Do Bends Effect Power.. - Yamaha R6 Forum: YZF-R6 Forums
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post #1 of 30 (permalink) Old 09-24-2003, 03:49 AM Thread Starter
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Do Bends Effect Power..

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...

Regards

Peter Sorrell
Wolf Racing
www.wolfracing.co.uk
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post #2 of 30 (permalink) Old 09-24-2003, 08:38 AM
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very insightful.........
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post #3 of 30 (permalink) Old 09-24-2003, 11:07 AM
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Thanks Peter! That was great! Thanks for your time in explaining it simply enough where even I could understand it!

It's always nice to be enlightened by someone in the know! YEA!
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post #4 of 30 (permalink) Old 09-24-2003, 09:09 PM
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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.
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post #5 of 30 (permalink) Old 04-03-2004, 10:56 AM
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This is precisely why i will be buying my new high mount exhaust form WOLF, HES THE MAN!!!!

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post #6 of 30 (permalink) Old 04-03-2004, 01:21 PM
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good explanation wolf, i couldnt have put it any better myself.

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post #7 of 30 (permalink) Old 04-03-2004, 01:35 PM Thread Starter
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thanks - shame my typos are so glaring when I just re-read it

off to practice my keyboard skills

Regards

Peter Sorrell
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post #8 of 30 (permalink) Old 07-13-2005, 09:27 AM
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thx for the good info

" it is wat it is "
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post #9 of 30 (permalink) Old 12-23-2005, 11:40 PM
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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
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post #10 of 30 (permalink) Old 02-06-2006, 12:31 PM
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Quote:
Originally Posted by imbobdole
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.

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