Pro's and Con's of Cat Converters??
12-23-2007, 08:10 AM
#1
Rennlist Member
Thread Starter
Pro's and Con's of Cat Converters??
Just considering some exhaust changes. Possibly 4" Cat back. Just wondering what the general consensus is on running with and without a Cat? How much do they rob flow/power etc? Is it worth running a replaceable Cat for the street and straight through for the track?
Any opinions, advice, experience is fine.
thx
Any opinions, advice, experience is fine.
thx
12-23-2007, 12:03 PM
#4
Race Director
It always varied slightly on different dyno runs, IIRC the power was withing 3 rwhp with or without the cat. It took some time to get the pipes off and weld in cats so the runs were done with slightly different temperatures.
12-23-2007, 12:10 PM
#5
Racer
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That is very interesting. I suppose force induction makes a big difference? Becuase I get the impression from our 951 guys that there is a noticable difference when running without the cat.
12-23-2007, 04:25 PM
#7
Nordschleife Master
This is a great topic that will take a bunch of explaining.
Let me start by saying the only reason to have a catalyst is if you tree hugger. The truth about catalyst is a very complicated one as its not a simple "I have catalyst and I lost no power".
So lets start.
No matter what you do catalyst have a negative effect on your motor. You can spend as much money as you want and get the best catalyst on the market but HP and Engine Longevity will be reduced.
All Catalyst work under the same basic principles in terms of there operation. This means that in order to convert catalyst you need expensive metals and the better the metals the less surface area needed to convert the airflow. As we know more surface area means less flow so we really don't want alot of surface area in our high performance catalyst. So what does this mean? This means we better get expensive metals to convert the air more effectively then a cheaper catalyst. Now, Keep in mind your cheap catalyst bring around $150-$200 at a scrap yard! So, its going to be expensive to get a good high performance catalyst that really uses alot of expensive metals compared to the cheap ones. Now, your thinking you have seen some that are not that expensive. Hey, guess what I have too but they are not going to work like a factory catalyst for many reasons. The first is that they don't have the amount of expensive metals to convert at the rate of the factory unit. Usually you will find they do 1/5th the job. Hey! guess what they have 1/5 the cells makes sense. So now with a 4/5 reduction of environmental friendliness is it still worth it? Well, if you think well ok let me spend alot of money on a good catalyst well thats fine. I agree that you can spend your money to save the environment if you feel its in danger. So, you went out and spent the big bucks on the high doller catalyst that will reduce emissions with all of its expensive metals. However, will it really? Well if you are really a hardcore environmentalist. Then no, it will not do the job you think its going to do and the reason is heat! factory units have more surface area and thus become heated faster. Your new expensive one no matter how good it might be simply will not heat as fast as a cheaper factory one. So you can look past this because this is very small amount and only on startup and you like to drive long distances. Sounds good doesn't it? Well, no simply its not good because remember heat is how a catalyst works right? Well, like sweanders said you don't see a difference on the dyno. Well, that might be true they flow great! but the heat is what will reduce your HP (small amount). The same is true of what this heat can do to your motor and look no further then the Porsche 911. Thats right folks love your valve guides? Well I do too. However, Heat HATES THEM and its out to kill them. So just visit your local pyrogauge for readings and you will find more heat with catalyst. Also, this goes along with my reasoning behind the death of the air cooled motor.
P.S. I don't think I can get my point across in text as it is just to many levels to understand. I could seriously write 100X more and still not cover all the aspects. So let me sum it up that they are not something you want on a performance car and a waste of money.
Let me start by saying the only reason to have a catalyst is if you tree hugger. The truth about catalyst is a very complicated one as its not a simple "I have catalyst and I lost no power".
So lets start.
No matter what you do catalyst have a negative effect on your motor. You can spend as much money as you want and get the best catalyst on the market but HP and Engine Longevity will be reduced.
All Catalyst work under the same basic principles in terms of there operation. This means that in order to convert catalyst you need expensive metals and the better the metals the less surface area needed to convert the airflow. As we know more surface area means less flow so we really don't want alot of surface area in our high performance catalyst. So what does this mean? This means we better get expensive metals to convert the air more effectively then a cheaper catalyst. Now, Keep in mind your cheap catalyst bring around $150-$200 at a scrap yard! So, its going to be expensive to get a good high performance catalyst that really uses alot of expensive metals compared to the cheap ones. Now, your thinking you have seen some that are not that expensive. Hey, guess what I have too but they are not going to work like a factory catalyst for many reasons. The first is that they don't have the amount of expensive metals to convert at the rate of the factory unit. Usually you will find they do 1/5th the job. Hey! guess what they have 1/5 the cells makes sense. So now with a 4/5 reduction of environmental friendliness is it still worth it? Well, if you think well ok let me spend alot of money on a good catalyst well thats fine. I agree that you can spend your money to save the environment if you feel its in danger. So, you went out and spent the big bucks on the high doller catalyst that will reduce emissions with all of its expensive metals. However, will it really? Well if you are really a hardcore environmentalist. Then no, it will not do the job you think its going to do and the reason is heat! factory units have more surface area and thus become heated faster. Your new expensive one no matter how good it might be simply will not heat as fast as a cheaper factory one. So you can look past this because this is very small amount and only on startup and you like to drive long distances. Sounds good doesn't it? Well, no simply its not good because remember heat is how a catalyst works right? Well, like sweanders said you don't see a difference on the dyno. Well, that might be true they flow great! but the heat is what will reduce your HP (small amount). The same is true of what this heat can do to your motor and look no further then the Porsche 911. Thats right folks love your valve guides? Well I do too. However, Heat HATES THEM and its out to kill them. So just visit your local pyrogauge for readings and you will find more heat with catalyst. Also, this goes along with my reasoning behind the death of the air cooled motor.
P.S. I don't think I can get my point across in text as it is just to many levels to understand. I could seriously write 100X more and still not cover all the aspects. So let me sum it up that they are not something you want on a performance car and a waste of money.
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12-23-2007, 04:57 PM
#9
Rennlist Member
Thread Starter
Thanks F-man, but my only reason for making inquiries is that in Australia cops have the ability to pull you over and if they see that it's a modified car ie larger exhaust, they can take you to the 'Sniffer' and shove something up it's **** like Dr Procter, and if you have high Co2 readings or whatever, they can issue us with a fine up to something stupid like $25k (that's probably an extreme amount that they'd never do, but you get the point). So what you're saying is that no matter what aftermarket Cat we get, it's still not going to reduce the emissions enough to pass the 'Sniffer' test anyway? What about the flames that come out too? They would be a nice little flag for the cops to check me out. Would the Cat tame these? What about a removable Cat, bolt in/unbolt for track type of setup? This company seems to shout out pretty loud about the quality of their product, still not worth it? http://www.metalcat.com.au/
I'm not trying to save the planet, just my ***. If it's really not worth it then I won't bother.
I'm not trying to save the planet, just my ***. If it's really not worth it then I won't bother.
12-23-2007, 05:20 PM
#13
Rennlist Member
Thread Starter
The question has arisen not because you get a nice letter in the mail saying it's time for your yearly check up. We can get stopped randomly on the street and tested. That is why I'm asking about the characteristics of the Cat. I don't want to run one but I don't want a massive fine either.
Why is it affected so much by race fuel?
Why is it affected so much by race fuel?
