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jmstr
Dodge Dakota
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11/24/2003
18:26:24
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 Subject: Exhaust flow through Cat Conv?
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I have done a lot of reading of the posts on this site to help me make some decisions about the exhaust setup for my 97 v6 Dak. One thing that I think I read somewhere, but can't remember if I did or I dreamt it, had to do with the catalytic converter. Can someone help me here? From what I think I remembered reading any muffler system that produces an exhaust flow over 410 cfm is pretty much useless. Is this right?
The reason for this question has to do with the catalytic converter as the 'bottle-neck' in the flow of exhaust. From what I have read, most 'hi-flow' cats only have an exhaust flow of around 400 cfm. Thus the whole arguement of having a muffler with only 400 cfm versus a 1000 cfm muffler [DynoMax SUper Turbo versus their UltraFlo, or a Flowmaster] is useless in a state like mine that requires the cat to be there. If the cat will only allow 400 CFM to leave it, why would it matter that one muffler allows two times that amount of exhaust flow: it isn't going to happen.
Or am I thinking of a dream rather than factual information?
thanks!
jason
97 v6 clubcab
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slow r/t man
Dodge Dakota
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11/24/2003
18:55:34
| RE: Exhaust flow through Cat Conv?
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Your stock muffler has more restriction than your catalitic converter. Why does everyone villify these things? You may gain a few horse power at red line if you remove it. I don't think its worth
the hassle for an engine under 275 HP. Besides alittle back pressure will make it run better.
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capone
Dodge Dakota
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11/24/2003
18:59:07
| RE: Exhaust flow through Cat Conv?
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I'm not sure about the post you are talking about, but I
think I have an idea about the cat.
The muffler provides resistance either way, no matter how
much air leaves the cat. I'd imagine that the higher the
airflow for the muffler the better, because even if there isn't
a lot of air going through the cat, it will still be slowed
down through the muffler. I'm not sure about anything
over 410 not being effective, because I've heard of people
removing the cat all together and it still gives a huge power
increase.
I'm just speculating, i'm not an exhause expert or anything,
but I hope this helps some.
-capone
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i saw
Dodge Dakota
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11/24/2003
19:08:04
| RE: Exhaust flow through Cat Conv?
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i saw a posting on here before that someone said that a study they had seen in hot rod or sport truck or some magazine like that showed a comparison between a engine with a factory cat and on without. On the dyno with the cat the engine produced a mere 1.8 hp. less then a straight pipe setup did. thats right 1.8 hp. and at peak torque the thing actually produced 2 ftlb LESS with the straight piped then the cat installed, thats right remove the cat and LOOSE torque. The end result is this, you gain maybe 1/2 mile per hour in top speed that you will never see due to the built in rpm limiter on your PCM and it will take you just about .008 seconds LESS to reach that speed.
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jmstr
Dodge Dakota
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11/24/2003
19:33:54
| RE: Exhaust flow through Cat Conv?
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Thanks for such quick responses. I am not overly worried about the ultimate potential horsepower and torque, as I could just by the same truck in 5.9L and have a big jump already. Where I live I can't remove the catalytic converter, as Southern California is about as anal as they come when it comes to this stuff. So, since the existence of the Cat has to be a given [and I will be replacing the factory OBD II with an aftermarket OBD II Cat, as the factory has seperated inside], the question I have is "will there truely be a significant change in power by adding a really high-flowing muffler [say, the Dynomax UltraFlo at about 1100CFM] after the catalytic converter [has to remain installed] versus a lower volume [say DynoMax SuperTurbo @ 410CFM, or Flowmaster 50 series @ 370CFM]"?
I know that the factory muffler is a huge example of inefficiency in design from a power point of view, and that any of these will give me a jump in power. Since the cat has to be installed, the real question boils down to "will the only difference I experience in these mufflers be primarily sound"? Or, am I wrong in my thoughts/observations of the CFM flow of catalytic converters being 'capped' at around 400CFM? Thanks and keep up the comments, this IS helpful!!!!
jason
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slow r/t man
Dodge Dakota
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11/24/2003
22:17:22
| RE: Exhaust flow through Cat Conv?
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You hit the nail on the head "the only difference you will notice is sound" CFM ratings mean absoltutely nothing unless they are all done on the same equiptment and about 10 other factors I don't even know what they are. Manufacturers are advertising with big cfm #s for 1 reason, guess what it is...........
Don't fall for that.
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slow r/t man
Dodge Dakota
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11/24/2003
22:17:22
| RE: Exhaust flow through Cat Conv?
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You hit the nail on the head "the only difference you will notice is sound" CFM ratings mean absoltutely nothing unless they are all done on the same equiptment and about 10 other factors I don't even know what they are. Manufacturers are advertising with big cfm #s for 1 reason, guess what it is...........
Don't fall for that.
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