Changing exhausts

[Hero125]

Hi all

I've got a hero 125 and I'm wondering if I can put a new end can on or will i possibly lose power? 

 

[Joe85]

9 hours ago, Hero125 said:

Hi all

I've got a hero 125 and I'm wondering if I can put a new end can on or will i possibly lose power? 

 

I imagine strong gusts of wind will have more impact on your power than changing the end can.

[fastbob]

Who knows ? Buy a £30 can off Amazon and see what happens . 

[bud]

The engine needs a certain amount of back pressure. So something with a baffle in will definitely work better than a straight through pipe.

I wouldn't expect any performance gain from it though.

when my mate fitted a noisy pipe to his CBF125 he lost 5mph off the top speed.

[onesea]

5 hours ago, bud said:

The engine needs a certain amount of back pressure. So something with a baffle in will definitely work better than a straight through pipe.

I wouldn't expect any performance gain from it though.

when my mate fitted a noisy pipe to his CBF125 he lost 5mph off the top speed.

My nephew fitted a larger boar exhaust to his 125cc.

He reckons he got no more on his top speed, however he thinks he got a little more torque (hence speed) up hill...

 

Your not going to make any significant increases in an power or speed IMHO.

 

Ask yourself what your trying to achieve.

[Joe85]

On 01/08/2022 at 00:20, bud said:

The engine needs a certain amount of back pressure. So something with a baffle in will definitely work better than a straight through pipe.

I wouldn't expect any performance gain from it though.

when my mate fitted a noisy pipe to his CBF125 he lost 5mph off the top speed.

Is this actually true? Does an engine really need exhaust back pressure? For what purpose? 

[Stu]

38 minutes ago, Joe85 said:

Is this actually true? Does an engine really need exhaust back pressure? For what purpose? 

 

No! 

 

But you get more mid range power with it 

[billy sugger]

When I learnt about gas flow it was taught to me that a certain amount of back pressure helps to improve the flow of aireated fuel into the cylinders and the removal of exhaust gases afterwards. Its something to do with vortexes, and how they affect the movement of air/gases in a enclosed environment. I worked as a Air conditioning unit builder for a few years, and had to travel to a massive IBM facility near Portsmouth (Havant) to help fix a flaw in the sub-contractors installation of the units I built. They used the wrong sized ducting to spread the cooled air throughout the facility, so the air just wasn't moving. It was cheaper to modify the AC units than to change the ducting, so I spent three weeks atop a cherry picker, ( bloody high up as well) changing fans and their surrounds to create back pressure and get the system working properly. 

On the same track, I have a 250 that has a balancer pipe joining two equal length exhaust pipes on a twin cylinder engine, and due to its position it gets covered in crud and rusts badly, so I tried two unconnected exhausts and the bike would not run properly, especially at low revs, so had to revert back to a linked system. A twin with equal length pipes should not need a balance tube unless there is a issue with the exhaust gases expulsion from the cylinders

[fastbob]

8 hours ago, Joe85 said:

Is this actually true? Does an engine really need exhaust back pressure? For what purpose? 

It pains me to say this but I'm sure that the grizzled old sage himself would have an answer . 

Edited August 4, 2022 by fastbob

[MikeHorton]

1 hour ago, fastbob said:

It pains me to say this but I'm sure that the grizzled old sage himself would have an answer . 

Is there a picture of Kevin going to make it into next year's tmbf calender? 

[billy sugger]

All 12 pages I reckon

[Mississippi Bullfrog]

When I flew competition model aircraft engines were tuned with back pressure, the exhaust system was a tuned pipe.

 

They were two strokes of course where back pressure certainly was a thing to bear in mind.

 

When I had a VanVan people used to fit aftermarket exhausts with less back pressure and they found two things, a loss of power and higher oil consumption. 

[billy sugger]

Engine builders used to believe the partial vacuum from a piston returning to BDC was enough to draw the fuel mixture in, but its way more complicated than that. Even the inlet/outlet ports shape can have an effect on the flow, fluid dynamics is worth researching when it comes to uprating your engine, as I learnt in the early eighties working on my 125 single

[Stu]

22 hours ago, billy sugger said:

When I learnt about gas flow it was taught to me that a certain amount of back pressure helps to improve the flow of aireated fuel into the cylinders and the removal of exhaust gases afterwards. Its something to do with vortexes, and how they affect the movement of air/gases in a enclosed environment. I worked as a Air conditioning unit builder for a few years, and had to travel to a massive IBM facility near Portsmouth (Havant) to help fix a flaw in the sub-contractors installation of the units I built. They used the wrong sized ducting to spread the cooled air throughout the facility, so the air just wasn't moving. It was cheaper to modify the AC units than to change the ducting, so I spent three weeks atop a cherry picker, ( bloody high up as well) changing fans and their surrounds to create back pressure and get the system working properly. 

On the same track, I have a 250 that has a balancer pipe joining two equal length exhaust pipes on a twin cylinder engine, and due to its position it gets covered in crud and rusts badly, so I tried two unconnected exhausts and the bike would not run properly, especially at low revs, so had to revert back to a linked system. A twin with equal length pipes should not need a balance tube unless there is a issue with the exhaust gases expulsion from the cylinders

 

This explains it well 

 

While and engine doesn't NEED back pressure it helps and different levels of back pressure affect how power is achieved across the rev range 

 

More back pressure = more mid range and less top end power 

 

Less back pressure = less mid range but more top end power 

 

it is a fine art though 

[Bender]

https://www-rideapart-com.cdn.ampproject.org/v/s/www.rideapart.com/features/353186/ask-rideapart-exhaust-back-pressure/amp/?amp_gsa=1&amp_js_v=a9&usqp=mq331AQKKAFQArABIIACAw%3D%3D#amp_tf=From %1%24s&aoh=16596512690649&referrer=https%3A%2F%2Fwww.google.com&ampshare=https%3A%2F%2Fwww.rideapart.com%2Ffeatures%2F353186%2Fask-rideapart-exhaust-back-pressure%2F

[bud]

On 04/08/2022 at 10:52, Mississippi Bullfrog said:

When I flew competition model aircraft engines were tuned with back pressure, the exhaust system was a tuned pipe.

 

They were two strokes of course where back pressure certainly was a thing to bear in mind.

 

When I had a VanVan people used to fit aftermarket exhausts with less back pressure and they found two things, a loss of power and higher oil consumption. 

Oh no. A double fail!

[bud]

On 03/08/2022 at 22:17, Joe85 said:

Is this actually true? Does an engine really need exhaust back pressure? For what purpose? 

He even sold the exhaust to his mate who had the same bike. With the same result.