Okay so I did some searching on here before I started this thread. I was not able to find an answer to my question. So here it is.. and hopefully you guys can help me out cus im new here. I have a 91 civic si with the d16.. I just put on a 4-2-1 dc sports header, and a cat back skunk 2 exhaust.. What should I run for the cat? Should I run a test pipe from skunk 2 or any generic brand, or actually buy a high flow cat from magnaflow or any generic brand. Please inform me. I dont really want a back firing crackle sound when I let off the gas. So what would the difference between the two make?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eckoplayr &raquo;</TD></TR><TR><TD CLASS="quote">Okay so I did some searching on here before I started this thread. I was not able to find an answer to my question. So here it is.. and hopefully you guys can help me out cus im new here. I have a 91 civic si with the d16.. I just put on a 4-2-1 dc sports header, and a cat back skunk 2 exhaust.. What should I run for the cat? Should I run a test pipe from skunk 2 or any generic brand, or actually buy a high flow cat from magnaflow or any generic brand. Please inform me. I dont really want a back firing crackle sound when I let off the gas. So what would the difference between the two make?</TD></TR></TABLE>don't pay extra for a "high flow cat" it's the same thing as a regular cat. I don't know what the sound difference would be since I've never driven without a cat on. But, if you have to take any kind of emissions testing in your state, I would keep a cat on there.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ILcrxsi1 &raquo;</TD></TR><TR><TD CLASS="quote">don't pay extra for a "high flow cat" it's the same thing as a regular cat. I don't know what the sound difference would be since I've never driven without a cat on. But, if you have to take any kind of emissions testing in your state, I would keep a cat on there.</TD></TR></TABLE>

Yes, you're a jackass.

I have an A6 with I/H/E
Get the magnaflow.
1) It flows better and sounds nice. (deeper and not raspy)
2) My gas mileage went up 2.5 miles per gallon VS. stock cat.
....and the old one was still good, so the "it was probably worn out or plugged up"
.....arguement won't work.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SIred91 &raquo;</TD></TR><TR><TD CLASS="quote">

Yes, you're a jackass.

I have an A6 with I/H/E
Get the magnaflow.
1) It flows better and sounds nice. (deeper and not raspy)
2) My gas mileage went up 2.5 miles per gallon VS. stock cat.
....and the old one was still good, so the "it was probably worn out or plugged up"
.....arguement won't work.</TD></TR></TABLE>If you actually think there is going to be a flow difference from one honeycomb cat to another than you're the jackass.

 

Especially if you think a difference in design would be enough to actually affect an a6.

 

But then again if the "high flow" cat costs less just get that, because it's the same damn thing anyway.

 

Oh, little baby boy get butt hurt?

Go cut one of each open and then come back with an answer.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SIred91 &raquo;</TD></TR><TR><TD CLASS="quote">Oh, little baby boy get butt hurt?

Go cut one of each open and then come back with an answer. </TD></TR></TABLE>I don't need to, since your a6 went so much faster with a high flow cat. I bet you had trouble hooking up after that mod huh? Did you break any windows with the sonic boom. You know I'm right.

 

Your a funny guy. Srsly. I did it for the gas mileage, hero.

I have NEVER told anybody that my crx is even quick. Its almost bone stock, cupcake.

 

Cupcake, nice. You can always do my patented cat mod . . . have your distributor fail at highway speed. As you punch the throttle trying to figure out what is going on, and your engine gradually bogs down to zero RPM, and your sled starts coasting, buckets of uncombusted fuel wil slosh down that header and hit the cat, at which point you just let chemistry do its thing. Don't mind the cabin smoke, BTW, just open the windows and wait for the fire to burn out all the oxygen left in your exhaust.

When you're done, you should have a nice "high flow" cat that looks completely stock. Have fun!

Peace
policy

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by policyvote &raquo;</TD></TR><TR><TD CLASS="quote">Cupcake, nice. You can always do my patented cat mod . . . have your distributor fail at highway speed. As you punch the throttle trying to figure out what is going on, and your engine gradually bogs down to zero RPM, and your sled starts coasting, buckets of uncombusted fuel wil slosh down that header and hit the cat, at which point you just let chemistry do its thing. Don't mind the cabin smoke, BTW, just open the windows and wait for the fire to burn out all the oxygen left in your exhaust.

When you're done, you should have a nice "high flow" cat that looks completely stock. Have fun!

Peace
policy

</TD></TR></TABLE>

Holy ****, I just laughed myself off of my chair remembering almost that exact same thing happening to me two months ago. HAHAHAHAHAHA.....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SIred91 &raquo;</TD></TR><TR><TD CLASS="quote">Your a funny guy. Srsly. I did it for the gas mileage, hero.

I have NEVER told anybody that my crx is even quick. Its almost bone stock, cupcake.</TD></TR></TABLE>And I'm sure you keep a log of your driving style and every time that you fill up, I mean you must have to to come to the conclusion that you get "2.5" mpg more now than you did before when you had that pesky low flow cat. Either that or your full of ****

 

I do in fact keep a log of the mileage in this car.

What is your problem Nancy? Well, other than being a self admitted jackass.

 

"MagnaFlow Performance Exhaust High Flow Catalytic Converters are designed for optimum flow. The converters feature a stainless steel body and a bright mirror finish stainless steel heat shield. They contain a flow efficient ceramic catalyst, ribbed body for strength and a funnel inlet and outlet for smooth exhaust flow."

Straight from the horses mouth. Do you want to explain to me how one ceramic honeycomb cat can flow better than another ceramic honeycomb cat? Better let lets hear your explanation of the difference between a high flow car and a regular cat, since you're an expert.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SIred91 &raquo;</TD></TR><TR><TD CLASS="quote">

What is your problem Nancy? Well, other than being a self admitted jackass.</TD></TR></TABLE>knightsport game me that title. It was more out of love than anything . I have no hang-ups about my HT title. Especially not when dealing with a fool like you.

 

Haha....re-read the thread son.

 

I can't say for sure about any other high flow cat, but the magnaflow has two biscuits instead of one inside it. spaced apart. The shape of the honeycomb is in fact, different than a stock cat. It has larger holes as well.
The second and most effective difference is the shape of the can itself. It has a smaller overall diameter so that the gasses do not have enough room to swirl around and create back-pressure, they flow straight through.

Do you need a lesson on back-pressure as well?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SIred91 &raquo;</TD></TR><TR><TD CLASS="quote">I can't say for sure about any other high flow cat, but the magnaflow has two biscuits instead of one inside it. spaced apart. The shape of the honeycomb is in fact, different than a stock cat. It has larger holes as well.
The second and most effective difference is the shape of the can itself. It has a smaller overall diameter so that the gasses do not have enough room to swirl around and create back-pressure, they flow straight through.

Do you need a lesson on back-pressure as well?</TD></TR></TABLE>Most cats have a space in the middle between two seperate honeycombs you moron. Show me this ground breaking new honeycomb design. And I just read the magnaflow website and it says nothing about a smaller overall diameter. In fact it says it's exact oem specifications.

 

Not that any of this argument even matters because I checked the price and a magnaflow cat is cheaper than a cat from pep boys so what the hell why not. But I guarantee you that if they flow any better at all it's going to be miniscule and you're not going to see a difference.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ILcrxsi1 &raquo;</TD></TR><TR><TD CLASS="quote">Most cats have a space in the middle between two seperate honeycombs you moron. Show me this ground breaking new honeycomb design. And I just read the magnaflow website and it says nothing about a smaller overall diameter. In fact it says it's exact oem specifications.</TD></TR></TABLE>

Oem specs in leangth yes. And if you have a degree in mechanical engineering and engine theory like me, you will understand that size does in fact matter, and that there are also choices in the cat you can purchase.

The honeycomb in a stock cat swirls if you cut the thing apart and look at it.
The magnafow does not twist nearly as much.

So, you are probably one of those kids that thinks a honda needs backpressure to have torque too aren't you?

 

If your car is in as good as shape as mine is, you WILL see a difference. In your gas mileage.

And just to help you a little more, here is a little something to read.
One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Hondas need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory

Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity

Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.
The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.
Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?

I often wonder how the myth "Hondas need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?

The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).

VI. Conclusion.

SO it turns out that Hondas don't need backpressure, they need as high a flow velocity as possible with as little backpressure as possible.

 

My pep boys cat has two seperate honeycombs also is it high flow. I'm just going to have to believe that the last thing you said is bullshit also, since I doubt that you have cut your magnaflow cat open.

 

Not to interfear with your arguments.. its very amussing say the least lol...but i guess im looking for more people have done the mod.. so can verify rather its going to sound like crap or not.. I dont have any emission testing hear.. i just want the exhaust to sound good.. not a backfireing pos.. so basically should I run a cat or not should be the question I should of asked.. I threw the stock one away so .. no going back to that money is not an issue... i just need to know what to put in place of the stock cat cus now i have a dc sports 2 peice header and a full cat back skunk 2.. sorry if I mislead the question

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eckoplayr &raquo;</TD></TR><TR><TD CLASS="quote">Not to interfear with your arguments.. its very amussing say the least lol...but i guess im looking for more people have done the mod.. so can verify rather its going to sound like crap or not.. I dont have any emission testing hear.. i just want the exhaust to sound good.. not a backfireing pos.. so basically should I run a cat or not should be the question I should of asked.. I threw the stock one away so .. no going back to that money is not an issue... i just need to know what to put in place of the stock cat cus now i have a dc sports 2 peice header and a full cat back skunk 2.. sorry if I mislead the question </TD></TR></TABLE>shut up

Nice article that you posted above, but it says nothing about the topic at hand. I never said that I don't understand back pressure or velocity. We are talking about high flow cats here and how they are the same thing as a normal cat.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ILcrxsi1 &raquo;</TD></TR><TR><TD CLASS="quote">shut up

Nice article that you posted above, but it says nothing about the topic at hand. I never said that I don't understand back pressure or velocity. We are talking about high flow cats here and how they are the same thing as a normal cat.</TD></TR></TABLE>

And? That article, by the way, has everything to do with this discusion.
The Magnaflow cat, and ANY other cat made like it, help velocity, and pressure, so yeah, anyway......

To the OP, the magnaflow helps with the sound of the exhaust. It will be a little deeper, and not raspy at all. But also run a resonator as well.