Back pressure questions

CR250 Rider I will try to answer the questions in order. As far as revving the engine with the mufflers off it does not cause damage. The engine does not care. Having a less restricted air intake and exhaust WILL give you better performance but the cost is higher gas consumption. You will not see top fuel dragsters mufflers. Some engine noise does come from the intake system. You can get slip on mufflers. It is easier and that way you do not have to take apart your stock muffler system. although you would learn a lot about HONDA mufflers. I have a 4 into 2 system myself. There is no reason usually to alter the header tubes. The balancing chamber could be done away with if necessary. There are different ways to abate noise from the exhaust. You will see many methods. Fiberglass packing,Perforations, tubes made of screens with holes and so forth and each one produces a different result. On jet engines the exhaust portion of the engines have a wavy surface to cut down on the noise. Basically you have straight exhaust tubes that are the same size as the header tubes. Like early model sportsters with drag pipes. Those have to have baffles that are perforated tubes of different lengths and different designs. Then you have mufflers that are larger diameter that the header tubes to try to relieve pressure but then have a baffle included to reduce the sound. You will see mega phones and reverse cone megaphones . Roll up a news paper like funnel and speak through it. See how much louder it is? But the revers cone megaphone tries to return part of that pressure wave to slow that air down a bit. That is where some of the dynamics of having pulse waves hitting the exhaust port right at the time of overlap when some intake gasses are escaping through the exhaust and returning the wave in time to stop that unburnt fuel. A shorty muffler would probably give you the right back pressure and good deep sound you would like. Google "shorty slip on muffler" The only thing that CAN cause damage is if you have NO exhaust tubes at all on the engine and it is very cold outside and the valves are very hot. There could be warpage but It is like getting lock jaw from a rusty nail. Have you ever heard od anyone getting lock jaw? Have you ever seen actual damage from an engine that had no exhaust tubes? A long time ago motorcycles had engines that just had header tubes a few inches in length. How much back pressure and where that back pressure occurs at different rpms can be used to make the engine perform a certain way for different purposes. Having a smooth power curve is important too. Not just having it all at once. And all that exhaust stuff is the same for intake tract length too, in combo with the exhaust. But manufactures need to consider how it sounds too. If they make a good looking muffler that sounds "right" then why would anyone want to change it? I can think of some bikes and cars that no one changed the exhausts because they were "right". Power is not every thing except in drag racing.

Sorry for some misspelling.I am in a hurry right now to leave.

 

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:tea::tea:

 

Apology accepted Don, and yes... smileys, emoticons, hell I'd have even taken an LOL for Christs sake! :frown:

I put a lot of time into writing the post in question because I felt it was relevant to what everyone seems to want to do to their bikes as soon as they get them. New wheels and new exhaust. It gives it that customized look and sound to set them apart from the rest. Unfortunately, most of the guys I talk to about it are very uneducated in regards to the function of the exhaust pipes and don't realize that even a simple slip on can radically reduce the performance of the engine if it's not designed for that type of engine.

I guess because I took some time preparing and posting it, your comments kinda pissed me off (especially the jab on my not doing my own work since I got crap on here while doing my carbs and apparently I'm still a bit touchy about it :tongue. Next time please don't forget to note your sarcasm. Not all of us can hear your fingers giggling when you press the send key.

*And to all those who've said thanks... you're welcome. If you've got any other Q's you'd like me to address, please PM me and I'll dig some useful info up your way.

Long-winded In AZ, out! :smile:

 

Respectfully I think this may be bit of false advertising.

At WOT you will gain (some) HP but a motorcycle is not a dragster - i.e. at low and mid-range an unrestricted pipe will negatively affect performance.

 

Thought american women were different from italians, but evidently I was wrong!