Question about the cats

[Jspafford]

Well aware of why they get bunched up over it. I was just saying to enlighten the guys who want to remove them so the moderators don't have to get bunched up over the issue. Or maybe they like to. Gives them something to look forward to. I don't know.

Sounds like whether you use the term back pressure or exhaust velocity, it's essentially the same thing. They are intertwined. high velocity, lower pressure, lower velocity (plugs) higher pressure. Which is why guys can check for plugged exhaust using their vacuum gauges, right? So all little Johnny-Yank-His-Cats has to know is he's risking a $25,000 fine so he can screw up his truck and my lungs, right?

I have nothing better to do than receive emails about threads being reported because of this discussion.

I read through and see that no one is talking about taking the cat off, so I am going to leave it open.

The second someone says, "Take it off" it will be locked.

 

[Spitfire1975]

of course. That's your job.

 

[Yellowsplash]

Sounds like whether you use the term back pressure or exhaust velocity, it's essentially the same thing. They are intertwined. high velocity, lower pressure, lower velocity (plugs) higher pressure. Which is why guys can check for plugged exhaust using their vacuum gauges, right? So all little Johnny-Yank-His-Cats has to know is he's risking a $25,000 fine so he can screw up his truck and my lungs, right?

Not quite.... Its more dependent upon the size of the engine (displacement), powercurve the engine will mostly be used in, etc.

If you have a stock 4 cyl engine that is driven primarily in the idle-4K range, a stock ~2" exhaust will be sufficient to provide adequite velocity.

On the other hand...

If you took a high horsepower high revving 4 cyl equipped with aftermarket cams that likes to run in the 5k-8k range the same 2" exhaust would be become restrictive as there is more gas flowing per the same given time.

Its not that the exhaust provided more backpressure on the stock engine...infact, it didnt because there never was enough gas flowing through it to become restrictive. It only offered more "backpressure" when more gas tried to flow through it with the highly modified engine. In other words, the velocity maintained through the pipe was adequite for the engine's needs.

Lets try a game.... Drink from a straw. Easy right. Now try to drink your coke from a garden hose... There's less restriction on the garden hose, right? Why is it soo hard for the coke to flow through then?

 

[Spitfire1975]

so, if my muffler, or cats, are plugged/partially plugged, and I am asking you questions about it, should I be telling you I have a reduced velocity problem or an increased pressure problem? And If I just remove my cats, and replace with a 2" straight pipe, why would that mess up the designed operation of the engine?

 

[Yellowsplash]

You should be telling me that you neglected to take care of your vehicle by allowing unburnt fuel, oil, and antifreeze to enter the cat. They just dont go "bad" by themselves.

The "fix" isnt to remove the cat, but rather to fix the reason to the initial problem.

 

[Robert_1967]

Well, I', starting to wish I hadn't mention any thing about my cat on my little truck.


Robert

 

[Yellowsplash]

For the OP....In a manual transmission truck, when you let off the gas the ecu will cut fuel to the injectors (aka engine braking) when the rpms are over say 1500rpm. When this happens its quite common to hear girgling and popping noises, especially from a vehicle with a glasspack. This is also exacerbated due to you not having a cat.

 

[Spitfire1975]

So in other words...if I keep my freaking truck in good working order then I won't have to worry about removing my cats to increase the performance, and then we won't have to have conversations about removing cats, the watchers won't have to get all bunched up over it and we can all breath a little easier....RIGHT?

So in other words....engineers are smarter than me and have figured something out that is actually in everybody's best interest so I should listen to them and not the guy behind the Schucks counter, right?

Huh. Well...I know I learned something.....

 

[Sasquatch_Ryda]

Removing the cats will not increase performance, so yes the Engineers are just that smart.

 

[Spitfire1975]

Who woulda thought......

 

[kimcrwbr1]

dosen`t the bypass valve on the air pump deactivate to cut off air to the exhaust to keep it from popping at least that`s how I read it for my 2.8l

 

[kimcrwbr1]

If you increase air flow eg cam heads intake you have to increase exhaust it is all relative packpressure is in the design of any system the only thing that cools your valves is fuel too much fuel dont get burnt and ends up in the oil or out the exhaust to little back pressure you risk burning valves plugs rings or lean condition if it is a stock engine it will last longer sticking to the design in alot of cases you can add 5+ mpg just getting a new stock exhaust system and the engine will last longer.