I was informed by a few local mechanics that I SHOULD NOT keep my Catalytic converters (Dual) on my 89 formula because they will be ruined within a few weeks from the increase in HP and power curve change that the motor now has. I have removed them at this point in time but.....

With the Catalytic converters removed, I am getting a LOUD rattling noise coming from the Flowmaster muffler (80 Series) that I have on the car. It happens at high revs of the motor and it is extremely annoying. I called Flowmaster and they said that it was due to the Catalytic converters being removed and they could not speak to me any further about it because I do not have the CATs on the vehicle. Not much help!!

I want to get rid of this rattle but I do not know what to do. I cannot keep buying new CATs all the time because that will be extremely expense. Has anyone else had this problem and what did you do to fix this problem. Is there a better muffler that will work with the setup I have?

2 CATs into one 3" main pipe to muffler with (2) 2.5" outlets to tail.

Thanks.
FAST89

 

First off, I've never heard of an exhaust place saying removing the cats, as that is totally illegal.
As far as the rattle, I don't see how removing cats would cause a rattle, all they do is convert gasses. Is it a metal type rattle?

 

Shields: Please re-read the topic. Mechanics do not work at muffler shops. I said mechanic as in "fix your car with tools". Muffler shops have muffler specialists that install mufflers.

Yes, it is a metal type rattle. I replaced the flowmaster with another brand new one and the same thing is occuring. I have looked unde the vehicle ecuase I thought it might be the heat shield, but it is tight and fastened. There does not appear to be any other place for metal to rattle. It has to be inside the muffler itself. Hangers for tail pipes as looked to be fine.

CATS restrict air flow and if I am getting increased air flow throught the muffler system with the CATs out of the car, maybe this muffler cannot handle the increase of air flow????

 

I've never heard of muffler not handling air flow. I was going to say the heat shield too, but you already checked that. I have the same problem with my heat shield. Good luck on finding your problem.

 

Yea right. And drag slicks can't handle 1.5 sec. 60' times. :P

Just kiddin'.

When does it do it? Just around idle? If so, more than likely it IS the heat shield. Even though it seems tight, it still has a resonance that all metal has. Kinda like a saw blade can be firmly attached to the handle, but if you wiggle the blade back and forth, it makes that "wowwa wowwa" sound. I know 'cause that's what mine does when it's cooler outside. My heatshield, not my saw.

And if you have old cats, then they may restrict the flow a little. Sounds like those guys are used to the OLD cats that blew out after 30K miles or so.

AJ

 

AJ_92RS: These CATS are brand new because I had a problem passing emissions and this fixed the problem right away. I do not know much about CATS so I have to go with there recommendation on this. I know it is against the law, but this car is only driven on teh weekends and it is not a daily driver. I do not have the $300/400 dollars to drain into CATs all the time either. It only happens on high reve of the motor when the trans is at it shift points. It probably is the heat shield but I do not know what to do to rectify it. It makes my car sound like crap and I have a lot of money into this car and I want it to sound right.....not like a piece of rattling metal!! :-)

FAST89

 

Well, if they're aftermarket cats, put them back on. There's no way your motor is going to hurt them.
Ever wonder how the TT Lingenfelter Vette still uses cats. If any car would blow them it would be that. Forget what those knucklesheads said and put the cats back on you'll be fine.
By the way the Z06 has 2 cats as well.

 

When you removed the cats, what did you do with the air tubes that come down and connect to them? If they are still there, they could be rattleing against your pipe. This happend when I took of my cat. They have little clamps that hold them to the exhaust pipe but where they connect to the cat really seems to hold them the tightest. Just something to check. If they were just cut off instead of removed this could cause it. Also, I dont think you are going to blow out your cats. Like mentioned before, they were probably thinking of the old pellet style cats.

Ben

 

Shields: The mechanics had said that the CATs were "sintering". I guess the CATs deteriorate in one spot and it makes a hole so that the flow cannot continue through the CAT.

I don't know......Its scary because I have to rely on someone elses expertise in this case becuase I know nothing about CATs and this weird issue. :-)

I am sure you can understand my concern...these things are not cheap.

FAST89

 

New cats shouldn't sinter. If the car is out of tune it will happen, such as running rich? Are you throwing any codes. I understand not wanting to keep buy cats. But if you can find out what is causing the cat problem, it will help in the long run.

 

Shields: It funny you ask that...... I was having difficulties with high hydrocarbons and I could not pass emissions until I put new CATs on my vehicle. Once the new CAts were installed, I passed with very low numbers. That is why I was initially worried about the CATs and my motor. The ORIGINAL FACTORY CATs only had 28,000 miles on them. Seemed very low to me. I would prefer to put the CATS back on, but I still am worried about sintering on new CATCO CATS. I am not throwing any codes at this point in time...

FAST89

 

I think what he is saying is that just having a better motor will not cause the cats to sinter. If you motor is running good, and in tune you will be fine. There are some pretty high hp motors out there that arent destroying cats and that seemed to be what your mechanic was saying. I dont think that your newfound hp will cause the problem.

Ben

 

ummmm i had the same problem..... its called an exhaust leak........ tighten up the pipe that is where ur cat used to be and if that's not it then tighted up every other damn bolt on ur exhuast u can find.

 

A rattle won't sound like a leak, that will be a ticking sound. Though if that's what you hear, then that's your problem.

 

Marshall: You had the same "metal rattle noise"? So let me understand, you tightened the exhaust and the rattle went away. I have a dual CAT setup, do you as well?

FAST89

 

2 cats make a pack, three constitutes a crowd. All you have to do is ask the mouse!