cat delete

Emulators are illegal. No idea if anyone else has started making them but the last guys I knew about got raked over the coals by the EPA and they shut down their business. However, there are two other ways to do it. One, have the rear O2s programmed out. Works every time. Two, get a couple of spark plug anti-fouler plugs and install them on the rear O2 sensors. The inside needs to be drilled out, as detailed in this writeup from a Mitsubitchy site. This works, but is not guaranteed.

I would point out though, that cars without cats tend to have an unburned fuel odor about them, and cats in good working order really don't impact power or fuel economy. It's doubtful that you would notice any change unless the cats are clogged or damaged. Removing them will also make the car louder.


Anti-fouler
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How it looks installed.
DSC02881.jpg
 
I have to agree with the old school exhaust smell, I killed my cats and I hate it after a while.
 
Why not just delete your resonaters and or mufflers? You will get a more raspy/deeper sound.
 
its not an issue of sound its with regard to colgging cats and the secondary effects from a failing cat..if its not there you havent back pressures from a clog and less of a chance of much more expensive problems.....
 
If you have failing or clogged cats then I guess I can understand. Cheaper then buying new ones. But not sure that's a good long term fix. These cars probably run better with some slight back-pressure. In addition to the fuel smell, might also get less MPG. Only one sure-fire way to find out though :)
 
Backpressure is bad, and a clogged cat causes it. Cats are sized to take the blockage into account in their design. On a new cat, there's going to be enough area across all the holes in the substrate to equal the inlet and outlet holes of the entire cat. In theory, there should be no backpressure as a result of a cat. I think the reason people have some weird obsession with backpressure is one, turbocharger enthusiasts talk a lot about it because a turbo DOES cause backpressure by its design, and the amount of backpressure must be managed. And two, because an engine with no exhaust at all runs far worse than one with an exhaust system. Add an exhaust, must add backpressure, right? In reality a proper exhaust will scavenge the cylinders which adds power, but an engine with no exhaust at all has no means of scavenging.

Exhaust scavenging for those that don't know is where the exhaust pulse from one cylinder will apply a vacuum to the exhaust system behind it just in time to draw on the next exhaust valve that opens. Exhaust has mass and speed, which is what allows this to happen. You can even feel this by putting your hand over your exhaust pipe. On a properly operating system you should feel a series of puffs at idle, not a constant stream. In fact, a constant stream is a sign that the cat is clogged or the muffler has collapsed. A constant stream instead of the little puffs means the exhaust is backing up somewhere in the system, which is smoothing the pulses out. No idea if this check would apply to a turbocharged engine though, since the turbo is a backpressure-inducing obstruction in the system.
 
failing coils took my cats nine lives, and the only reason i done feel like replacing them is because i dont want new cats to get damaged by more failing coils (i do feel a slight miss creeping back)
 
Telco said:
Backpressure is bad, and a clogged cat causes it. Cats are sized to take the blockage into account in their design. On a new cat, there's going to be enough area across all the holes in the substrate to equal the inlet and outlet holes of the entire cat. In theory, there should be no backpressure as a result of a cat. I think the reason people have some weird obsession with backpressure is one, turbocharger enthusiasts talk a lot about it because a turbo DOES cause backpressure by its design, and the amount of backpressure must be managed. And two, because an engine with no exhaust at all runs far worse than one with an exhaust system. Add an exhaust, must add backpressure, right? In reality a proper exhaust will scavenge the cylinders which adds power, but an engine with no exhaust at all has no means of scavenging.

Exhaust scavenging for those that don't know is where the exhaust pulse from one cylinder will apply a vacuum to the exhaust system behind it just in time to draw on the next exhaust valve that opens. Exhaust has mass and speed, which is what allows this to happen. You can even feel this by putting your hand over your exhaust pipe. On a properly operating system you should feel a series of puffs at idle, not a constant stream. In fact, a constant stream is a sign that the cat is clogged or the muffler has collapsed. A constant stream instead of the little puffs means the exhaust is backing up somewhere in the system, which is smoothing the pulses out. No idea if this check would apply to a turbocharged engine though, since the turbo is a backpressure-inducing obstruction in the system.
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backpressure is good for torque... Typically we wouldn't really care, but the LS's reluctance to downshift (meaning that it's relying on torque for acceleration) means that it's more necessary than it probably should be.
 
Elemino said:
backpressure is good for torque... Typically we wouldn't really care, but the LS's reluctance to downshift (meaning that it's relying on torque for acceleration) means that it's more necessary than it probably should be.
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Back pressure is good for nothing, there is no way that back pressure would increase torque, the scavenging from a set of tuned headers helps torque. There is no use for an engine to have back pressure, it is just a huuuuuge myth that people need to stop spreading around like a high school rumor.
 
+10000000000000000000000000000000000000000000000000000000000


2002_lincolnls said:
back pressure is good for nothing, there is no way that back pressure would increase torque, the scavenging from a set of tuned headers helps torque. There is no use for an engine to have back pressure, it is just a huuuuuge myth that people need to stop spreading around like a high school rumor.
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if back pressure made more torque, then nascars, dragsters, and all other balls out fast as fast gets cars would have restrictive exhaust systems to cause back pressure and increase their torque even more...
 
1LoudLS said:
if back pressure made more torque, then nascars, dragsters, and all other balls out fast as fast gets cars would have restrictive exhaust systems to cause back pressure and increase their torque even more...
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It's good for torque, bad for hp. So no, they wouldn't.
 
Elemino said:
It's good for torque, bad for hp. So no, they wouldn't.
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Strange, since HP is just a number defined by torque:
HP = Torque x RPM ÷ 5252

The misconception is most likely from engines not being properly tuned after exhaust restrictions are removed.
 
Elemino said:
It's good for torque, bad for hp. So no, they wouldn't.
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ok lets try this again, I'll try to keep it simple so you can keep up. the myth of back pressure comes from people's misunderstanding of velocity and scavenging.

OEM exhaust systems usually have the most restriction. good companies will spend the time to make them as efficient as possible and can get them to have pretty low restriction and still quiet down the car (just look at the 2nd gen LS) the important part is to get the right sized piping, because you need to keep the exhaust pulses moving, and the faster the better. with any sized exhaust pulse, the smaller the pipe you have, the faster the exhaust pules will travel. behind each exhaust pulse is a low pressure spot that will help suck out (scavenging) the next exhaust pulse from the next cylinder in the firing order. and the faster the exhaust pulse is the stronger the scavenging will be, now there will be a point where too small of a pipe will be too much to flow the volume of the exhaust pulse, and will start to cut the gains of the faster pulse. also making it tougher to choose the right sized pipe, a smaller pipe will work great for low RPM's but will get overloaded at higher RPM's making small pipes look like they create torque but hurt horsepower. A bigger pipes will flow more volume helping a motor on the high end and helping it make more "horsepower" but the larger pipe slows down the pulses and hurts scavenging which hurts creating power at the low end and is "bad for torque". as a lot of people have a hard time understanding the true complexities of the modern combustion system, they need to make up these myths to fill in what they dont get, hence the myth of pack pressure.

this is also why it is possible for a fast car to actually have a little more power with the correct exhaust system VS. open headers, open headers have absolutely no scavenging going on, instead of having some back pressure to make torque.

this also explains why it felt like your honda back in high school lost all that torque when you through on just random straight through muffler with 3.5" piping all the way back. doesn't matter, sounded cool anyway! back to the point, back pressure had nothing to do with it.
 
1LoudLS said:
ok lets try this again, I'll try to keep it simple so you can keep up. the myth of back pressure comes from people misunderstanding of velocity and scavenging.

OEM exhaust systems usually have the most restriction. good companies will spend the time to make them as efficient as possible and can get them to have pretty low restriction and still quiet down the car (just look at the 2nd gen LS) the important part is to get the right sized piping, because you need to keep the exhaust pulses moving, and the faster the better. with any sized exhaust pulse, the smaller the pipe you have, the faster the exhaust pules will travel. behind each exhaust pulse is a low pressure spot that will help suck out (scavenging) the next exhaust pulse from the next cylinder in the firing order. and the faster the exhaust pulse is the stronger the scavenging will be, now there will be a point where too small of a pipe will be too much to flow the volume of the exhaust pulse, and will start to cut the gains of the faster pulse. also making it tougher to choose the right sized pipe, a smaller pipe will work great for low RPM's but will get overloaded at higher RPM's making small pipes look like they create torque but hurt horsepower. A bigger pipes will flow more volume helping a motor on the high end and helping it make more "horsepower" but the larger pipe slows down the pulses and hurts scavenging which hurts creating power at the low end and is "bad for torque". as a lot of people have a hard time understanding the true complexities of the modern combustion system, they need to make up these myths to fill in what they dont get, hence the myth of pack pressure
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+ infinity

I have no idea why that is hard to understand.

You have a curve where the y axis is the pipe size, where y=0 would be the optimum size, and -y = smaller pipe +y = bigger pipe. and the x axis will have torque and horsepower as horsepower is a derivative of torque

So as you get closer to y=0 you get a higher x value. and the farther you go right or left on the y axis the lower the value of x. So aftermarket companies have to optimize pipe diameter to get the highest x value.

Also you must know that pipe diameter has its own equations as well as the angle at which pipes combine or separate.

So the Diameter that causes the highest flow will use a limit equation.

... a lot goes into this :q:q:q:q, and thus why H pipes are terrible for flow, and only a properly designed x pipe will actually do anything.
 
young bucks and science, there is a reason America is nowhere near the top of the list when compared to the rest of the world!
 
This thread offers some of the best explanation and analysis I've seen in a long time!

KS
 
There was an muffler test done a long time ago, like 20 years ago which actually resulted in a quieter muffler having more power than the same model smaller case muffler. The Dynomax Hemi turbo had a 20 inch body I think and made more power in the test than their smaller 14" body. Actually surprised them also, muffler was made to increase power at a quiet level. I had used them on 1 of my Mark VII's and loved them, no drone, but a little growl. Now they are too large for our cars, that size would not fit.

http://www.pontiacstreetperformance.com/psp/exhaust.html

I have not read link below yet, may be interesting.
http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index1.html
 
Telco said:
Backpressure is bad,
I know this is a little off topic but; your refering to a 4 stroke only, correct?
Because I tried researching this awhile ago and I read that for a 2 stroke engine you need a certain amount of backpressure for it to function properly. It seems to make sense but (as you seem to know a little bit about the topic :p ) I thought I might ask anyways..

Edit: Idk what happen to the quote but....yeah.
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