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Exhaust Back Pressure
flat_iv - September 29th, 2010 at 12:20 AM

Anyone ever have any issues with a catalytic converter or sizing a cat for a 2.2 suby engine. I originally had just a muffler that I was using and I wanted the exhaust not to be so loud. I installed a cat and now the engine seems to fall on its face when above 2000 rpms. I believe I have to much backpressure and the exhaust cant excape fast enough. Any thoughts?

rose - September 29th, 2010 at 08:03 AM

take the cat off and make sure you can see day light through it when you hold it up to the sun

flat_iv - September 29th, 2010 at 08:44 AM

I remember doing that when I purchased it. I could see light thru it.

pete wood - September 29th, 2010 at 02:15 PM

THat's kind of weird. Is the exhaust meter still plugged in?

BTW, if you don't need to run a cat for registration just take it off again. They only do their job after 15-20min of proper running. Even then, werl, the gains are debatable.

bajachris88 - September 29th, 2010 at 02:34 PM

emissions wise their gains must be noticeable... otherwise we will have every dual oxygen sensor later efi setup on the road coming up with a cat convertor warning light telling us otherwise...

pete wood - September 29th, 2010 at 07:21 PM

I think the gains that cats make is reducing as EFI systems/oil/fuel improve and other contaminants within modern engines reduce. Also, as I said, Cats have real down sides...

http://en.wikipedia.org/wiki/Catalytic_converter 

Quote:
Warm-up period

Most of the pollution put out by a car occurs during the first five minutes before the catalytic converter has warmed up sufficiently. .[12]
[edit] Environmental impact


To my mind this is the most damning one. In a quick flick round the web I couldn't find any supporting evidence, but as I mentioned before, I've been led to believe that most cats only start to work after 15-20mins of real operation with the engine running for the whole period. For many people, this is longer than their trip to work/school/shops/bowls etc. So what the cat really adds is extra restriction (more performance, then fuel needed for any given vehicle) and more weight (more fuel needed to move any given vehicle). And believe me, they would be the heavier single component in any modern exhaust system by far.


Quote:

Catalytic converters have proven to be reliable and effective in reducing noxious tailpipe emissions. However, they may have some adverse environmental impacts in use:

* The requirement for a rich burn engine to run at the stoichiometric point means it uses more fuel than a "lean burn" engine running at a mixture of 20:1 or less. This increases the amount of fossil fuel consumed and the carbon dioxide emissions of the vehicle. However, NOx control on lean burn engines is problematic.
* Although catalytic converters are effective at removing hydrocarbons and other harmful emissions, they do not solve the fundamental problem created by burning a fossil fuel. In addition to water, the main combustion product in exhaust gas leaving the engine — through a catalytic converter or not — is carbon dioxide (CO2).[13] Carbon dioxide produced from fossil fuels is one of the greenhouse gases indicated by theIntergovernmental Panel on Climate Change (IPCC) to be a "most likely" cause of global warming.[14] Additionally, the U.S. Environmental Protection Agency (EPA) has stated catalytic converters are a significant and growing cause of global warming, due to their release of nitrous oxide (N2O), a greenhouse gas over 300 times more potent than carbon dioxide.[15]
* Catalytic converter production requires palladium or platinum; part of the world supply of these precious metals is produced near the Russian city of Norilsk, where the industry (among others) has caused Norilsk to be added to Time Magazine's list of most polluted places.[16]


But then there are these ones too.

I'm certainly not saying we should break the law, because that is totally not on. However, it good to know that everything we use to clean something itself has an environmental impact and sometimes that impact out weighs the intended purpose of the cleaning tool.

flat_iv - September 30th, 2010 at 12:02 AM

I dont have to have the cat for emissions. The only reason I was trying it was to cut down on the exhaust noise. Might just try to find a small resornator and weld inplace and remove the cat.

pete wood - September 30th, 2010 at 04:52 PM

a good turbo/bypass muffler might do a better job.

flat_iv - October 5th, 2010 at 12:40 PM

OK, I purchased a pressure guage to measure back pressure. At idle and at 2000 and 4000 rpms it passed with flying colors. Now I am really not sure what is going on. Anyone have a hint of what it might be?

ian.mezz - October 5th, 2010 at 02:25 PM

unbolt the cat and take for a spin, I only ever heard of a block cat or muffler causing a problem

ricola - October 6th, 2010 at 03:19 AM

I had similar symptoms when a cat collapsed internally... At low speed it was fine but anything more and it was gutless...

flat_iv - October 6th, 2010 at 09:18 AM

That is exactly what I am going to do. Cut the cat out and splice in a pipe and reweld. Just to try it.

Joel - October 6th, 2010 at 09:23 AM

If you could see through the cat you may actually have a fuel delivery issue, even if its the ECU going into limp mode cos something has upset it

I know mine with a high flow 2.5" cat and straight through 2.5" turbo muffler felt barely any different when i rung its neck for the sound test by putting a plate with only a 1" hole after the cat as a gasket
It actually had better low down torque
The stock mufflers on the subis are very restrictive to keep them quiet

flat_iv - October 19th, 2010 at 09:18 AM

Something funny was going on with that cat. I cut it out and everything went back to normal.

waveman1500 - October 19th, 2010 at 09:32 AM

Good to hear that you solved the problem.

Pete Wood, there are ways and means to solve most engineering problems. A popular one in modern engines has been to incoporate the cat into the exhaust manifold, only a couple of centimetres away from the head, thus ensuring that it heats up quickly. Some cars also have electrically heated cats to warm them up faster.

You may say that catalytic converters do more harm than good, but let me assure you that even if a catalytic converter caused your car to output significantly more CO2, it would still be worth it's weight in gold. Some of the nastier exhaust emissions gases are many times worse than CO2. For example, over 20 years in the atmosphere a kilogram of methane does the same damage as 72kg of C02. Catalytic converters can change methane and other hydrocarbons into CO2, thus reducing their impact on the environment substantially.