Cut off cat?

[Chris]

Backpressure?

Seriously guys, educate yourselves on how an exhaust system functions before making yourselves look silly.

Anyway, if the cat is plugged, remove it and replace with an aftermarket unit. Magnaflow spun cats are terrific. Don't be an ass to traffic and the environment by not having one. They don't rob an ounce of power.

 

[Southern Pride]

Wow, I'm sorry. Seems as though I'm throwing around false info regarding this CAT situation...The whole thing with my engine was the valves slowly burned up and it was burning through ALOT of oil like a quart every 150 miles or so, probably more than that. A "MECHANIC" told me that removing the cat converter and running my truck with just piping no muffler, no nothing created no "backpressure" and burnt my engine up...Being a mechanic, I just took his word for it but lately the more I'm learning about "mechanics" and "exhaust technicians" is that they're all full of ****!

Let me take this time to educate myself. It's been my understanding that mufflers just "muffle" the sound but Converters are actually needed for the engine to operate correctly right? Or else GM wouldn't have put them on...If anyone cares to enlighten me as to exactly what they do and explain that it wasn't hurting my engine, please explain so I can learn and not spread LIES!!

 

[carne asada]

i just put a pipe thru my cats then rev it real hard and most of it comes out it ratltles sometimes but its way louder and u can def tell ther is a very good power boost

only thin g is ur light will be on in ur dash, dunno wy but the truck rins great so i guess its a electric problme

 

[Chris]

:rofl2:

Guys, listen. The only way you're going to see 1HP gain from removing catalytic converters is if they're completely and I mean completely clogged. Like your engine is spewing out metal shavings clogged. Any modern converter from ~96-up is high flow and doesn't inhibit exhaust flow any.

It's a common misconception that engines need "backpressure" because oftentimes people will hack their exhaust systems off and replace it with either dual pipes or a y pipe that is too large for the engine. Exhaust systems function by literally "pulling" the exhaust from the combustion chambers. The greater the exhaust velocity, the greater this effect. That's why true dual setups rob so much power, because there's TOO MUCH flow. The velocity of the escaping gases is reduced, and it negatively impacts the engine overall. The same is true for single exhausts with piping too large in diameter. Having a catalytic converter in place will do no harm nor foul from that perspective. (you SHOULD run one however. ever see a picture from a chinese city? that would be us overnight if every hack chopped off his catalyst. they do wonders for air quality)

 

[TLoud]

All a Cat is really doing is taking all of the poisonous gases your engine is creating and turns them into less harmful ones like carbon dioxide, hydrogen, nitrogen and oxygen. I've never heard of the back pressure scenario ruining an engine, most likely if it didnt have enough back pressure it would just run like complete ****... Hence baffles in drag pipes on motorcycles they are only there to create back pressure. When they are removed the carburetor just needs to be re-tuned to get back to the perfect air to fuel ratio. There are many factors in this besides just the Cat for instance your truck could run lean meaning the air to fuel ratio is above gasolines stoichiometric ratio (the perfect air to fuel ratio.... 14.7:1). If it is running rich the air to fuel ratio is below its stoichiometric ratio.

 

[Chris]

:facepalm:

Listen to what you're saying..................BACKPRESSURE. As in positive exhaust pressure in relation to cylinder pressure. An engine cannot run if there isn't NEGATIVE pressure in the exhaust. "Backpressure" is only created when either A) The catalytic converter is completely clogged or B) the exhaust is obstructed.

Your scenario of drag pipes on motorcycles is completely inaccurate. Baffles are used to effectively narrow the ID of the pipe, creating more exhaust velocity. It has nothing to do with creating "backpressure." I'm going to start carrying around a bat and smashing fingers if I keep hearing that word.

 

[Swims350]

I agree with Chris, what burnt up your valves is the air coming back into the pipes, that is why you don't run open headers all the time. My old man swears by it, says the cold air can get sucked back up and it burns the valves. Not due to cat being gone, vehicles didn't get cats til 76 or so, they never burnt valves up all the time because of it. it's not gonna burn valves with no cat or gutted cats.

The whole huge pipe deal is true too, no need, it's easier to push air out with some velocity and scavneing then it is one huge open pipe where it can just stay and swirl around and barely get out.

Think of it this way, race cars run headers right? why? and have long collectors and such. It's for scavenging the exhaust gases out, and not just letting them dump out the head, if you ran something for a good while right out the head it'd burn the valves quicker.

As for retuneing the carb after removing the exhaust, you know why that is??? an engine is an air pump, if you move air out, you gotta move air in. That's why you don't stuff on free flowing heads, intakes and carbs and leave restrictive manifolds on it. Or why you don't run 3 inch duals on a stock motor and 2 inch primary headers on a stock motor. it makes no sense and is not needed.

If you put air in you gotta get it out, and if you get it out, like free flowing or straight headers you sometimes(on atv's and motorcycles) have to rejet to make it work, mostly because of the airflow required and fuel supply etc.

A cat removed aint gonna cause a truck to run lean, it only heats up and burns off the nox and other emissions crap, the o2 sensors are what causes the motor to go lean or rich.

 

[Southern Pride]

Okay...Still heavily confused because seems some still don't know also, but whatevs. I'm running TRUE duals. 2 and 1 quarter pipes all the way back with an after market cat on each pipe, no mufflers (passed inspection with a near 0% hydrocarbon or whatev).. Then 3.5" tips out the back. Is that exhaust bad or "letting air back in"? Should I be worried? I noticed I gained some top end pep with this exhaust, and it sounds amazing.

 

[Swims350]

I have no actual proof on the air getting in and burning valves but it does make sense to me and I was always preached at about it.

The rest I am sure on. It's what I've read and understand on it.

For you, you should be fine, you got alot of pipe to travel thru plus you have cats. I think the biggest and worst worry would be straight headers, or like dumped at the y-pipe.

You have smaller pipes and all that and it works well to push the gasses out, that pop could very well be the air, but most likely I guess the crackling like glasspacks do. I wonder if that's why glasspacks pop and crackle is the air going in them?

I noticed last time I had mine going with just my shorties headers no exhaust it popped alot. Mostly after a rev and it starting to drop rpm's back off.

 

[Chris]

Okay...Still heavily confused because seems some still don't know also, but whatevs. I'm running TRUE duals. 2 and 1 quarter pipes all the way back with an after market cat on each pipe, no mufflers (passed inspection with a near 0% hydrocarbon or whatev).. Then 3.5" tips out the back. Is that exhaust bad or "letting air back in"? Should I be worried? I noticed I gained some top end pep with this exhaust, and it sounds amazing.

Yes, it's terrible. Even 2.250" ID pipe is too large when you're talking about a dual exhaust. There's also the fact the cylinder banks aren't balanced, so that's adding to the misery of the engine. You may want to have someone else drive the truck, and you might change your tune as to how it sounds. The last truck we swapped a 6L into had a similar setup and it sounded "okay" in the cab. Outside however it sounded like a cro-magnon human beating the tarnation out of a steel trash cash with a stone implement.