[ddnuts]

What does it mean when the exhaust pipes are bigger? I was at out local Italian bike shop and there was a 999r with extensive work done to it. The salesman told me to look at the size of the pipe leading to the cans vs. the stock size. There was a huge difference between the two. I was wondering what are the benefits of have larger pipes if any. If there is why isn't the pipes for the RG3 bigger than the stock ones? Can anyone educate me on the matter. Thanks in advance.

 

[luvtolean]

Theoretically it offers less restriction in flow, allowing you to make more HP.

But bigger is not always better. You can put too big a pipe on a bike, and make less power, especially less "area under the curve" power.

 

[ARCHILLE]

According to the thermo-dynamic theory, exhaust flow needs some back pressure (ie.,scavenging effect).

 

[airfuel]

Like luvtolean states, the bigger pipes are used to get more peak hp and mostly used on tracks where you can keep the engine singing full blast.

The downside is usually a loss of hp/tq down low where most of us off the track run.
As my father said many times, "there is no free lunch"

John

 

[luvtolean]

According to the thermo-dynamic theory, exhaust flow needs some back pressure (ie.,scavenging effect).

Here we go again.

Back pressure is never, ever a good thing in an exhaust system.

But adding bigger pipes will not necessarily reduce backpressure. Wave propagation, timing, cam events and several other factors all effect this.

Here's an interesting report from CAFE and the FAA on aircraft exhaust system tuning. The "Background" section specifically addresses backpressure as always being a negative thing. (they even mention bikes)

http://www.cafefoundation.org/aprs/epg.pdf

Ideally, what you really want is below ambient pressure (sometimes called "suction", but there is no such thing, only a lack of pressure) in the exhaust header when the exhaust valve opens. This will help better scavenge the combustion chamber and depending on your overlap in the cam, might even help pull the intake charge down.

Bigger pipes work better with higher exhaust flows. At low flows the pipes don't have a high enough exhaust energy to keep the gas moving down the (big) tube, and backpressure results at low RPM, hurting efficiency, tq and ultimately HP.

 

[ARCHILLE]

Here we go again.

Back pressure is never, ever a good thing in an exhaust system.

But adding bigger pipes will not necessarily reduce backpressure. Wave propagation, timing, cam events and several other factors all effect this.

Here's an interesting report from CAFE and the FAA on aircraft exhaust system tuning. The "Background" section specifically addresses backpressure as always being a negative thing. (they even mention bikes)

http://www.cafefoundation.org/aprs/epg.pdf

Ideally, what you really want is below ambient pressure (sometimes called "suction", but there is no such thing, only a lack of pressure) in the exhaust header when the exhaust valve opens. This will help better scavenge the combustion chamber and depending on your overlap in the cam, might even help pull the intake charge down.

Bigger pipes work better with higher exhaust flows. At low flows the pipes don't have a high enough exhaust energy to keep the gas moving down the (big) tube, and backpressure results at low RPM, hurting efficiency, tq and ultimately HP.

Nicely put, luv!

ddnuts, bigger is not always better. I have to admit that the Leo Vinci 57/60 system mid piple is almost twice the OEM one.

 

[luvtolean]

Here's my favorite spot to start for exhaust tech BTW. This is where that aircraft report is from.

http://www.burnsstainless.com/TechArticles/techarticles.html

When I win the lottery, these guys will be building Inconel exhaust systems for all my performance toys. (until I get good enough with TIG and engine modeling to do it myself!)

 

[airfuel]

Great info and tech reading.

Glad we have some smart people on this forum. This cold get good! (and very technical) :nerd: :nerd: :nerd:

John

 

[ddnuts]

Thanks guys for that info, very helpful and insightful. You guys are collectively awesome. I'm sure I'll have more questions in the future, so get ready.

Here is another that just popped up. Why is that contraption that holds breasts in place called a Bra (singular)? While that undergarment which is next to the best thing on earth, is called Panties (plural)?

What is a panty or bras?

Thanks for the help?

 

[luvtolean]

I'm most interested in the parts that reside under those garments...and don't care much what they're called as long as they're laying on the floor.

 

[airfuel]

Agreed! ling-er-yee is great for about 20 seconds, then it gets in the way! :naughty:

(way off topic, sorry)

 

[ARCHILLE]

ddnuts,

How do you like the BSTs you got from Eric?

 

[ddnuts]

ARCHILLE, sorry for taking so long to get back to you. The wheels are awesome. Right away I was able to notice a difference. The front comes up in the first 3 gears no problem. We have some track time coming up soon. How have you been? I haven't heard from you since the days of MVF4.com. Are you going over for MotoGP this summer?

 

[odonata]

I'm most interested in the parts that reside under those garments...and don't care much what they're called as long as they're laying on the floor.

In this case, bigger is better, and back pressure is always a good thing :laughing:

 

[john]

In this case, bigger is better, and back pressure is always a good thing :laughing:

Funny, that's what my wife says too. :laughing: :laughing: :naughty: :naughty:

 

[alvin]

Funny, that's what my wife says too. :laughing: :laughing: :naughty: :naughty:

:laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing:

 

[odonata]

:laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing::laughing:

Are we hijacking this thread? oh, wait, the topic is "Exhaust pipe diameter???" I guess it is still relevant.


:laughing: