My question is...Can this be used on an all motor set up? If placed further back?

 

bzzzump! im thinkin right after the cat it should work? so theres still some back pressure? anyone else done it with a modest na set up?

 

bump... interested in this too...

 

 

Just wanna add.... ya... it can be used after the cat in an all motor setup.... I just want to know how well it works...lol

 

haha me too

 

are we talkin about the exhaust cut outs like a good old fashioned header dump except electrical and not cable operated? i ran one of those for like 6 months during track season until the little flapper stopped shutting. i had it where the cat would normally go. man!! those were the good ole days. nuthin like hearin v-tec with no exhaust. especially when you accelerate hard next to someone that thinks he's kewl......then pull the cable right before vtec is about to go.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JICsube &raquo;</TD></TR><TR><TD CLASS="quote">bzzzump! im thinkin right after the cat it should work? so theres still some back pressure? anyone else done it with a modest na set up?</TD></TR></TABLE>

Back pressure is always bad.

 

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

Back pressure is always bad.</TD></TR></TABLE>

C'mon !!! That's just not true ! At low rpm it would help with exhaust scavenging... basic header design meng !

 

That has everything to do with exhaust velocity, and nothing to do with having backpressure.

Backpressure = always bad

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StyleTEG &raquo;</TD></TR><TR><TD CLASS="quote">That has everything to do with exhaust velocity, and nothing to do with having backpressure.
</TD></TR></TABLE>

I know it has to do with exhaust velocity...what do you think controls the velocity of the exhaust pulses in the lower half of the piping and the collector ? With no restriction whatsoever... low rpm scavenging will be affected.

No disrespect intended, but your blanket statement about 'backpressure' is wrong.

 

It is not wrong.

A smaller pipe allows the pulses to move faster at low RPM's, and the trailing end of the pulse creates a vaccum. This vaccum pulls the other pulses out, quicker, and the exiting pulses pull in fresh intake charge durring overlap.

That is exhaust velocity.

What happens when you throw a clogged cat into the mix? Well now you have a ton of backpressure, so low RPM scavanging should be increased by your reasoning correct? But it won't, it will just slow everything down because the exhaust can't travel fast enough to create a vaccum. It will just hit the bottleneck and build pressure.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StyleTEG &raquo;</TD></TR><TR><TD CLASS="quote">It is not wrong.

A smaller pipe allows the pulses to move faster at low RPM's, and the trailing end of the pulse creates a vaccum. This vaccum pulls the other pulses out, quicker, and the exiting pulses pull in fresh intake charge durring overlap.

That is exhaust velocity.</TD></TR></TABLE>

First off... it's not 'vaccum'... it's an area of low pressure.

Secondly... yes, your overall statement is correct, but what you failed to mention is this:
1) As rpm increases, the scavenging effect decreases...
2) As you decrease the 'back pressure' by increasing pipe diameter (or open header) after the primaries on a header, you begin to equalize exhaust pressure more quickly... this will decrease the amount of low pressure available at the rear end of the exhaust pulse (closer to the port) which not only will decrease scavenging, but also slow the velocity of the following pulse due to the absence of the intense low pressure which was previously present (particularly noticable at low rpm.)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StyleTeg &raquo;</TD></TR><TR><TD CLASS="quote">
What happens when you throw a clogged cat into the mix? Well now you have a ton of backpressure, so low RPM scavanging should be increased by your reasoning correct? But it won't, it will just slow everything down because the exhaust can't travel fast enough to create a vaccum. It will just hit the bottleneck and build pressure.</TD></TR></TABLE>

CLOGGED CAT ? Why do so many HT people ALWAYS quote an extreme situation ???

I NEVER said increasing back pressure means increased performance... NEVER even alluded to it... go double check there, pumpkin.

But if ya must use extreme situations.....kewl ! Here's one with your logic of how backpressure affects an engine:

If backpressure were ALWAYS bad as you say... then some 2" primaries would make a great n/a header !

 

Calm down, no need to get upset. This is just a discussion.

You are mixing two ideas and presenting them as one.

Backpressure is always bad.

A smaller tube is going to create a higher exhaust velocity at the sacrifice of quantity. Higher exhaust velocity in the low end, will increase low end scavanging. At higher end power is this going to create backpressure?

Yes, it will. Does that mean that backpressure is good for low end performance? No. It means higher exhaust velocity in the low rpms is good for low end performance.

Backpressure is a side effect, it is not the cause of better low end scavanging. Backpressure is always a bad side effect, you do not want backpressure. Sometimes having backpressure is a trade off, but saying that backpressure is good for low end power is not true.

The area of low pressure creates a vaccum. That is what I ment.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
Backpressure: The myth and why it's wrong.

I. Introduction

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

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StyleTEG &raquo;</TD></TR><TR><TD CLASS="quote">Calm down, no need to get upset. This is just a discussion.</TD></TR></TABLE>

HAHAH... buddy... I am calm.... if I weren't... you'd really know. Takes alot to irk me... I just like to debate.

I don't need basic reading on this issue... you'll notice I normally say 'backpressure' in quotes for a reason.

Basically what I'm saying is that the blanket statement is not accurate... The original topic of the cutout will slow exhaust velocity for a large portion of the rpm band, but I'm not going to bother to elaborate any further.

 

Eh, your responses seem hostile, even your last one.

Back-pressure by itself is always bad. You don't want resistance to flow in the exhaust system. When you are getting that low end scavenging that you were discussing, how much back-pressure is in the system at that time?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StyleTEG &raquo;</TD></TR><TR><TD CLASS="quote">Eh, your responses seem hostile, even your last one.

Back-pressure by itself is always bad. You don't want resistance to flow in the exhaust system. When you are getting that low end scavenging that you were discussing, how much back-pressure is in the system at that time?</TD></TR></TABLE>

Trust me... It wasn't meant to be hostile... I was on my way to lunch and didn't feel like continuing. You are trying to make it look like I'm flaming you or something... what's up with that ?

As far as how much backpressure when the scavenging is occuring... dude... seriously... stop being so closed minded. An engine is a air pump... you cannot isolate one event and ask why some actions are not taking place at that time... which is exactly what you are doing in the question you just posed. Unless you were trying to be sarcastic....

X2 (No, you're not special... I'm not mad or angry at you.... take a valium... smoke a philly...get a massage...w/e you wanna do... life is great... you drive a honda and X2's not mad at you. )

 

I was just explaining my reasoning for saying calm down.

I am not being close minded, one could argue that you are being just as close minded as I (if I was).

My point was that I see what you are trying to say. That a smaller exhaust pipe will increase low end scavanging and exhaust velocity, at the expense of backpressure in the high RPMS. However, backpressure is not the cause of the low end scavanging and higher exhaust velocity. So by saying that sometimes backpressure is good, is misleading. Because in reality you never want backpressure. Sometimes its just a side effect you have to deal with.

When the low end scavanging occurs, there is very little backpressure. Its just when the engine creates more exhaust, that the pressure builds up.