave the cat gutted. I hope to have time this summer to install a 3" pipe inside the cat. This will give me back the "normal" sound and help performance.

 

think ill melt the carpet with my lo3?

 

I think he meant he melted the carpet when the cat was still working.

 

I Gutted my L03's Cat, and installed a Flowmaster Catback all at the same time. gas mileage is 18 MPG City, 22 Highway. Sounds GREAT. Picked up .3 In the 1/4 Mile. (16.1 - 15.8)

-Off topic-
Added open element, (15.8 - 15.75)
Added Manual Lockup Paper-clip (15.75 - 15.6)
Added Prettier Rims (15.6 - 15.6)
Added ShiftKit (15.6 - 15.57~~)
Added Better Chip and octane (15.57 - 15.3)
Added 12" Subs (15.3 - 15.31~)
Added Better wires/plugs/rotor (15.3 - 15.24~)
Added Manual Fan Switch (15.24 - 15.2)
Added Knowledge "Learning how to drive" (15.2 - 15.19~)
Added New springs and Roller Rockers (15.2 - 15 FLAT)

Best Run to Date:
14.91 @ 89 MPH