do i need back presure?

[alwazjeepin69]

on my 99 zx6 do i need back pressure from the exshast? lmk thanks

[Nickels]

Ima guess yes. At least some. Usually its turbod motors that dont need back pressure. Im not 100% sure about bikes, but im guessing same rules apply.

[jaceface]

yes, i have found that a potato will give you the most back pressure....

[triumph955i]

I took of my exhaust once to see how loud it was and it seemed slower. Didnt have the same get up and go that it normally does in low rpm. So yes a certain of back pressure is good.

[95gsx]

more back pressure, more stable and steady of low end. and on a carbed bike i rode with just a mid pipe and it rode fine. little slow on reaction time... not sure but i think without back pressure you might hurt the valves

[01F4izzy]

more back pressure, more stable and steady of low end. and on a carbed bike i rode with just a mid pipe and it rode fine. little slow on reaction time... not sure but i think without back pressure you might hurt the valves

we dont even know if that bike was carbed. lol

[jaceface]

yes its good to have, and yes its bad to have. you have to find the middle ground.....

[95gsx]

more back pressure, more stable and steady of low end. and on a carbed bike i rode with just a mid pipe and it rode fine. little slow on reaction time... not sure but i think without back pressure you might hurt the valves

we dont even know if that bike was carbed. lol


stupid kawis i swear to god it was FI with a bar choke for higher RPMs to stunt.... probably explained why there was a sprocket. silly me for not knowing anything back then.

[01F4izzy]

it couldnt have been to stunt either because they all have them.

[95gsx]

does ryans bike have that? i think a 02 swap with choke controls would be a sensible mod

[01F4izzy]

does ryans bike have that? i think a 02 swap with choke controls would be a sensible mod

no but the 03-04s are way different than 05+ and that orange one at cooks had it and there is no way its that big of a coincidence that two 03-04s from cooks had an 02 swap done to them

[95gsx]

true maybe a kawi owner could fill this one in.

[jaceface]

are you talking about the little lever on the clip-on that makes the bike bike idle faster?

[Burntz]

You have probably heard words like: back pressure, scavenging, tuned length, merged collector, rotational firing order, compatible combination and many others that meant something, but how they relate to a header may be a little vague. This article should give you a basic understanding of how a header works, what the terminology means, and how it plays a part in the header's performance gains.

The first misconception that needs to be cleared up is that a header relieves backpressure, but a certain amount of backpressure is needed for optimum performance. Just the opposite is true. A good header not only relieves the backpressure, but goes one step further and creates a vacuum in the system. When the next cylinder's exhaust valve opens, the vacuum in the system pulls the exhaust out of the cylinder. This is what the term "Scavenging" means.

The first consideration is the proper tube diameter. Many people think "Bigger is Better", but this is not the case. The smallest diameter that will flow enough air to handle the engine's c.c. at your desired Red Line R.P.M. should be used. This small diameter will generate the velocity (air speed) needed to "Scavenge" at low R.P.M.s. If too small a diameter is used the engine will pull hard at low R.P.M.s but at some point in the higher R.P.M.s the tube will not be able to flow as much air as the engine is pumping out, and the engine will "sign off" early, not reaching its potential peak R.P.M. This situation would require going one size larger in tube diameter.

The second consideration is the proper tube length. The length directly controls the power band in the R.P.M. range. Longer tube lengths pull the torque down to a lower R.P.M. range. Shorter tubes move the power band up into a higher R.P.M. range. Engines that Red Line at 10,000 R.P.M. would need short tube lengths about 26" long. Engines that are torquers and Red Line at 5,500 R.P.M.s would need a tube length of 36". This is what is meant by the term "Tuned Length". The tube length is tuned to make the engine operate at a desired R.P.M. range.

The third consideration is the collector outlet diameter and extension length. This is where major differences occur between four cylinder engines and V-8 engines. The optimum situation is the four cylinder because of it's firing cycle. Every 180 degree of crankshaft rotation there is one exhaust pulse entering the collector. This is ideal timing because, as one pulse exits the collector, the next exhaust valve is opening and the vacuum created in the system pulls the exhaust from the cylinder. In this ideal 180 degree cycling the collector outlet diameter only needs to be 20% larger than the primary tube diameter. (Example: 1 3/4" primary tubes need a 2" collector outlet diameter.) The rule of thumb here is two tube sizes. This keeps the velocity fast to increase scavenging, especially at lower R.P.M.s. Going to a larger outlet diameter will hurt the midrange and low R.P.M. torque.

The amount of straight in the collector extension can move the engines torque up or down in the R.P.M. range. Longer extension length will pull the torque down into the midrange.

Engines that "Red Line" at 10,000 R.P.M. would only need 2" of straight between the collector and the megaphone. This is just enough length to straighten out the air flow before it enters the megaphone. This creates an orifice action that enhances exhaust velocity.

In the case of V-8 firing order, the five pulses fire alternately back and forth from left to right collector, giving the ideal 180 degree firing cycle. Then it fires two in succession into the left collector, then two in succession into the right collector. If the proper collector outlet diameter is being used (two sizes larger than primaries) the two pulses in succession load up the collector with more air than it can flow. This results in a very strong midrange torque, but causes the engine to "sign off" early, not reaching its potential peek R.P.M. The improper firing order on a V-8 engine results in the need to use large diameter collectors so the engine will perform well at high R.P.M.s. Unfortunately the large diameter collectors cause a tremendous drop in air velocity, resulting in less scavenging through the entire R.P.M. range.

Often cams are used with extended valve timing to help the exhaust cycling. This results in valve timing overlap (Intake and Exhaust valves both open at T.D.C.) which causes a "Reversion"cycle in the exhaust. When this happens, exhaust actually backs up into the cylinder causing intake air to be pushed back out the intake. This reversion causes "Standoff" (fuel blowing out of the Intake) at low R.P.M.s. This whole improper cycling has resulted in a number of "Cure Alls" to help stop this reversion and standoff.

The plentum intake was created to stop the fuel "Standoff". Then came "Anti Reversionary" Cones in the exhaust tubes, and stepped tube diameter in the header, extended collector lengths and even plentums in the exhaust tubes.

In this chain of events beginning with improper firing order, a series of cures has developed, each one causing a new problem.

The optimum cure to this whole problem is to correct the exhaust firing cycle. The two cylinders that fire in succession into each collector have to be separated. This can be done partially by a "Tri-Y" header, where the four primary tubes from each bank merge into two secondary tubes (separating the two pulses firing in succession) and finally collect into a single collector. This type of header helps, but the two pulses are still coming back together at the collector.

The second optimum cure is to cross the two center tubes from each bank, across the engine running them into the collector on the opposite side. This makes the firing cycle in each collector 180 degrees apart, the same as a four cylinder engine. Once this firing order is achieved, the small collector outlet diameter can be used and the "High Velocity Scavenging" at low R.P.M.s cures the reversion problems and eliminates the need for extreme cam duration.

This sounds so easy, you are probably asking why wasn't this done from the start?

If you have ever seen a set of 180 degree headers you would understand.

On today's cars, with space virtually nonexistent, crossing four tubes either under the oil pan or around the front or rear of the engine presents major problems. On racing applications where it is possible, there is still the problem of keeping the tube length down to a reasonable 32" long. If that's not enough challenge, then try to arrange the tubes into each collector so they fire in a "Rotational Firing" pattern. Then you have, what has been called "A Bundle of Snakes".

Arranging the tubes to fire rotationally adds to the scavenging capabilities. The exhaust gas exiting one tube, passing across the opening of the tube directly beside it, creates more suction on that tube than it would on a tube on the opposite side of the collector.

The next problem is "Turbulence" in the collector. When four round tubes are grouped together in a square pattern, so a collector can be attached, you notice a gapping hole in the center of the four tubes. The standard method in manufacturing headers is to cap this hole off with a square plate. This plate in the center of the four tubes creates dead air space, or turbulence, disrupting the high velocity in the collector. This problem is solved by using a "Merge Collector". This collector is formed from four tubes, cut at approximately an 8 degree angle on two sides. When the tubes are all fitted together they form a collector with a "Pyramid" in the center. This has eliminated the need for the square plate and has taken up some of the volume inside the collector, speeding up the air velocity.

Other methods of curing this problem are: fabricating a pyramid out of sheet metal and welding it over the hole between the tubes, or squaring the tubes on two sides so they fit together forming a "+" weld in the center eliminating the hole all together.

You can see that there are a great many factors that go into making a good header. When the header, intake system, and cam timing are all designed to operate to their maximum in the same R.P.M. range, then you have a "Compatible Combination". This combination can be tuned to deliver maximum power at any desired R.P.M. range.

These are some of the "Basics" you need to know about building a good high performance header. There are many other adjustments that can be made to fine tune a header, but this should give you a basic understanding of how all the components work together.

[95gsx]

are you talking about the little lever on the clip-on that makes the bike bike idle faster?

yes

[jaceface]

that lever is a fast idle lever, not a choke. (on the 03/04 kawis). they were manual fast idle on the kawis where as the honda was on fast idle automatically until it reached a certain temp. you were supposed to run that fast idle until the temp reached like 100 or something close to that then ride it.

[95gsx]

hmmm thats why mine ran crap unless it was on.

[turbodaytona87]

You have probably heard words like: back pressure, scavenging, tuned length, merged collector, rotational firing order, compatible combination and many others that meant something, but how they relate to a header may be a little vague. This article should give you a basic understanding of how a header works, what the terminology means, and how it plays a part in the header's performance gains.

The first misconception that needs to be cleared up is that a header relieves backpressure, but a certain amount of backpressure is needed for optimum performance. Just the opposite is true. A good header not only relieves the backpressure, but goes one step further and creates a vacuum in the system. When the next cylinder's exhaust valve opens, the vacuum in the system pulls the exhaust out of the cylinder. This is what the term "Scavenging" means.

The first consideration is the proper tube diameter. Many people think "Bigger is Better", but this is not the case. The smallest diameter that will flow enough air to handle the engine's c.c. at your desired Red Line R.P.M. should be used. This small diameter will generate the velocity (air speed) needed to "Scavenge" at low R.P.M.s. If too small a diameter is used the engine will pull hard at low R.P.M.s but at some point in the higher R.P.M.s the tube will not be able to flow as much air as the engine is pumping out, and the engine will "sign off" early, not reaching its potential peak R.P.M. This situation would require going one size larger in tube diameter.

The second consideration is the proper tube length. The length directly controls the power band in the R.P.M. range. Longer tube lengths pull the torque down to a lower R.P.M. range. Shorter tubes move the power band up into a higher R.P.M. range. Engines that Red Line at 10,000 R.P.M. would need short tube lengths about 26" long. Engines that are torquers and Red Line at 5,500 R.P.M.s would need a tube length of 36". This is what is meant by the term "Tuned Length". The tube length is tuned to make the engine operate at a desired R.P.M. range.

The third consideration is the collector outlet diameter and extension length. This is where major differences occur between four cylinder engines and V-8 engines. The optimum situation is the four cylinder because of it's firing cycle. Every 180 degree of crankshaft rotation there is one exhaust pulse entering the collector. This is ideal timing because, as one pulse exits the collector, the next exhaust valve is opening and the vacuum created in the system pulls the exhaust from the cylinder. In this ideal 180 degree cycling the collector outlet diameter only needs to be 20% larger than the primary tube diameter. (Example: 1 3/4" primary tubes need a 2" collector outlet diameter.) The rule of thumb here is two tube sizes. This keeps the velocity fast to increase scavenging, especially at lower R.P.M.s. Going to a larger outlet diameter will hurt the midrange and low R.P.M. torque.

The amount of straight in the collector extension can move the engines torque up or down in the R.P.M. range. Longer extension length will pull the torque down into the midrange.

Engines that "Red Line" at 10,000 R.P.M. would only need 2" of straight between the collector and the megaphone. This is just enough length to straighten out the air flow before it enters the megaphone. This creates an orifice action that enhances exhaust velocity.

In the case of V-8 firing order, the five pulses fire alternately back and forth from left to right collector, giving the ideal 180 degree firing cycle. Then it fires two in succession into the left collector, then two in succession into the right collector. If the proper collector outlet diameter is being used (two sizes larger than primaries) the two pulses in succession load up the collector with more air than it can flow. This results in a very strong midrange torque, but causes the engine to "sign off" early, not reaching its potential peek R.P.M. The improper firing order on a V-8 engine results in the need to use large diameter collectors so the engine will perform well at high R.P.M.s. Unfortunately the large diameter collectors cause a tremendous drop in air velocity, resulting in less scavenging through the entire R.P.M. range.

Often cams are used with extended valve timing to help the exhaust cycling. This results in valve timing overlap (Intake and Exhaust valves both open at T.D.C.) which causes a "Reversion"cycle in the exhaust. When this happens, exhaust actually backs up into the cylinder causing intake air to be pushed back out the intake. This reversion causes "Standoff" (fuel blowing out of the Intake) at low R.P.M.s. This whole improper cycling has resulted in a number of "Cure Alls" to help stop this reversion and standoff.

The plentum intake was created to stop the fuel "Standoff". Then came "Anti Reversionary" Cones in the exhaust tubes, and stepped tube diameter in the header, extended collector lengths and even plentums in the exhaust tubes.

In this chain of events beginning with improper firing order, a series of cures has developed, each one causing a new problem.

The optimum cure to this whole problem is to correct the exhaust firing cycle. The two cylinders that fire in succession into each collector have to be separated. This can be done partially by a "Tri-Y" header, where the four primary tubes from each bank merge into two secondary tubes (separating the two pulses firing in succession) and finally collect into a single collector. This type of header helps, but the two pulses are still coming back together at the collector.

The second optimum cure is to cross the two center tubes from each bank, across the engine running them into the collector on the opposite side. This makes the firing cycle in each collector 180 degrees apart, the same as a four cylinder engine. Once this firing order is achieved, the small collector outlet diameter can be used and the "High Velocity Scavenging" at low R.P.M.s cures the reversion problems and eliminates the need for extreme cam duration.

This sounds so easy, you are probably asking why wasn't this done from the start?

If you have ever seen a set of 180 degree headers you would understand.

On today's cars, with space virtually nonexistent, crossing four tubes either under the oil pan or around the front or rear of the engine presents major problems. On racing applications where it is possible, there is still the problem of keeping the tube length down to a reasonable 32" long. If that's not enough challenge, then try to arrange the tubes into each collector so they fire in a "Rotational Firing" pattern. Then you have, what has been called "A Bundle of Snakes".

Arranging the tubes to fire rotationally adds to the scavenging capabilities. The exhaust gas exiting one tube, passing across the opening of the tube directly beside it, creates more suction on that tube than it would on a tube on the opposite side of the collector.

The next problem is "Turbulence" in the collector. When four round tubes are grouped together in a square pattern, so a collector can be attached, you notice a gapping hole in the center of the four tubes. The standard method in manufacturing headers is to cap this hole off with a square plate. This plate in the center of the four tubes creates dead air space, or turbulence, disrupting the high velocity in the collector. This problem is solved by using a "Merge Collector". This collector is formed from four tubes, cut at approximately an 8 degree angle on two sides. When the tubes are all fitted together they form a collector with a "Pyramid" in the center. This has eliminated the need for the square plate and has taken up some of the volume inside the collector, speeding up the air velocity.

Other methods of curing this problem are: fabricating a pyramid out of sheet metal and welding it over the hole between the tubes, or squaring the tubes on two sides so they fit together forming a "+" weld in the center eliminating the hole all together.

You can see that there are a great many factors that go into making a good header. When the header, intake system, and cam timing are all designed to operate to their maximum in the same R.P.M. range, then you have a "Compatible Combination". This combination can be tuned to deliver maximum power at any desired R.P.M. range.

These are some of the "Basics" you need to know about building a good high performance header. There are many other adjustments that can be made to fine tune a header, but this should give you a basic understanding of how all the components work together.
Couldn't have said it better myself

cliffs: any back pressure is bad, but unfortunately its an unwanted side effect of scavenging.

[Jester]

there is no way im reading that.

[95gsx]

i'm guessing copy paste from another site.

[_TEX_929]

your still going to have some back pressure but you need to if it has fucked with air/fuel ratio if you have lean surges or if you are poping through your exasust on deceloration its not a good thing i just gutted the exaust on a 2006 zzr600 and havent had a problem accordint to fuji its the same bike so jsut need to know if you are having lean surges or if the exaust is popping on decel.

[B.A.D.]

i'm guessing copy paste from another site.
yeah, either that or Justin's IQ just tripled

[Burntz]

I know all about backpressure and all that shit, I just didn't feel like typing and the guy who wrote this article worded it oh so well lol

[B.A.D.]

haha, just givin ya shit man...

You DO need some backpressure, I lowered mine with the exhaust on my 650R and I have noticed some Popping on deceleration, but there should be no damage from that on my bike, because I have a "PAIR" valve, it let's excess fuel from the fuel system move to the catylitic converter to burn it off, since I eliminated the Cat from my exhaust setup, the excess fuel vapor goes out the exhaust, causing a light popping(and occasionally a flame if the engine is still cold 8-)

[Burntz]

I got that popping and crackeling shit on mine too, dam yoshi pipe haha

[Nickels]

^thats from teh motor being a suzuki motor. Notice none of the Hondas on teh dyno on sunday popped?

[95gsx]

except mo daddy's 919 that bitch shot flames.

[Nickels]

Thats different..

[Mr. Jeff]

and travis's 6rr

[Mr. Jeff]

and that yellow f4i

[Burntz]

pwnt lol. I just needa get a pc3 and tune it. Havn't had the moneys

[Nickels]

Fuck you all, i didnt watch the dynos, lol.

[95gsx]

fucking squid

[Mr. Jeff]

just about every bike that didnt have a cat on it popped

[Burntz]

Yea true, mine never had one from the get go tho

[Nickels]

Well i guess thats kinda common sense. Seeing how the excess gas doesnt get burned off in the cat.

[Mr. Jeff]

my bike doesnt pop

[05barbiestunter636]

Yeah jeff your right it EXPLODES in our ear drums!! lol You need at least something for alittle back pressure otherwise you gonna be losing power cause you run way to lean. If you look at mine its comeplety straight piped and i lost about 5 horsepower from it and it pops really bad

[95gsx]

any worrys about bending valves without enough back pressure or not?

[Burntz]

lol no you won't be bending a valve. Like I said guys, their is NO SUCH THING AS BACKPRESSURE.

Thats a word people made up. It has to do with how the air exits and how the vehicle is tuned, and how the timing is set.

If you were running straight exhaust ports with no exhaust whatsoever, you could actually warp a valve, but only if the motor was really hot and it was real cold outside. Cold air on really hot valve = not good.

[jaceface]

http://dictionary.reference.com/browse/backpressure

yes, there is such a thing. if you dont believe so i can physically prove to you that it does.

[Burntz]

ill rephrase that, theirs no such thing as "needing" backpressure. Im a dumbass of course their is such thing as backpressure lol.

[Nickels]

And there is a such thing as needing back pressure..

[Mr. Jeff]

And there is a such thing as needing back pressure..
true story, when i take my pipe off it runs like shit.

[jaceface]

thats because you lose gas velocity. backpressure is a byproduct of gas velocity.

[Nickels]

Justin, sometimes i would just stop while you are behind.

[Burntz]

And there is a such thing as needing back pressure..

Thats where you are wrong sir. You can never NEED backpressure. Hence why sprint cars run open headers, and turbo cars want minimal backpressure

Maybe you need a certain amount of backpressure based on your stock tune, but pull the pipe off and re-tune it, and I guess you don't need it.

Read this : http://www.uucmotorwerks.com/html_produ ... uemyth.htm (http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm)

[Nickels]

Why dont they run open heads then?

[06_636]

'they' do. It just depends on the application.

[Nickels]

They just run open heads? No exhaust piping what so ever?

[06_636]

yes alot of race cars run open headers.
The point of buying tuned headers is to run them open.
Certain applications and engines require back pressure to perform at their best.
Other applications will run better with less back pressure.
It all has to do with the application and the tuning.

[05barbiestunter636]

how come the only one that really sounds like they are making sense is jace? Just drop it. if i need to ill grab my teacher of motorcycle class and have him type in here and shut everyone up. I dont even know why you are talkin about race cars and sprint cars cause if you realize who started this post im sure hes not wondering if he needs back pressure for a sprint car application and im sure open headers is a great app for a vehicle that your replacing or goin through the engine every 2-5 races.

[Burntz]

Ok then well back to the original post

He doesn't even have that bike any more.

To run the best it possibly can, it needs the stock exhaust with the stock tune, or else his mixture will be off. Yes that bike requires a certain amount of backpressure for its stock fuel settings.

The open headers response etc was to nickels, who said everything that has a motor needs backpressure, which isn't always true. Its all about how you adjust fuel delivery and timing.

Ryan your bike would run excellent with the straight pipe you have now if you got a pcIII and tuned it. Which you should do, because you go to SCC and all and have access to the dyno lol

[jaceface]

so in your logic if i have 2 inch tubes coming off a small block into a large collector open to atmosphere i should be able to "tune it properly for that" WRONG!! if you dont have the GAS VELOCITY then it does no good. the problem is having gas velocity creates backpressure. you want the gas to be flowing through to continiously and as fast as possible. to big a pipe and it will move slow, to small a pipe and it wont be able to flow freely enough and you end up with more backpressure and less velocity.

[Nickels]

With the running open heads thing, im trying to get at, they have a little bit of back pressure from their headers, meaning that they do have some back pressure.
Personally, i would trust Jace over a college instructor.. Its a known fact that he has proven his teacher wrong before.

[06_636]

I re-read my last post and Im pretty sure that I didnt say that an engine would ever run well with NO back pressure, just that the amount of back pressure would depend on the application. Im not very educated on the matter so I believe Jace, I think I just worded it wrong...

[Nickels]

I was targeting my all my comments toward Justin.