Please explain exhaust theory to me

[Colapop]

Ok, so you get a new bike. One of the things people talk about doing to improve it's performance is to change the exhaust - Akrapovic, Two Brothers, Yoshimura... etc. That's great. A new exhaust looks good, sounds good and makes your wallet lighter. But what does it actually do? What difference does an exhaust pipe make? If it's about 'breathing' better (apart from the sound law) wouldn't it be better to leave the exhaust pipe off? Is there a reason for the length of exhaust pipe? Anyone care to give me a reason for varying types of exhausts?

[nodrog]

have a read here, you are pretty brainy so it should answer some of your questions.

http://www.burnsstainless.com/TechArticles/Theory/theory.html

[vifferman]

Oh nodrog - what a party pooper you are.
If only you hadn't posted that link, you would've left room for the KB X-spurts to post all kinds of interesting, convoluted and misinformed bollocks about zorsts. :crybaby:

[NighthawkNZ]

Please explain exhaust theory to me

Petrol goes in the tank comes out the exhaust... :lol:

[nodrog]

Oh nodrog - what a party pooper you are.
If only you hadn't posted that link, you would've left room for the KB X-spurts to post all kinds of interesting, convoluted and misinformed bollocks about zorsts. :crybaby:

im doing my best to save server space, go planet!

[Morcs]

Looks faster and sounds faster - therefore - makes bike faster.

[Winston001]

have a read here, you are pretty brainy so it should answer some of your questions.

http://www.burnsstainless.com/TechArticles/Theory/theory.html

Take no notice of that site, its all Intelligent Design type stuff.

The truth is, when you put petrol in your tank, very small imps take it and deposit tiny bucketloads in a magic furnace. This is called an " Impulse". The furnace is there to keep the dragon happy and its task in life is to try and fly out of the cavern it is trapped in.

The dragon pushes against the front of the cavern and attacks it with gusto (another magical element made from oil). This force is transmitted through the engine which is just a fancy cover for the cavern, to the frame of your bike, and pushes the bike forward. The rear wheel follows giving the illusion that it is doing the work.

The exhaust is nothing more than a fancy chimney for the furnace. However dragons are noisy creatures and have been known to escape so the exhaust is designed to make this as difficult as possible.

Straight pipes are great for the furnace but sometimes dragons can get through them and the motorcycle stops. This incidentally is why you see Harley Davidsons stopped quite often.......

[Pwalo]

It keeps the after market exhaust makers in business.

[koba]

While having a natter this morning a mate and I also noted that a fancy super exhaust on a sportsbike is much better value for money than the titanium fancy one he can get for his turbo sports car.

We thought this because the bikes 'zorst represents a far greater proportion of the bikes total mass and with an engine tuned for top end power like a sportsbike is probably going to make far greater use of removing noise and gas emmision limiters.

We also noted the main reason that a sportsbike owner seems (to us at least) more likley to shell out big $$ for an exhaust is you can SEE it (and the brand on the side of it) alot better than on a sports car, although it may give performance gain that really doesn't mean shit all in real world road riding.

[MSTRS]

I have noticed in recent years that manufacturers have started to grab hold of quantum technology and put it (in the form of Black Holes) into their exhausts.
This, of course, means that fuck all escapes in the form of detectable gas and sound emissions.
It is every biker's task to ensure that this emasculating modern technology is resisted at any cost. To which end, we need to be grateful that there are still manufacturing types out there who recognise that not all that is new is good. Fail to support these wonderful philostines at your (and my)...oh, and his...peril.

[The Stranger]

Looks faster and sounds faster - therefore - makes bike faster.

Everybody knows that more niose = more power.

[nodrog]

Everybody knows that more niose = more power.

not always

http://www.kiwibiker.co.nz/forums/picture.php?albumid=599&pictureid=7746

[AllanB]

The most interesting recent change in after-market mufflers for bikes is the db killer insert - designed to shut the muffler up to legal levels. What is interesting about this is that most of the major makers also claim that the db killer will not reduce the performance of their muffler (when bolted onto a stock bike).

I also notice that 95% of these mufflers have the db killer removed. This leads to the conclusion that a aftermarket muffler is all about noise.

(an estimate for you wankers who will demand documented proof of my posted %)

More noise - and bloody rightly so :2thumbsup

Now there will be some who will state that the weight difference between a stock (heavy) and slip-on muffler (light) gives a performance gain - this is in theory very true however I doubt you can actually notice it unless you are on the track being timed to the 100th second. And I conclude if this weight loss was so important to them then why do they not go on a diet and lose 20kg - this would make the greatest performance gain to their bike.

In addition to all this HONDAS RULE. Period.

[AllanB]

not always

http://www.kiwibiker.co.nz/forums/picture.php?albumid=599&pictureid=7746


Now that's not true - everyone knows that a 1600cc Harley with open pipes will go from 67 to 69 hp.
:girlfight::dodge::dodge::dodge:

[The Stranger]

Ok, enough of the bullshit.

First mod to the Fazer was a PC only, that yeilded +4.5hp peak with gains in the top half of the rev range only.
Next was an air filter and Yoshi can (this removed one cat) that yeilded +9hp peak but healthy gains from 4k up.

The XT is a whopping 41hp std and with pipe and air filter only was pulling 45hp. Gains were only available in the top half of the rev range.
With the PC we have gains through the entire rev range, and surprisingly quite an increase in fuel economy to go with it - despite tipping a lot of additional fuel, go figure.

All measurements are on the same dyno.

Draw your own conclusions.

[The Stranger]

The most interesting recent change in after-market mufflers for bikes is the db killer insert - designed to shut the muffler up to legal levels. What is interesting about this is that most of the major makers also claim that the db killer will not reduce the performance of their muffler (when bolted onto a stock bike).

I also notice that 95% of these mufflers have the db killer removed. This leads to the conclusion that a aftermarket muffler is all about noise.



If I run the Fazer with the db killer in it robs any gains made by all of the other mods.

[slofox]

Take no notice of that site, its all Intelligent Design type stuff.

The truth is, when you put petrol in your tank, very small imps take it and deposit tiny bucketloads in a magic furnace. This is called an " Impulse". The furnace is there to keep the dragon happy and its task in life is to try and fly out of the cavern it is trapped in.

The dragon pushes against the front of the cavern and attacks it with gusto (another magical element made from oil). This force is transmitted through the engine which is just a fancy cover for the cavern, to the frame of your bike, and pushes the bike forward. The rear wheel follows giving the illusion that it is doing the work.

The exhaust is nothing more than a fancy chimney for the furnace. However dragons are noisy creatures and have been known to escape so the exhaust is designed to make this as difficult as possible.

Straight pipes are great for the furnace but sometimes dragons can get through them and the motorcycle stops. This incidentally is why you see Harley Davidsons stopped quite often.......

Best explanation I have EVER seen, Winston001.....!!!! Makes a damn sight more sense than my book "Scientific design of intake and exhaust systems"....:rofl:

[forkoil]

Ok, enough of the bullshit.

First mod to the Fazer was a PC only, that yeilded +4.5hp peak with gains in the top half of the rev range only.
Next was an air filter and Yoshi can (this removed one cat) that yeilded +9hp peak but healthy gains from 4k up.

The XT is a whopping 41hp std and with pipe and air filter only was pulling 45hp. Gains were only available in the top half of the rev range.
With the PC we have gains through the entire rev range, and surprisingly quite an increase in fuel economy to go with it - despite tipping a lot of additional fuel, go figure.

All measurements are on the same dyno.

Draw your own conclusions.
So you are basically saying the most improvement was the opposite for the two bikes? This is no doubt a function of the relative efficiency of the original component(s) to the aftermarket "improvements". Model knowledge helps eh. Thats was what was great about the old RD days, cos there was so many around, it was easy to find out what gave best bang for the $, though these days the internet makes that easier.

[The Stranger]

So you are basically saying the most improvement was the opposite for the two bikes? This is no doubt a function of the relative efficiency of the original component(s) to the aftermarket "improvements". Model knowledge helps eh. Thats was what was great about the old RD days, cos there was so many around, it was easy to find out what gave best bang for the $, though these days the internet makes that easier.

I'm not so sure that I would say opposite, however 100% with you on the efficiency of the original components.
The Fazer is known to be weak in the low-mid range. After market headers make huge gains in this area.
The air supply restrictive on both bikes, but more so on the XT.

[Colapop]

Will someone with fairly standard abilities notice much if any difference? Commuting for example will still be commuting but with more noise. The differentiation between exhausts is principally for the track or riding fast? I've been looking at diifferent bikes and been told often by various people "That'll be so much better with a **** can" If I buy a bike that has 100hp and fit an exhaust that gives it +5hp what difference will it make in the real world to the way the bike runs? Will it be more fuel efficient, less fuel efficient, run smoother, handle better, make coffee? I'm beginning to think that aftermarket exhausts are much like wings fitted to the back of boy racer cars - only any good at speeds that the vehicle (or operator) can't handle anyway...

[AllanB]

Will someone with fairly standard abilities notice much if any difference? Commuting for example will still be commuting but with more noise. The differentiation between exhausts is principally for the track or riding fast? I've been looking at diifferent bikes and been told often by various people "That'll be so much better with a **** can" If I buy a bike that has 100hp and fit an exhaust that gives it +5hp what difference will it make in the real world to the way the bike runs? Will it be more fuel efficient, less fuel efficient, run smoother, handle better, make coffee? I'm beginning to think that aftermarket exhausts are much like wings fitted to the back of boy racer cars - only any good at speeds that the vehicle (or operator) can't handle anyway...


Well it will sound louder and more aggressive and you will thus ride it more aggressively thus go faster!!!!!!!

I made a minor mod to the outlets of my stock Hornet mufflers (no bucks for after-market cans) and replaced the 25mm stock outlet with 35mm ones - the note is not very loud but a lot deeper. The most obvious change I noticed (other than a bit louder and a lot deeper) is that the bike is even smoother through the entire rev range.

Plus those wings on the boy-racer cars do do something - they stuff up a perfectly good boot!

[The Stranger]

Will someone with fairly standard abilities notice much if any difference? Commuting for example will still be commuting but with more noise.

Not a lot of difference to commuting, however depending on the bike it may make it more ridable and pull cleaner from low throttle settings.


The differentiation between exhausts is principally for the track or riding fast? I've been looking at diifferent bikes and been told often by various people "That'll be so much better with a **** can" If I buy a bike that has 100hp and fit an exhaust that gives it +5hp what difference will it make in the real world to the way the bike runs?

You will notice say 5hp difference to your own scoot. Not sure what your angle is here. Do you want more power or not? If not don't do it, simple.

Will it be more fuel efficient, less fuel efficient, run smoother, handle better, make coffee?

Potentially the exhaust will make small changes to fuel efficiency, but I wouldn't bank on it.

I'm beginning to think that aftermarket exhausts are much like wings fitted to the back of boy racer cars - only any good at speeds that the vehicle (or operator) can't handle anyway...

Perhaps - but as part of a package of changes the exhaust is contributing to 18% additional power from the XT in the mid range (used every ride) and is getting over 10% better fuel economy. If you read my previous post then drew that comparrison to the boy racer wing I am sorry for you, there really is little I can do to help your understanding.

The Fazer has +5hp at 3,500rpm and +20hp at 7,000rpm so definately in a range usable by mere mortals. Economy is about the same as it was before making any changes. Yes you REALLY do feel it and the engine is much smoother running at low RPM.


:2thumbsup

[MSTRS]

The Fazer has +5hp at 3,500rpm and +20hp at 7,000rpm so definately in a range usable by mere mortals. Economy is about the same as it was before making any changes. Yes you REALLY do feel it and the engine is much smoother running at low RPM.
There ya go, Col. It's not a waste of time. PLUS, the after market cans generally look way nicer than the honking great chunks of tubing on many bikes. Especially the new ones.

[Winston001]

I can't believe so many people are sucked into all of this "engineering" belief system. Really - as if some mysterious being would construct a piece of metal like a motorcycle and hang a great cumbersome, tortuous pipe on the side of it...... <_<

No no no. :no: Norman Einstein's Imp Theory is perhaps not as widely known as it should be and I blame....lessee, hmmm, LABOUR and HULUN CLARK :2guns:

[icekiwi]

. A new exhaust looks good, sounds good and makes your wallet lighter.

Lighter wallet=lighter rider=faster bike....

[Marmoot]

Petrol goes in the tank comes out the exhaust... :lol:

So if you make your exhaust so small you can save some petrol

Or block completely.
True story...

[portokiwi]

So what is realy wrong with the factory pipes???

[Colapop]

Will someone with fairly standard abilities notice much if any difference? Commuting for example will still be commuting but with more noise.

Not a lot of difference to commuting, however depending on the bike it may make it more ridable and pull cleaner from low throttle settings.


The differentiation between exhausts is principally for the track or riding fast? I've been looking at diifferent bikes and been told often by various people "That'll be so much better with a **** can" If I buy a bike that has 100hp and fit an exhaust that gives it +5hp what difference will it make in the real world to the way the bike runs?

You will notice say 5hp difference to your own scoot. Not sure what your angle is here. Do you want more power or not? If not don't do it, simple.

Will it be more fuel efficient, less fuel efficient, run smoother, handle better, make coffee?

Potentially the exhaust will make small changes to fuel efficiency, but I wouldn't bank on it.

I'm beginning to think that aftermarket exhausts are much like wings fitted to the back of boy racer cars - only any good at speeds that the vehicle (or operator) can't handle anyway...

Perhaps - but as part of a package of changes the exhaust is contributing to 18% additional power from the XT in the mid range (used every ride) and is getting over 10% better fuel economy. If you read my previous post then drew that comparrison to the boy racer wing I am sorry for you, there really is little I can do to help your understanding.

The Fazer has +5hp at 3,500rpm and +20hp at 7,000rpm so definately in a range usable by mere mortals. Economy is about the same as it was before making any changes. Yes you REALLY do feel it and the engine is much smoother running at low RPM.
Thank you!! That's really what I wanted to know.

a) I will notice it.
b) New cans do have a quantifiable effect on the bike.
c) They will look good!

[Gremlin]

So what is realy wrong with the factory pipes???
new bike has cats in it, hottest pipes I have ever come across, boiling to the touch, makes them a bit dangerous too. Aftermarkets will run cooler (less of them, and better materials).

When I bought the zx10, it came with its stock and an akrapovic titanium one fitted. Took the akrapovic off, it still weighed a hefty amount, and weighed less than the stock. Fitted a racefit growler, at 825 grams it was bloody light.

Instantly noticed the change in balance when riding it down the road, not to mention the performance gains and (of course) the sound.

Its also another way of personalising your ride.

[The Pastor]

they also reduce alot of weight, making u faster

[portokiwi]

Thanks for that

[stormy1]

What can i say. As long as they dont rob power i'm all for an exhaust syetm that makes a bike sound like a bike! Just love the sound of the two brothers cans on my VTR! Sound good, look good = makes me feel good, no more needs to be said!

[FROSTY]

Short version.
Factory pipes have to do their bit to help the bike perform as well as keep its noise town to a level accepted by whatever countrys gubiment the bike is sposed to be sold at. AND has to pass the emmission laws of said gubiment.
Aftermarket pipes in NZ dont have those worries.

What it means to you is that within reason you can buy a louder pipe cos it sounds good.
You can buy a pipe which has tuned size/width to suit better bottom end,midrange or top end.

Thats the simple version.

[wharfy]

have a read here, you are pretty brainy so it should answer some of your questions.

http://www.burnsstainless.com/TechArticles/Theory/theory.html

Pretty good read...

All that good stuff is directly related to the intake side as well - You have to consider the entire FUEL system from airbox,intake,carb/injector,inlet-tract,inlet-port(s),combustion chamber,exhaust port(s) and everything after that.

Modern bikes have to consider emissions, noise, economy, as well as performance in the market the bike is intended for.
Change any of the components of the entire fuel system and you will compromise some of the others.

BUT knowing ALL that I still removed my bikes vacuum operated intake flap (noise control for the rev range measured for compliance) fitted a K&N filter and removed a bit of the exhaust baffle with NO evidence that it has altered the performance/economy/emissions (for better or worse) but it does SOUND much cooler now :) (and still gets a warrant)