How much restriction does the cat actually Have?

[MoparBob]

Hello one and all. I have a Silent Might muffler sitting at the house waiting for me to come home and install it. My question is this... does anyone actually know how much restriction the cat actually has? Is there any data on this out there? I am as of yet undecided, but leaning towards leaving the cat in for now. Any thoughts and opinions on this?

 

[jelag]

There are several types of designs... . one is a chamber full of pellets... . or round balls... the gases pass around the balls... . think of a jar full of marbles and the gases flowing around them... . each with a porous substance that can alter the chemical makeup of the exhaust ... . the other option that is used is honey comb design... you can actually see from side to the other..... in either design the flow is very good... . the problems occur when there is something that will cause the design to fail... . particles stuck to the side of the honey comb... or heat that will cause part of the system to fail and plug it up... .



So in a new product the back pressure is not bad... its after heat, or chemical coatings that cause most of the problems and that is either non functioning of the cat or plugged exhaust system... .



Hope this helps...



BTW - on older gas engines I've seen many of these fail from excessive heat in the exhaust stream from the customer turning up the HP..... they cause either design to break down and broken down parts going down stream will plug the rest of the cat up...

 

[JVolpe]

Well ours or mine is the honeycomb design. The full large section of the cat is filled with the honeycomb. It has very small openings in the honeycomb. While mine was off for, ugh, cleaning I took this picture. It is looking directly through the cat into bright sunlight. No sunlight visible at any angle. Now the air flow might be very good because of the honeycomb design, but I can see how it is possible for this to become restrictive if collecting particles that are not burnt off.



#ad

 

[2broke2smoke]

if it restricts light ... it restricts flow



great photo by the way, really helps illustrate the discussion

 

[BSwope]

Man those holes look small.

 

[abrankod]

Although the holes were very small... . They had to count them all...

 

[RSByrd]

Ahh, A Day in the Life

 

[jelag]

I might add..... this is like the cat on a car... . or a catalytic heater..... when it gets hot from exhaust gases it will light off... . at a much lower temperature than inside the combustion chamber... . remember there is no flame... ... just a big red glow, like you see on a catalytic heater... . that's why these things are double walled... . if there is too much raw fuel running down the system it will get very hot... and if you remember would light the field on fire when the farmer ran his pickup into the field over the grain crop... in the early years the local muffler shop would build heat shields or put test pipes on the farm pickups too keep the field fires down...



We're going to see the same thing with the guys on this board that over fuel their trucks... remember those that put out smoke... that's nothing more than unburned fuel... when the honey comb design gets overheated it breaks down and starts to flake off and plugs the system...



I had an uncle with a large gas motor home and he'd go down the road and cook the cat and plug the system... Ford must have replaced that cat 4 or 5 times in 2 years... than we installed a special one... that had been apart and was much lighter than the old one..... he never had that problem again... We never figured out why Ford couldn't fix the over fueling problem..... or that engine just used lots of fuel all the time and more than the cat was designed to handle... .



Jim

 

[MoparBob]

JVolpe,

Thanks for the pic... certainly looks restrictive to me. I received an email yesterday that informed me that unless you are pushing 400+ horsepower, you probably won't see any gains (keeping in mind that the cat must be operating properly). It also informed me that the cat in conjuction with the Silent Might (current version) would be about 2db quieter. My truck is still very low mileage so I think I'll keep the cat for now as I can always order a test pipe and delete it later... that is unless someone has actually run dyno runs with and without the cat in place to see if there is a measurable difference. Anyone heard anything on that?

 

[Dieselnut59]

My "cat" on my '96 is very low milage. It has less than 500 miles on it! The truck has 205,000 on it. The cat is in safe storage in the barn. My '03 came without a cat. I have noticed the newer trucks will burn your eyes if the exhaust hits you just right (furd powerchokes are the WORST!)

A trick I have heard is you must at least occasionally "blow the soot" out of the cat to keep it from clogging by doing some high RPM driving for a bit. I used to do this on my mother's 1987 Mercedes 300SDL. Her car's cat would become restrictive regularly. I finally installed the special light weight model mentioned above, minus the honeycomb. Made a LOT of difference in power and turbo spool up.

 

[JNeves]

For what it's worth, I also installed the Silent Might and chose a cat delete from MBRP. Yes it's definately louder especially until some soot collects into the muffler. I then had Imler diesel install a BD VB and TC afterwards we dyno'd the truck. He had just finished dynoing an 05 with a lot more mods than mine and my truck came in with much higher torque and a little more horsepower. Both trucks were at's the other guy had a Banks IC new turbo and Bully Dog with a cat and an Airaid. I have an AFE stock IC and turbo no cat and BD X power tuner running a 90HP download. Basically without a cat that's what made my truck get better numbers.