I have an 03 Sunfire with 2.2L eco and was wondering if I can eliminate my catalytic converter? One person I've asked said yes and the other says no due to back pressure. Any suggestions would be appreciated
Ahhh. The old "back pressure" story.
back pressure isn't what you want. You want to keep the velocity through the flow in the exhaust system high. The easiest way to imagine that is to use yourself as an example.
Purse your lips together and blow. Slowly increase and decrease the opening between your lips until you find the spot where you can easily exhale, but you get just a little resistance. If you place your hand about 6" from your mouth you'll be able to feel the most air rushing across your skin when you find the perfect spot. You'll find that sweet spot where the air from your lungs is coming out "just right". That is the point of highest velocity. Your lungs are pushing a little, but they're not straining to get the air out.
Another analogy is blowing through a coffee stir, a drinking straw, a garden hose, and a paper towel roll. If you cut each one of those to the exact same length (we'll use 6" again), and match the opening of your lips to the opening of each, I'm sure you can figure out which is going to be the easiest to exhale into; the paper towel roll. But you'll notice something when you try to blow into the paper towel roll. While it's easy to exhale, you have to exhale quickly and forcefully in order to feel the air moving through the tube, if you can feel any at all. Of course the coffee stir will be the hardest to blow through and your veins in your head will look like they're going to explode before you're able to really move any air through it.
I'll sum these up in a list on what you'd find if you actually tried this and how it relates to exhaust velocity vs. back pressure.
Coffee stir - Very little flow overall. A small kid (weed whacker engine) would have an easier time blowing through this than a full grown man (BBC). The velocity would be relatively low due to the restriction from the minute diameter (back pressure).
Drinking straw - Better flow than the coffee stir. Still a little restrictive for a full grown man (BBC) but better suited for a boy between 8 and 13 yrs old (3.8L V6). The velocity would be better due to the increase in diameter resulting in less restriction. Maybe OK for a small displacement, daily driven 4 cyl, and up to a larger lower revving V8 ( Like a 350 in a tow truck or an everyday work van).
Garden hose - Much better flow than the drinking straw. Very little restriction for a full grown man (BBC) with good velocity (air felt by your hand on the exhaust end). Very low resistance (back pressure). Great for a mid size, high revving V8 (+500HP 350) or a mid revving BBC in the 600 HP range. Would be very hard for a little kid (4 cyl engine) to really move air through the garden hose due to no resistance from the large diameter compared to his little lungs. Velocity would be lost as the air went through the tube.
Paper towel roll - The best flow of all four, but absolutely no velocity. Even a huge man, like Andre the Giant would have trouble being able to feel the air flow on the exhaust end using his hand. Something this size would be good for a stack pipe on locomotive or a cruise ship where the RPM is lower than 1,000, or at a constant rate.
The great thing about building velocity is the negative pressure (or "void") behind each pulse of exhaust from each cylinder. For simplicity, we'll use a 4 cyl engine, and the firing order is 1-2-3-4. As the #1 cyl. is lit, goes through the power stroke, and is then pushed out the exhaust, the velocity built from #1 is just reaching the collector in the header right as the #2 cylinder is starting to exhale. The negative pressure that is left in the collector by the #1 cylinder's exhaust will help draw the exhaust from #2 down the primary tube into the collector. As the pulse from the #2 cylinder leaves, it will help draw the exhaust from #3. etc., etc.
It would be equivalent to attaching a "Y" fitting to the garden hose so it has two "in" tubes and only one "out:" and putting two teenage boys on either "in" tube. The velocity from one small amount of airflow will help "carry" another small amount. That will actually make the engine more efficient at ridding itself of exhaust. Why do we want that? The engine is a big air pump. The easier it is to move air in and out, the less mechanical loss there is.
That's why the diameter of the exhaust is so important to, not only the engine size, but also the intend "normal" operating RPM of the engine. Let's us a SBC 350 for example. If you want more velocity at lower RPM for towing, use smaller diameter primary and exhaust tubes (1-1/2" primaries, 2-1/2" pipes). Higher RPM for road coarse and drag racing, use larger diameter primary and exhaust tubes (1-7/8" primaries, 3 to 3-1/2" pipes).
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i personally dont run one but im also turbo but removing it is up to you since it is illegal and it depends if your state does emission checks best bet would be to just do a quality high flow cat
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Sounds like its coming off since my intentions are to turbo my ride anyway
or u could just gut it out
i run one from performance curve, its a small stainless spun converter. i just feel better having one on there. Dual purpose IMO, cleaner and mufflerish.
