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Location: North Sydney
Registered: May 2002
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Catalytic converters a restriction or not?
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Fri, 27 September 2002 03:04
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There's been a few discussions on whether they are restrictive or not.
Some people think they dont pose a restriction on a street car.
I dont understand how they could flow as well as a straight pipe, maybe the ones these guys use have an internal blower to up the flow rate??????
I had a restriction in my exhaust which we weren't sure where it was. We temporarily removed the cat and put in a straight piece of pipe and saw a 30rwhp increase with no ECU changes except for adjusting a/f ratios to bring them back to setpoint. They were leaner after changing the cat cause it was flowing better. That in itself indicates its a restriction.
What do you guys think?
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I supported Toymods
Location: Perth
Registered: May 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 03:30

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I've got no doubt now that they are a restriction. I still think they are a damn good idea. The shit that is formed when unleaded fuel is burnt, especially the higher octane brews, is just nasty.
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Location: Lost in the K hole
Registered: May 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 03:40

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no cat = 10kmh extra down the straight of eastern creek
BUT
no cat = cancer
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I supported Toymods Banned User
Location: Brisbane
Registered: May 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 03:49

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Barnes Performance Dyno Tune
07 5441 7700
Stock ST205 3S-GTE and 3 1/4 exhaust system, remove the high flow approved cat converter, fit straight throuh pipe = No gain on the dyno at all!!! Believe it or not!
This test was preformed at the above place.
Knowledge is one thing, experience is another
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I supported Toymods
Location: Berowra-Sydney
Registered: July 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 04:12

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you would have to be the most stupid idiot on the face of the earth if you thought placing something in the exhaust system which the air has to push its way through isn't going to be restrictive.
any bend in the exhaust system is going to supply some form of restriction so of course a cat which air has to push its way through is going to make a restriction.
physics people physics,
only way it wont make a restriction is if the cat had a better or exactly same flow rate as a piece of exhaust pipe.
also think of the turbulence created from the air trying tp push through all those holes and plates
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Location: South Australia
Registered: July 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 04:40

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Catalytic converters are a restriction, but I seriously doubt that you'll see a huge difference in power figures with or without one...unless 3-5hp is a big difference to you.
I would personally keep a catalytic converter on a car, because on the rally track, 3-5hp at the very high end of your revs (where you spend little time anyway) is such a ridiculous thing to bother with at the expense of health/environment. For a road car, you'd have to be a bit of a *you know what* to take it off.
If anything, just get a good high flow cat converter.
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Location: Southern Sydney
Registered: August 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 06:40

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Believe it or not Catalytic converters do more harm to the environment than they do good.....
Now before the comments start flying hear me out.
Catalytic converters contain a very rare metal inside them that splits up some of the nasty exhaust bits and neutralise's some bad stuff. I won't get technical here... if you want to know more there is heaps of stuff available on the web on it.
The reason Cats are so expensive is because how rare and hard to get these precious metals are....
Now I'm not arguing that cats don't perform a good job. They work very effectively at performing their role and do reduce exhaust emissions..... BUT.... the amount of mining and crap that goes on to get these metals is causing thousands of times the damage as the exhaust emissions.
The metals are only found in like 3 countries around the world... can't remember which ones but I think they were all around Africa.
I read this on a scientific website which had actually calculated the damages caused and they worked out we would be much better off if Cats had never been introduced....
Theres some food for thought.
If I can find the link I'll post it... I'm not real hopeful though
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I supported Toymods
Location: Perth WA
Registered: May 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 08:32

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I think that the platinum / palladium in the cats are one part of the car that is almost always recycled, so hopefully over many years the need for new mining is decreased.
The most important and perhaps selfish reason for cats is that they reduce the pollution in your home town, but the mining roots up some African country (!!) - pollution shifting.
I'd always run a cat because of the strict penalties ($1,000's ?) for polluting the environment (and also it seems the "green" thing to do). I plan to keep my car going for a long time to reduce the need for mining new metals for new cars.
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Registered: July 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 19:45

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If I imagine the restriction of the cat. in "physical" term, the honeycomb of the cat converter seems to have the same structure as 100x 10 Ohm resistor in an electrical circuit, how much resistance? Probably the same resistance as the copper wire itself..
If you try to blow through a pipe with 2 or 3 45degree bends, you may feel some restriction, but if you stuff 30 or 40 straws (drinking straws) in your mouth and blow, it's pretty hard to imagine any restriction..
Probably the only time when you will gain significate hp by removing the cat., is when your cat. has been stuffed with carbon deposits throughout its usage, thus causing the restriction, if the exhaust system is 3 inch I.D. and the cat. is 3.5 inch I.D. the bigger cross section probably already made up for the restriction anyway..
But I think the most important job of the cat. converter is removing the carbon monoxide (CO) which will make you tired, sleepy, headache, and will kill you if the concentration is high enough, so think about what you're breathing when you reverse your car, or when you're stopping in traffic as your exhaust can be blown back inside your car..
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Location: North Sydney
Registered: May 2002
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Re: Catalytic converters a restriction or not?
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Fri, 27 September 2002 23:31
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Well i have no doubt in the world they pose a restriction. I just wanted to see if others weren't as naive as some.
I put my car on the dyno before the last dyno day and had 270rwhp. It was ok but you could hear something choking the car in the exhaust. It's a 3inch custom made job with mandrel bends custom dump pipe(the factory ct26 is crap) and straight through muffler. It has a proper 3inch hi-flow cat.
We decided that it could only be the cat causing a restriction so we removed it and put in a straight pipe temporarily. We had to re-adjusting the a/f ratios because the car was flowing so much better it ran leaner. This would indicate to anyone right there that it is definitely posing a restriction. So i knew the next power run would definitely be a good increase.
Well, 270rwhp>>>>>300rwhp. A very healthy increase, and no ignition timing was added which is where big hp increases can normally be seen.
Thats enough for me, also the fact that by simply looking at it will tell you when a 3lt engine with 14 pounds of boost at 6000 rpm is pumping so much air it will be a restriction.
When you have your car flowing air really really well, the smallest restriction will become a massive restriction when the rest is flowing so well. Also i might add my cat is in perfect condition, no blockages etc.
On a standard car you might not see much of a difference but there would be some.
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