High Flow Cat

How much does a good high flow cat help? HP wise? Are they worth the money, also which brands are the best?

I'm sure they'll give you decent gains when paired up with a catback. Personally, i'd go ahead and get a test pipe and just put the stock cat back on when smog time comes around. Anyway, for the high flow cats i'd go with Random Technology or CarSound.

every manufacturer and car enthusiast that ive talked to says that u will see minimal to no gains and are basically a crock of shit so if i were u id save that money and just leave ur stock cat on and get i high performance exaust system. Skunk2 has some pretty nice ones.

i have an aftermarket cat back right now, how much would a cat cost and how much for install , how much hp gain , maybe 3, 4 , 5?

every manufacturer and car enthusiast that ive talked to says that u will see minimal to no gains and are basically a crock of shit so if i were u id save that money and just leave ur stock cat on and get i high performance exaust system. Skunk2 has some pretty nice ones.

Yeah unless you have turbo, high flo cats don't do much. Some people even say that it reduces power because the engine requires a certain amount of back pressure.

thanks for the imput guys, i dont think im going to buy one

it all depends on the size of inlet and outlet you use and how much hp you have determines what size you do use...if you choose the right one combined w/ a full header back exhaust system you'll see some gains...it will be better than stock. think about it like this...when you cut off your cat then you get more power right? well why wouldnt a high flow cat not be better? its just one step closer to not having the cat there. you'll see some gains

but in the same way you'll lose power if you pick the wrong one...just like if you put saya 3in exhaust system on a car w/ like 120 hp...youre ognna lose power...put that same 3 in on a 200-250 hp car and you gain power...just dont pick one too small or too big

Yeah unless you have turbo, high flo cats don't do much. Some people even say that it reduces power because the engine requires a certain amount of back pressure.

Power gains/losses have nothing to do with backpressure. Backpressure is NEVER a good thing.

Power gains/losses have nothing to do with backpressure. Backpressure is NEVER a good thing.

Actually backpressure helps develop more torque on the low end...but you'll lose top end horsepower. With less backpressure you make more hp at higher revs, but it takes forever to get there because the low end has no torque.

No. Myth. Backpressure is NEVER good. Look it up.

You don't want backpressure. What you DO want, is exhaust velocity. Hence N/A applications generally using 2.25 Piping, and FI applications generally use 2.5-3.0 piping.

http://www.automotiveforums.com/vbulletin/showthread.php?t=13199

I've been looking for information to quantify what "high flow" means. I've yet to find numbers that tell the cfm or backpressure for any particular cat provider. I suspect that they are all pretty much the same. Most seem to have 400 cells per inch (I think that is measured in surface area), but are sketchy on how many inches the gas must flow through before exiting. Some supposedly opnly have 200 cells per inch, but have thicker cell walls so you may wind up with the same amount of "open" area. In addition, some cat makers use one large "brick" and others use 2 smaller ones. Lastly, they can coat them in different metals. Has anybody found one place that lays all the alternatives out?

A manufacturer can slap on the term 'high flow' as long as it is less restrictive than the stock unit. Often times, this noticeable increase in flow is due to the residue left in the catalytic converter from incomplete combustion moreso than the unit itself. A high flow cat does not produce significant power gains on its own.

I say stick with the stock catalytic converter or replace it with a new unit and do mother nature a service.

You don't want backpressure. What you DO want, is exhaust velocity. Hence N/A applications generally using 2.25 Piping, and FI applications generally use 2.5-3.0 piping.

t=13199[/url]

thats assuming youre using manderal bent piping correct? non manderal bent you want to upsize that .25 to .5 inches??

No. Myth. Backpressure is NEVER good. Look it up.

You don't want backpressure. What you DO want, is exhaust velocity. Hence N/A applications generally using 2.25 Piping, and FI applications generally use 2.5-3.0 piping.

http://www.automotiveforums.com/vbulletin/showthread.php?t=13199
I did look it up - pay close attention to what I said, and read the last sentence of the following quote:

"We know that exhaust gas is actually a series of pulses, we can use this knowledge to propagate the forward-motion to the tailpipe. How? Ah, more of the engineering tricks we are so fond of come in to play here.

Just as Paula Abdul will tell you that opposites attract, the low pressure tail end of an exhaust pulse will most definitely attract the high-pressure bow of the following pulse, effectively "sucking" it along. This is what's so cool about a header. The runners on a header are specifically tuned to allow our exhaust pulses to "line up" and "suck" each other along! Whoa, bet you didn't know that! This brings up a few more issues, since engines rev at various speeds, the exhaust pulses don't always exactly line up. Thus, the reason for the Try-Y header, a 4-into-1 header, etc. Most Honda headers are tuned to make the most horsepower in high RPM ranges; usually 4,500 to 6,500 RPM. A good 4-into-1 header, such as the ones sold by Gude, are optimal for that high winding horsepower you've always dreamed of. What are exhaust manifolds and stock exhaust systems good for? Besides a really cheap boat anchor? If you think about it, you'll realize that since stock exhausts are so good at restricting that they'll actually ram the exhaust pulses together and actually make pretty darn good low-end torque! Something to keep in mind, though, is that even though an OEM exhaust may make gobs of low-end torque, they are not the most efficient setup overall, since your engine has to work so hard to expel those exhaust gasses."

Remember I said backpressure is good for low end torque but not for high revs? Trust me, I've run my car with no exhaust, top end felt faster and the bottom end of the RPMs sucked. Put the exhaust back on and bottom end returned, but top end felt more restricted.

The myth is that backpressure makes horsepower, it doesn't. The fact is that backpressure makes more torque available at low rpms (it doesn't make more torque overall, it just makes torque available sooner). Dyno it and see for yourself.

Of course none of it means shit if you're planning on driving your car WOT and at redline all the time.

The myth is that backpressure makes horsepower, it doesn't. The fact is that backpressure makes more torque available at low rpms (it doesn't make more torque overall, it just makes torque available sooner). Dyno it and see for yourself.

Backpressure makes nothing. Backpressure is never good. Backpressure is never good. Backpressure is never good.The article below, is just for you. Since you believe that backpressure makes low end torque.

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

Particularly, some people equate backpressure with torque.....The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture,

Now that we have established that backpressure does not equate to torque. Let's examine the definition of backpressure.

BACKPRESSURE: Resistance to air flow; usually stated in inches H2O or PSI.

Obviously, you want your exhaust to be as free flowing as possible, so why would you want backpressure (resistance to the free flow)?

To remove this resistance (backpressure) of course, you up the size of your exhaust piping. For example in an N/A application, to 2.25 inches.

And so one, might argue, "Well, if a free flowing exhaust is so good Mr. Smartass, why don't you just go with a 5 inch exhaust!? HAH! SEE! You'd lose torque because theres no backpressure!"

Untrue. By increasing the size of the piping you remove backressure. But when you increase the size of the piping too much, you lose exhaust velocity; which is the reason for the "gutlessness" of your low end.

Backpressure is never good. What you want, is proper exhaust velocity.

Untrue. By increasing the size of the piping you remove backressure. But when you increase the size of the piping too much, you lose exhaust velocity; which is the reason for the "gutlessness" of your low end.


"Proper exhaust velocity" implies a tuned exhaust, which by definition requires some backpressure.

I agree with you that loss of exhaust velocity induces gutlessness on the low end. What I am saying is removing backpressure entirely causes loss of exhaust velocity (on the low end).

But let's just agree to disagree about this - I really don't want to have a "war of the informational internet links" thread.

is that not an oxymoron?? "removing backpressure entirely causes loss of exhaust velocity (on the low end)"

so in essence you're sayin if you have backpressure you will have more exhaust velocity at lower end...how is that possible considering backpressure is exhaust moving towards the engine and exhaust velocity is how fast the exhaust is moving away from the engine....sort of like sayin if you run a 4 min mile w/ no wind in your face and then you add a 30 mph wind in your face then you will run it faster?...not gonna happen

so in essence you're sayin if you have backpressure you will have more exhaust velocity at lower end...how is that possible considering backpressure is exhaust moving towards the engine and exhaust velocity is how fast the exhaust is moving away from the engine....sort of like sayin if you run a 4 min mile w/ no wind in your face and then you add a 30 mph wind in your face then you will run it faster?...not gonna happen

Thank You.

is that not an oxymoron?? "removing backpressure entirely causes loss of exhaust velocity (on the low end)"

so in essence you're sayin if you have backpressure you will have more exhaust velocity at lower end...how is that possible considering backpressure is exhaust moving towards the engine and exhaust velocity is how fast the exhaust is moving away from the engine....sort of like sayin if you run a 4 min mile w/ no wind in your face and then you add a 30 mph wind in your face then you will run it faster?...not gonna happen

Please try to correctly understand what I have written, maybe this will help...

Let's say your exhaust is perfectly tuned to have zero backpressure yet still maintain proper exhaust velocity at 3000rpm. You'll still have backpressure when you rev to 9000rpm...

Now let's say you tune your car perfectly to have absolutely zero backpressure and perfect exhaust velocity at 9000 rpm, do you think it's still perfectly tuned when it's running at 3000 rpm? No, it isn't...you'll lose exhaust velocity on the bottom end (your car will sound like it has asthma - struggling to inhale quicker because it's exhaling too damn fast).

My point (for the second or third time), is you can't COMPLETELY eliminate backpressure without affecting the lower rpms.

Obviously you're going to lose velocity when you bring the engine down to a lower RPM point, there's less air volume. I get the impression that you're trying to imply that there is a single ideal exhaust velocity, which is simply not the case.

Ultimately, pressure difference is what creates power. With a properly tuned exhaust, the flow should be travelling one direction all the time... When you reduce the volume (lower the RPM's), the exhaust temperature (and therefore the volume) will decrease, lowering the velocity. This doesn't necessarily mean you're creating backpressure.

Properly tuning exhaust becomes a balancing act in this respect. Piping too small will give you backpressure, and piping too large will drop your velocity.

Exhaust systems use an effect called "scavenging" to create power. Exhaust comes out in pulses and scavenging uses the low-pressure part of an exhaust pulse to pull the higher presser exhaust pulses behind it. This holds true at whatever rpm the engine is running at. If the pipe is too big, the scavenging effect is lost. Like hyperionjza80 said there is no single ideal exhaust velocity. The less rpms the less velocity...the more rpms the more velocity but whether youre at low or high rpms you want zero backpressure. You just want to make sure you dont have an oversized pipe so the scavenging effect will start to take place at the earliest rpms possible. Over size the pipe and you will have the effect but not until a higher rpm...that doesnt mean you have back pressure it just means that the pulses do not have a high velocity so there is less power made at lower rpms. Less power that is causes by oversizing pipe...not in any way b/c of backpressure.

Exhaust systems use an effect called "scavenging" to create power. Exhaust comes out in pulses and scavenging uses the low-pressure part of an exhaust pulse to pull the higher presser exhaust pulses behind it. This holds true at whatever rpm the engine is running at. If the pipe is too big, the scavenging effect is lost. Like hyperionjza80 said there is no single ideal exhaust velocity. The less rpms the less velocity...the more rpms the more velocity but whether youre at low or high rpms you want zero backpressure. You just want to make sure you dont have an oversized pipe so the scavenging effect will start to take place at the earliest rpms possible. Over size the pipe and you will have the effect but not until a higher rpm...that doesnt mean you have back pressure it just means that the pulses do not have a high velocity so there is less power made at lower rpms. Less power that is causes by oversizing pipe...not in any way b/c of backpressure.
All facts that are true and we all agree on...you are merely repeating what has already been posted...and still missing my point, which I will repeat for the fourth or fifth time (and last time, since we are all in agreement but just not understanding each other).

My Point, for the last time...

you can't COMPLETELY eliminate backpressure without affecting the lower rpms.

I still don't understand your argument about low RPM's and torque being affected.

Just as an example, my grandparents have a tractor that utilizes a turbocharger for exhaust scavenging, and that engine has a shit-ton of torque, but no top end. I doubt there's any backpressure in there...

im repeating facts that are not all agreed on or obviously you would understand...the loss of exhaust scavenging is usually thought of as backpressure at low rpms by people who have been informed w/ wrong or atleast not 100% correct information. the loss of scavenging is cause by piping to large for the low rpms youre running at. Yes i may have missed your point but thats b/c you dont have a point...liked you stated earlier we are just going to have to agree to disagree. Maybe one day someone will explain to you in a way you will understand....back pressure sucks and if you have it you're losing HP and torque, no matter what RPM you are at.

Yes i may have missed your point but thats b/c you dont have a point.

This proves you are not comprehending what I have written in very plain english - my point was very clearly stated several times (read the last line of my previous 2 posts)...it is not only my point but a simple fact. If you still don't know what point it is I'm talking about, learn to comprehend better - Hooked on Phonics is helpful for that if I'm not mistaken (I will admit my post got too wordy - you had to comprehend EACH word and its context).

I understand everything you have stated - it is very simple to comprehend because you have re-written what was already posted. I am not arguing about what causes backpressure, I am not arguing about your definition of what backpressure is...I am simply stating what will happen when ALL backpressure is removed.

Also - try to calm down dude, you're obviously getting upset over a stupid arguement about exhaust!

I must say that I have never really agreed completely with that exhaust article found in the tech section. While this may be attributed to me not thoroughly reading the article, I will digress.

I will agree with Gohan Ryu; fast moving exhaust waves inherently create pressure. To eliminate any sort of pressure at all would be, in essence, to stop the exhaust pulses completely. Just like a fan that blows in your face creates pressure, if you turn this fan off, there would be none. If you have zero pressure in your exhaust, your engine would not be running. Take for example top end power. At high rpms, exhaust gases are moving so quickly that pressure/velocity is at its greatest. When you make the exhaust piping larger in this situation, the engine undoubtedly generates more power - there is no pressure to slow it down!

The best exhaust system would be no exhaust; but this creates an inscrutable car that has such absurdly low end that acceleration would be comparable to a Metro. Top end would be spectacular...

ok i may have misworded that...you dont have a point...you have an opinion. im not getting pissed over a lil arguement about exhaust...if you want to talk about someone who is repeating what has already been said look no further than yourself...everything you have said had been the same thing youve said since the beginning. Not saying i havent b/c i have just in a differennt way to help you understand just as youre saying everything over and over in a different way trying to get me to understand. Youre telling me to calm down about the "exhaust arguement" but youre going to say some off the wall comment about my intelligence. "If you still don't know what point it is I'm talking about, learn to comprehend better - Hooked on Phonics is helpful for that if I'm not mistaken"

w/ the "off topic" comments takin care of i guess its my turn to "repeat" myself

when you replace your stock exhaust system w/ a better exhaust system you gain power...agreed. the reason is b/c stock is so restrictive w/ airflow to keep the exhaust as quiet as possible. the restictivness of the exhaust is mostly contributed by "backpressure" . You get rid of your stock system and go w/ the right aftermarket setup and you gain power b/c youre exhaust is now free flowing and free of backpressure. You now have more torque at low and high end comapared to stock. But w/ the "theory" youre stating you have more torque w/ the stock system at low rpms b/c of backpressure...that is completely wrong...you have more w/ the aftermarket...like AcesHigh said the best exhaust would be no exhaust but thats not practical nor too environmental friendly. But you would have excellent top end and hardly any low end power. So you put correctly sized piping on your car and you have balanced it out to where you have more low end but less topend so youre creating torque through out the rpm range. This is not b/c you created backpressure when you put the system on there (unless it is undersized of course) its b/c it is now less free flowing. This adds torque at low end, i.e. the scavenging effect earlier mentioned, and lessens the torque at high end b/c it is not AS free flowing as it would be w/ no exhaust. Thats where the misconception of backpressure happens. Back pressure is not created when you put the system on just the outrageously free flowing effect of no exhaust is now reduced.

I will agree with Gohan Ryu; fast moving exhaust waves inherently create pressure. To eliminate any sort of pressure at all would be, in essence, to stop the exhaust pulses completely. Just like a fan that blows in your face creates pressure, if you turn this fan off, there would be none. If you have zero pressure in your exhaust, your engine would not be running. Take for example top end power. At high rpms, exhaust gases are moving so quickly that pressure/velocity is at its greatest. When you make the exhaust piping larger in this situation, the engine undoubtedly generates more power - there is no pressure to slow it down!

So you're saying low pressure and back pressure are the same thing? Don't think so. Backpressure is pressure that resists the motion of the normal movement. If you're talking about the low pressure pocket that a wave leaves in its wake, that's not the same thing. The internal combustion system operates on the principle that momentum of the exhaust pulses will keep the waves moving in the same direction.

Also, if you had zero pressure in your exhaust, a.k.a. a vacuum, you would actually create a massive amount of power for a few seconds until you blew up your engine.

But w/ the "theory" youre stating you have more torque w/ the stock system at low rpms b/c of backpressure...that is completely wrong.

This is where you are not understanding me. I'm not saying backpressure is the cause of stronger low-end torque. I don't know how to word this more plainly - forget everything that has been posted in this thread and consider the following statement....

"IF YOU TUNE YOUR EXHAUST TO HAVE ZERO BACKPRESSURE AT REDLINE YOU WILL INDUCE EXHAUST VELOCITY LOSS AT LOWER RPMS."

Zero backpressure at redline? The only way to do that would be NO exhaust, right?...or maybe using oversize piping?

But when you increase the size of the piping too much, you lose exhaust velocity; which is the reason for the "gutlessness" of your low end.

"Gutlessness" of your low end? Isn't that what I have been saying? Apparantly you agree with my "POINT" (not opinion, it's a fact - you said so yourself).

This is where you are not understanding me. I'm not saying backpressure is the cause of stronger low-end torque. I don't know how to word this more plainly - forget everything that has been posted in this thread and consider the following statement....

"IF YOU TUNE YOUR EXHAUST TO HAVE ZERO BACKPRESSURE AT REDLINE YOU WILL INDUCE EXHAUST VELOCITY LOSS AT LOWER RPMS."

Zero backpressure at redline? The only way to do that would be NO exhaust, right?...or maybe using oversize piping?



"Gutlessness" of your low end? Isn't that what I have been saying? Apparantly you agree with my "POINT" (not opinion, it's a fact - you said so yourself).

I never said I didnt agree w/ you that oversized piping causes gutlessness at lowend b/c of the reduced exhaust velocity. Where we disagree is you say the reason of low end torque is inducing exhaust velocity by creating backpressure at low rpms as you stated ina previous post:

"I agree with you that loss of exhaust velocity induces gutlessness on the low end. What I am saying is removing backpressure entirely causes loss of exhaust velocity (on the low end)."

and:

"Actually backpressure helps develop more torque on the low end...but you'll lose top end horsepower. With less backpressure you make more hp at higher revs, but it takes forever to get there because the low end has no torque."

Its not that backpressure helps develop more torque, torque is created b/c of the scavenging effect that starts at a lower rpm b/c of the reduced piping size.

You dont want to tune your exhaust at 9,000 rpm. You want to tune your exhaust for the rpm range that creates the most power. This is usually between 3500 and 6500 rpms for honda engines. If you do this you will have 0 backpressure at low rpms yet still have the scavenging effect b/c the exhaust pulses are moving at a speed high enough to create a lowpressure pocket in the wake of an exhaust pulse which will act as a vacuum and pull the next pulse along w/ it.

Its not that backpressure helps develop more torque, torque is created b/c of the scavenging effect that starts at a lower rpm b/c of the reduced piping size.

This is where you misunderstand me - because I said this:

"Actually backpressure helps develop more torque on the low end".
What I was implying:
1. Proper exhaust velocity makes more torque.
2. To have proper exhaust velocity on the low end, there HAS to be backpressure in the top end (6000rpm, 9000rpm - I don't care what you consider to be top end).

I'm sure I've made clear what I was implying in my subsequent posts - you just focused on that one line and ignored everything else I have said.

This is where you misunderstand me - because I said this:

.
What I was implying:
1. Proper exhaust velocity makes more torque.
2. To have proper exhaust velocity on the low end, there HAS to be backpressure in the top end (6000rpm, 9000rpm - I don't care what you consider to be top end).

I'm sure I've made clear what I was implying in my subsequent posts - you just focused on that one line and ignored everything else I have said.

1. I agree
2. I don't agree

I'll settle w/ knowing we agree on something and be done w/ it.

1. I agree
2. I don't agree

I'll settle w/ knowing we agree on something and be done w/ it.

Now that it's over with...what happened to the dork that posted something about his parents supercharged tractor? :icon16: j/k

Now that it's over with...what happened to the dork that posted something about his parents supercharged tractor? :icon16: j/k

Hey, I'm sorry I don't live on the internet like you do! Sitting back and watching you ladies duke it out was far more enjoyable anyway.

By the way, it's turbocharged.

Hey, I'm sorry I don't live on the internet like you do! Sitting back and watching you ladies duke it out was far more enjoyable anyway.

By the way, it's turbocharged.
Just kidding dude - that's what j/k stands for. Why did you delete the post?

Don't live on the internet? You sure responded to my post in a hurry! j/k again - don't get 'em in a bunch! Don't worry - we're all just passing free time until the work day is done (I'm getting $26 per hour while I do this).

I'm getting out of this thread before I get it closed.

So you're saying low pressure and back pressure are the same thing? Don't think so. Backpressure is pressure that resists the motion of the normal movement. If you're talking about the low pressure pocket that a wave leaves in its wake, that's not the same thing. The internal combustion system operates on the principle that momentum of the exhaust pulses will keep the waves moving in the same direction.

Also, if you had zero pressure in your exhaust, a.k.a. a vacuum, you would actually create a massive amount of power for a few seconds until you blew up your engine.

I just brought this back from the dead ~ things like this intrigue me.

Anyhow, the main problem I see with your model is this: you are assuming that a piston driven internal combustion engine relies solely on intake/exhaust pulses to operate. This simply is not true. While the intake charge does provide it with fuel and oxygen and the exhaust charge is driven out in close pattern, these things are not what power the pulses. It is the piston itself, after having finishing its stroke and driving out the waste products, that drives the cycle. As air expands and pushes the piston down, the force of this is driving the other three pistons.

Low pressure and backpressure are more or less synonymous with each other; you can't have low pressure and high backpressure (as in the case of a large diameter exhaust). Nor can you have high pressure and no backpressure (as in the case of a high revving motor... even with a large diameter exhaust, the pressure/backpressure increases with however many RPMs you go).

Now back to your vacuum model, you are assuming that there would be such a pressure drop between the exhaust manifold and the cylinder chamber that burnt mixture would be sucked out so quickly and efficiently that it would somehow (?) burn the motor out. Unfortunately, this kind of gradient is different from the one found in a turbocharger. We are dealing with negative atmosphere here; and (especially if the vacuum was found in the exhaust) no power would be made. There would be no air to start combustion.

I don't know about you, but the intake and exhaust ports in my engine don't open at the exact same time...

Hmmm, that makes me wonder...do sound waves travel in zero atmosphere? In outer-space no one could hear my fart can.