Please explain exhaust theory to me

[The Stranger:Me]

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"....

[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:Me]

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:Me]

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.

[MSTRS:Me]

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. Norman Einstein's Imp Theory is perhaps not as widely known as it should be and I blame....lessee, hmmm, LABOUR and HULUN CLARK

[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...

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