Do Bends Effect Power.. [Archive] - Yamaha R6 Forum: YZF-R6 Forums

: Do Bends Effect Power..


Wolf
09-24-2003, 04:49 AM
Penfold has asked that I answer this question, so I apologise in advance for the long techie post that will follow.

So do bends in exhaust pipes effect power? The short answer is yes , if they are done badly but NO, if tehy are done well.

The problem with bending steel is it tends to reduce in radius where it's bent and this will undoubtedly effect power adversly as the pipe radius effect gas volume in the pipe. In simple terms it is a restriction so slows gas flow. However, if like Wolf and most other top makers you only mandrel bend steel it does not compress at a bend. A set of balls, liek a pearl necklace is dropped down the tube as it's bent stopping the pipe from crushing . No crushing means no restriction. No restriction means the gas will flow as easily as it would in striaght pipe.

Try this test at home. Take a hose pipe and turn on the tap a set amount - say one turn. Time it a few seconds with the pipe dead straight and see how much water ends up in a measuring jug. Then gently loop the pipe, even in a complete circle and do the same again. If you are accurate you will ene dup with exactly the same amount of water each time. Exhaust gas is just the same...

The more important factors are pipe length and volume (obviously related) - if you use too narrow or too big a tube diameter you get losses in power and if you make the pipes too long or too short you get losses.

What may be confusing some people is that when they make a high pipe they loose power and they put this down to the bends - in reality unless they have crappy bends it may be due to the pipe now being longer and being the wrong length.

Gas moves in waves and there are certain optimum tuned lengths that suit the pulses of those waves and can set up positive reversion waves - other lengths may set up negative waves and actually (in very basic and simplified terms) push gas back in to the cylinder oosing power.

If you design a high pipe or an under seat pipe right, and bend with a ball mandrel, and get teh right pipe length it will work very well. No one has ever for example made a better performing system for teh Triumph T5 than our under seat system - it adds around 12 bhp compared to the next best system giving 8 bhp gain. And of course the new CBR1000 and R1 both have under seat pipes and both claim more power than teh previous models. Finally of course Ducati have won every Superbike championship for a decade with under seat pipes - no power problems there!

The key for people wanting a high pipe or an under seat is to ensure you buy it from someone who has designed it to work right rather than just made point a on a pipe meet point b and hope that it works...

stoneloco808
09-24-2003, 09:38 AM
very insightful.........

penfold
09-24-2003, 12:07 PM
Thanks Peter! That was great! Thanks for your time in explaining it simply enough where even I could understand it! :bow

It's always nice to be enlightened by someone in the know! YEA!

penfold
09-24-2003, 10:09 PM
I think this is something we should all think about when it comes time to consider a new exhaust, whether it is a standard mount, high mount, or underseats.

adhem_t
04-03-2004, 11:56 AM
This is precisely why i will be buying my new high mount exhaust form WOLF, HES THE MAN!!!! :bow :bow :bow :bow

loki1313
04-03-2004, 02:21 PM
good explanation wolf, i couldnt have put it any better myself. :cheers

Wolf
04-03-2004, 02:35 PM
thanks - shame my typos are so glaring when I just re-read it

off to practice my keyboard skills :mrgreen:

cowbomb02
07-13-2005, 10:27 AM
thx for the good info :screwy

imbobdole
12-24-2005, 12:40 AM
I can't help but partially disagree with the above statement, although it is a little old. First off, I'm relatively new to motorcycles but not even close to new with engines. The analogy to the hose shooting out water isn't the best for a couple reasons:
1-If you really want to use water as a comparison, then time it from when you turn the hose on with it empty until your jug is full with both, you'll notice that it in fact does take longer for the water to reach the end of the hose. The fact is, when you have the hose on full blast with a constant pressure, a constant amount of water will be exiting regardless; water cannot expand nor compress such as gases can. Once the pressure is established it will flow out of the hose at a constant rate as long as the loops in the pipe do not effect the diameter of it, so that much is correct. The fact is, with an exhaust system you do not have a constant flow; you have individual cylinders firing, meaning that, despite that they're firing VERY rapidly and may seem like it's a constant flow, it is not. Not to mention that gases do not flow like liquids anyway. Water and exhaust flow are like comparing apples and oranges.

2-Even when bends do not affect pipe radius, they still CAN cause a performance issue, albeit a small one in this case. But since we're talking technical terms, they do affect the performance. With a completely straight pipe, the exhaust is being shot out and, in a perfect world, is not hitting anything at all. (Read:no restrictions) The fact of the matter is that when you have a bend in the pipe, it is hitting the wall at an oblique angle. When the exhaust hits that wall, it causes a restriction, and herego a detraction from overall performance.

All in all, the short answer actually is YES. The bends can case a detraction in performance, although it may actually be a small one. I'm not just blowing smoke here; I'm a Physics major. I personally have performed experiments similar to this and found results accordingly. Sorry for the lengthy response, but I can't think of another way to say it in lesser words. Happy holidays to everyone

Agent4573
02-06-2006, 01:31 PM
2-Even when bends do not affect pipe radius, they still CAN cause a performance issue, albeit a small one in this case. But since we're talking technical terms, they do affect the performance. With a completely straight pipe, the exhaust is being shot out and, in a perfect world, is not hitting anything at all. (Read:no restrictions) The fact of the matter is that when you have a bend in the pipe, it is hitting the wall at an oblique angle. When the exhaust hits that wall, it causes a restriction, and herego a detraction from overall performance.

All in all, the short answer actually is YES. The bends can case a detraction in performance, although it may actually be a small one. I'm not just blowing smoke here; I'm a Physics major. I personally have performed experiments similar to this and found results accordingly. Sorry for the lengthy response, but I can't think of another way to say it in lesser words. Happy holidays to everyone

It's called head loss. Yes it effects the flow by increasing the pressure in the system needed to push the exhaust out at a certain speed, but because of the relatively low reynolds number of your exhaust gas flow, mandral bent tubing probably won't effect power output to a noticable amount. So your both right.

imbobdole
02-06-2006, 02:01 PM
It's called head loss. Yes it effects the flow by increasing the pressure in the system needed to push the exhaust out at a certain speed, but because of the relatively low reynolds number of your exhaust gas flow, mandral bent tubing probably won't effect power output to a noticable amount. So your both right.
and I thought III brought it back from the dead..
the topic wasn't how much it affects it, it was whether it affects it at all.. and it does.

donnys04r6
06-07-2007, 08:20 PM
I can't help but partially disagree with the above statement, although it is a little old. First off, I'm relatively new to motorcycles but not even close to new with engines. The analogy to the hose shooting out water isn't the best for a couple reasons:
1-If you really want to use water as a comparison, then time it from when you turn the hose on with it empty until your jug is full with both, you'll notice that it in fact does take longer for the water to reach the end of the hose. The fact is, when you have the hose on full blast with a constant pressure, a constant amount of water will be exiting regardless; water cannot expand nor compress such as gases can. Once the pressure is established it will flow out of the hose at a constant rate as long as the loops in the pipe do not effect the diameter of it, so that much is correct. The fact is, with an exhaust system you do not have a constant flow; you have individual cylinders firing, meaning that, despite that they're firing VERY rapidly and may seem like it's a constant flow, it is not. Not to mention that gases do not flow like liquids anyway. Water and exhaust flow are like comparing apples and oranges.

2-Even when bends do not affect pipe radius, they still CAN cause a performance issue, albeit a small one in this case. But since we're talking technical terms, they do affect the performance. With a completely straight pipe, the exhaust is being shot out and, in a perfect world, is not hitting anything at all. (Read:no restrictions) The fact of the matter is that when you have a bend in the pipe, it is hitting the wall at an oblique angle. When the exhaust hits that wall, it causes a restriction, and herego a detraction from overall performance.

All in all, the short answer actually is YES. The bends can case a detraction in performance, although it may actually be a small one. I'm not just blowing smoke here; I'm a Physics major. I personally have performed experiments similar to this and found results accordingly. Sorry for the lengthy response, but I can't think of another way to say it in lesser words. Happy holidays to everyone
+1
My buddy is an auto mechanic and the hose is def a bad example. Exhaust flows in a spiral, bends are bad because it disturbs the the flow, but it really doesnt make a huge difference.

b.burton
06-07-2007, 08:43 PM
I can't help but partially disagree with the above statement.....

I work with Nuclear steam generators & have a very good understanding of how gases/vapours flow and am 100% in agreement with bobdole.

We put bends/radius in steam piping to slow down flow.

But I think you would probably have a hard time measuring the power loss in a straight pipe vs. a pipe with bends, provided they are of the same length and volume, assuming no ovality occures during the bending process.

Birdman
04-07-2008, 02:13 AM
anyone wanna explain on another exhaust tpoic of flow etc regarding taper in the pipework? I'd think that would have more effect on performance than bends done correctly???

RedRiverRider
04-21-2008, 06:59 PM
I heard the less bends the better,( according to street tunner, hot rod mags.

JtGT29
05-22-2008, 01:20 PM
I heard that if you mix your fuel with lighter fluid and worcestershire sauce and bend your pipes conversly to x=y*x^Z/c+EMc^2 that you will gain maximum bhp or cause the universe to implode, i forget which one though.

ceo012384
05-22-2008, 02:16 PM
Try this test at home. Take a hose pipe and turn on the tap a set amount - say one turn. Time it a few seconds with the pipe dead straight and see how much water ends up in a measuring jug. Then gently loop the pipe, even in a complete circle and do the same again. If you are accurate you will ene dup with exactly the same amount of water each time. Exhaust gas is just the same...
Wait so a highly compressible gas is the same as a liquid, which is incompressible?

You need to take a basic fluid mechanics course.

Stoliguy
05-24-2008, 09:54 PM
We all ride Yamaha's, right?

Anyone care to do a history lesson on what got this company started?

The TUNING FORKS have a lot to do with Saxophones, and Saxophones share a bit in common with exhaust. That horn ain't straight.

My point? Bends can be good... Its not all about getting rid of the most all at once... its about tuning, and not just for sound... Yammie does this on purpose, guys.. great power at peak does NOT equal good racing. SMOOTH power does, and bends can help that (if done right). Physics of fluid/gas/sound movement do not explain this alone. This needs to be coupled with the characteristics of your motor (which can be changed with INTAKE, another bendy pipe.)

No Black/White answer here, I'm afraid... it's a bike by bike thing depending on your choices of what you change.

Ragz07
07-08-2008, 09:53 PM
it is a simple answer as long as the bends radius does not change.

Flynspeed
09-04-2008, 07:35 PM
IMBOBDOLE...excellent, simple answer using the laws of physics

Flynspeed
09-04-2008, 07:44 PM
IMBOBDOLE...excellent, simple answer using the laws of physics

Strictly Attitude
07-09-2009, 11:04 PM
can we through the use of back pressure in there?

Legit0168
07-10-2009, 11:49 AM
That's why Mandrel Benders were invented.

fuzzybuzzer
07-10-2009, 12:50 PM
thanks to everyone for your input and for the tech speak. I actually appreciate tech speak because most of my :BS (BS) is in Mechanical Engineering. It warms my heart to know that there are others who are not afraid of big words on an R6 somewhere.:toocool:

drgonzo
07-23-2009, 11:31 AM
All I can say is that you get what you pay for. Many of the better designed exhaust systems will be mandrel or pie cut (if titanium) and give the maximum radius.

SyZyGy
12-05-2009, 05:41 PM
I also had to chime in on this (even tho its semi-OT), mainly because there are people who are on a quest for power and believe that gutting their catalytic converter will create increases.

Do yourself a favor and do not gut the cat. Doing this will cause a little cavity in your exhaust, which will cause the high pressure gasses to decrease pressure as they enter that hollowed out cavity and then have to increase pressure again as it leaves that cavity. This whole "action" slows down the exhaust flow and will HURT power.:fact

If you want to get rid of the cat, get a pipe that will replace the segment of pipe that the cat is in. Doing this still MAY cause power loss, but no where near as much as just gutting the cat because in both scenarios you are still changing the TUNED exhaust's characteristics. I won't get into this much, as I am not a master of thermodynamics...

collins
02-25-2010, 03:20 PM
This Thread Is From 2005!!!!

SyZyGy
02-25-2010, 03:36 PM
This Thread Is From 2005!!!!

And yet you posted in it.....:sing










And its actually from 2003...

kena
07-05-2011, 10:58 PM
Try this test at home. Take a hose pipe and turn on the tap a set amount - say one turn. Time it a few seconds with the pipe dead straight and see how much water ends up in a measuring jug. Then gently loop the pipe, even in a complete circle and do the same again. If you are accurate you will ene dup with exactly the same amount of water each time. Exhaust gas is just the same... 2-Even when bends do not affect pipe radius, they still CAN cause a performance issue, albeit a small one in this case. But since we're talking technical terms, they do affect the performance. With a completely straight pipe, the exhaust is being shot out and, in a perfect world, is not hitting anything at all. (Read:no restrictions) The fact of the matter is that when you have a bend in the pipe, it is hitting the wall at an oblique angle. When the exhaust hits that wall, it causes a restriction, and herego a detraction from overall performance.

Panici
07-05-2011, 11:13 PM
SPAM

I see what you did there...

http://captionsearch.com/pix/thumb/pijobf4e8h-t.jpg