Will gutted cat cause poor performance??? Don't laugh..read

[legacycontinues]

I have a 90 legacy wagon with 243K on it and running "good." A while back I gutted the cat because it was clogged and ever since then it sounds like crap. I didn't notice any difference in performance at the time because the o2 was shot and throwing a code. I changed the o2 with a new bosh and the car runs slightly better. (uses less gas)

I was wondering if having that massive open chamber (cat) is some how hindering my performance. It sounds god awefull (like a tin can full of rocks) and part of me wants to say I am loosing HP because of this.

Whats your opinion??

[azn2nr]

imo, clean your cat out better.

if your loosing hp its down low becasue you lost a little bit of backpressure which by all mens shouldnt be a real big loss but if you feel like your loosing power thats where its from. when you gut a cat you need to make sure to clean it out good so that none of the element is left so that it doenst sound like a tin can of rocks.

[legacycontinues]

The cat is 100% hollow. There is nothing in there. It sounds like a can of rocks because it acts as an echo chamber for the manifolds...

[azn2nr]

really??? if it caused an echo id imagine that it woudnt sound like rocks. if you want you could go down to a marine shop and get some exhaust hose and a piece of pipe from autozone or something like that. cut th ecat off and connect the pipe using the exhaust hose and some clamps

[evolutionmovement]

Is the heat shield just loose? If you left a baffle inside it and were loose it could do the same thing. If you can't remove the heat shield easy (sometimes the top part can be hard to get without dropping the exhaust), you can just put some big hose clamps around it to shut it up.

Steve

[legacycontinues]

The heat shield is gone, the cat is empty and it sounds like ass. I removed all heatshield from the manifolds to just past the cat.

Picture what it would sound like if you chopped off the cat and put nothing in it's place and then fired it up...

Now picture that same noise in a big hollow metal chamber....

I don't think most of you realize that the cat on my legacy is like a "Y" pipe. You have the two manifolds feeding into the cat and then one pipe going out.

[evolutionmovement]

I have the same exact exhaust as you. Can full of rocks sounds like rattling to me. All those other posts happened while I was writing mine.

A big open chamber would affect exhaust tuning, reflecting pulses back to the motor, which would change performance a little and maybe exhaust note, but it shouldn't be much louder unless there's a hole somewhere. What about the manifold to head gaskets?

Steve

[legacycontinues]

I checked for leaks....nada.

If there was anything in my cat then it would clog up the outbound pipe when I accelerate but I know for a fact she is bone dry...I even ripped the baffles out. It basically sounds like a lawn mower.

I just need to find an exhaust shop (or someone with exhaust knowlege and tools) that are willing to get er done.

I can't weld for crap! So if anyone knows someone in FL that will do it for a good price...I will drive there! Let me know!

[legacycontinues]

I meet a guy that builds race cars!! He is going to weld me up a custom exhaust!!!! SWEETTTTTTT!!

Zoom zoom bitch!!

[BAC5.2]

No offense to Steve, but a 90 L wagon isn't gonna 'zoom zoom'

When you hollowed out the cat, you effectively created a giant area for exhaust to slow down.

When this happens, flow is reduced, and pulses become more spaced. Where it's rattling, is probably just after the now-hollow cat, and it's bouncing the upper heat shield on the mid-pipe. That's where I would expect flow to be least consistant.

Though, if it sounds like rocks in a tin can (and you don't think it's rattling), you could just be detonating like a motherfucker. I doubt that's the problem, so it's probably just a rattling heat shield.

Hollowing your cats is a stupid idea. It's better to run a pipe through your cat, so you can at least have a constant diameter exhaust.

[evolutionmovement]

Wouldn't the pulses be closer together, creating back pressure as the incoming hit the slower moving pulses much like traffic? The open chamber will also reflect pressure waves back towards the engine which in theory could help pull gases out at higher engine speed (due to the shorter effective length of pipe) except for that whole back pressure thing which would negate any possible benefit.

Steve

[legacycontinues]

There are no heat shields. I hollowed the cat out with a prybar and a BFH!!!

I didn't cut it open and gut it. I cut the pipe in the rear of the cat and dropped the cat with manifolds. Drove that prybar into the cat and hit that sucker untill all the sheeot was out. Took me all night but that sucker is hollow.

It will all be in the past very soon as I am getting a custom exhaust from the engine to the bumper.

What size pipe is used coming off the manifold??

[JasonGrahn]

small. If you're going balls-out with a custom exhaust, might as well have it ceramic coated. Now that'll speed up those exhaust gases!

[legacycontinues]

I am having a place that builds race cars do it. It is going to be real simple. No cat but I am wondering what to use for a muffler.


Any ideas?

[BAC5.2]

Straight Pipe.

Mufflers are overrated, fo sho.