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Discussion Starter #1
I've been thinking about redoing my exhaust on the 2 gen, I am planning on leaving the stock header alone, might keep stock cat in place too, but after that thinking about going with dual exhaust, and have an exhaust valve on one pipe, so basically it's going to flow all the exhaust through one pipe and at around 5k rpm the secondary exhaust pipe will open up. Haven't done proper research just yet, they might both be the same size ( dual 1 5/8 pipes should be able to support 185hp and single 1 5/8 should be good for around 92hp or roughly 7k rpm), I am wanting to keep the exhaust quiet for daily riding and having a higher flow muffler for the secondary pipe. Basically it'll sound stock till I go over certain rpm and then it'll open up and get louder.

Any ideas? anybody ever done something like this on bikes? I know I've seen something similar on bmw cars at one point. I still have to get the pros and cons on this set up, weight is obviously will be con.
 

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Honestly it's probably gonna be more hassle than it's worth. BMW isn't the only company to do that Aston Martin still does but they do it for 2 reasons. 1 keeps sound levels more civil while around town and 2 because of the increased back pressure helps create more tq at lower revs. But again it's kind of pointless because the exhaust sevro already does this. Now if your refering to a dump switch you'd have no gain in power.
 

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Discussion Starter #3
Honestly it's probably gonna be more hassle than it's worth. BMW isn't the only company to do that Aston Martin still does but they do it for 2 reasons. 1 keeps sound levels more civil while around town and 2 because of the increased back pressure helps create more tq at lower revs. But again it's kind of pointless because the exhaust sevro already does this. Now if your refering to a dump switch you'd have no gain in power.
I want to do it for 3 reasons, noise levels ( quiet just riding around and loud when in higher rpms), fuel efficiency, more bottom end torque.

Btw, back pressure never helps anything, bottom end torque is due to velocity. I keep hearing back pressure this and back pressure that :crackup:, back pressure is always bad.
 

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It already has a exhaust valve so I dont think adding another one will help with torque. And if back pressure is bad than take the bike to a dyno with open headers vs. with good cans and let us know what happens.
 

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If you want it done properly get an akrapovic race system you don't need the evo, but considering you want it to be more fuel efficient getthe evo and save more weight. Tune it so it's more fuel efficient than stock and leave the baffle in in the end cap. I say akrapovic too because there pretty quite open for what they are and they scream too but not like a wild hooker.
 

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Discussion Starter #6
It already has a exhaust valve so I dont think adding another one will help with torque. And if back pressure is bad than take the bike to a dyno with open headers vs. with good cans and let us know what happens.
I am taking the stock one out and replacing it with another one that would go on one side of the exhaust only. I dont know about you but my bike has only one header lol.
 

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It already has a exhaust valve so I dont think adding another one will help with torque. And if back pressure is bad than take the bike to a dyno with open headers vs. with good cans and let us know what happens.
:+1:

Your Exactly right all engines need back pressure. Some people have a mis conception about the idea prob cause they see large displacement v8s running open headers. The reason is the headers actually make enough backpressure to keep it happy. This is not the case on our bikes, they need the headers and a muffler.
 

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they need back pressure to keep exhaust gases around long enough to keep the exhaust valve cool and from burning up.

....open the flow and lessen the back pressure, flow increases, more fuel is required cause now the motor doesn't push as hard to get the exhaust out, becoming more efficient and needing said fuel to keep valves alive.

Along the header and pathway of 4-2-1-2, or what ever combo, the exhaust pulses compliment each other to create efficiency to make a system better then another system.

running 2-3 foot exhaust systems make great power, but are loud as hell (duh)....So when making exhaust systems there is alot of options.
The motor is an air pump, the quicker and least restricted way to get rid of the spent gases the more efficient it will be.
 

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Discussion Starter #9
:+1:

Your Exactly right all engines need back pressure. Some people have a mis conception about the idea prob cause they see large displacement v8s running open headers. The reason is the headers actually make enough backpressure to keep it happy. This is not the case on our bikes, they need the headers and a muffler.
Oh I got it, our bikes need the headers and a muffler, my bike only came with a header and 2 mufflers, so I should put another header on there and take the muffler out so I would have headers and a muffler

Thanks buddy.
 

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Discussion Starter #10
they need back pressure to keep exhaust gases around long enough to keep the exhaust valve cool and from burning up.

....open the flow and lessen the back pressure, flow increases, more fuel is required cause now the motor doesn't push as hard to get the exhaust out, becoming more efficient and needing said fuel to keep valves alive.

Along the header and pathway of 4-2-1-2, or what ever combo, the exhaust pulses compliment each other to create efficiency to make a system better then another system.

running 2-3 foot exhaust systems make great power, but are loud as hell (duh)....So when making exhaust systems there is alot of options.
The motor is an air pump, the quicker and least restricted way to get rid of the spent gases the more efficient it will be.
I am confused by this post first you say they need back pressure to keep hot exhaust gasses to keep the valve cool? wouldn't it make it hot, cause exhaust gases are hot? Then you say it needs to be less restricted? And how do the exhaust pulses compliment each other to create efficiency?
 

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It already has a exhaust valve so I dont think adding another one will help with torque. And if back pressure is bad than take the bike to a dyno with open headers vs. with good cans and let us know what happens.
I don't think he's looking for torque, he's just trying to limit the noise. If you tap into the rpm signal, you could rig up some sort of exhaust servo (possibly using the stock unit if you could figure out how to control it) -- it won't be easy, but it's possible.

With proper tuning, an open exhaust will always make more power than a muffled system. A muffler reduces the decibel level by either restricting airflow, absorbing sound waves, or expanding the exhaust gases so that they slow down and reflect internally -- any way you look at it, you are taking energy out of the system and/or causing a restriction (backpressure), both of which will reduce power. The only way an open system wouldn't outperform a muffled system is if you dump it at the collector and the header collector was not designed to be run open (that is, the system requires an additional length of pipe before terminating for ideal operation).


they need back pressure to keep exhaust gases around long enough to keep the exhaust valve cool and from burning up.

The motor is an air pump, the quicker and least restricted way to get rid of the spent gases the more efficient it will be.
I agree with your second point completely, but I disagree with your first. The exhaust gases are incredibly hot -- the valves do not get cooled by keeping those gases around, but rather are cooled by the incoming cool air/fuel charge and the transfer of heat to the head (and consequently oil and coolant).

Ever hear the old adage about burning up your valves if you don't run a header? It's not because the flow speeds up to the point that the fuel mixture then becomes lean, it's because the backpressure becomes so high that the burnt gases can't properly escape and the combustion temps climb to ridiculously high levels. The header is there to direct gases away from the port as quickly and efficiently as possible -- dumping right into the atmosphere from the head is a disaster from a fluid dynamics perspective.
 

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Oh I got it, our bikes need the headers and a muffler, my bike only came with a header and 2 mufflers, so I should put another header on there and take the muffler out so I would have headers and a muffler

Thanks buddy.
Dude your a smart ass. You know what i was saying. But please Go be a retard with whatever you want To do. I could careless I Was just trying to give you a tip. Sorry I chimed in. If u wanna make less power go ahead dumbass.
 

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A perfect burn is 14.7:1..........running a safe 12.8:1 at WOT under high load has alot of "cooler" leftover unburnt fuel to help carry away heat as it passes by the exhaust valve.

Part throttle it only takes 2-5% throttle and 8-12 hp to go 75mph ,thus not creating alot of heat, and allowing tuning to get to 14.0 or so for efficiency.

And the implications of how hot and crazzy a turbo header get with extreme back pressure...and the excessive A/F they use to ward off heat and detonation(11.0:1 or so,depending on boost/power production).

Being an engine tuner and dyno operation for sportbikes and such for 9 years, there is always crossover applications and designs that midigate each rule of thumb.

As far a exhaust flow goes, as the pulse wave goes down the tube there is a low pressure field behind it, if timed right where the 4-2 section is,the next explosion dumps right behind in this area and gets pulled along and so on.......alight them wrong and the pulses collide....which they will depending on the speeds(rpms), so certain systems can make smooth power 4-2-1-2 or top end effective 4-1.
 

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I am confused by this post first you say they need back pressure to keep hot exhaust gasses to keep the valve cool? wouldn't it make it hot, cause exhaust gases are hot? Then you say it needs to be less restricted? And how do the exhaust pulses compliment each other to create efficiency?
YES you are...thank yourself for that and stop looking into shervinn's book of exhaust ideas before you post next time.....:lol: ince you seem to know the answer to all your questions already then what the hell was this thread started for? our opinions? well then, i just gave ya mine.:mrgreen:...members are actually here to try and give you their thoughts and ideas but all you can do is come back with smarta$$ comments and know it all replies o why not figure it out for your damn self. to me your idea sounds like ALOT of work for a little IF ANY gains in the end...that would equal out to a total waste of time...kinda like this thread!!
 

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YES you are...thank yourself for that and stop looking into shervinn's book of exhaust ideas before you post next time.....:lol: ince you seem to know the answer to all your questions already then what the hell was this thread started for? our opinions? well then, i just gave ya mine.:mrgreen:...members are actually here to try and give you their thoughts and ideas but all you can do is come back with smarta$$ comments and know it all replies o why not figure it out for your damn self. to me your idea sounds like ALOT of work for a little IF ANY gains in the end...that would equal out to a total waste of time...kinda like this thread!!
:+1: Nicely put.
 

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Discussion Starter #18
Cool, guess i can do 421 header and have a bypass for higher rpms to go 4 to 1. Do you know anything about primary size and length ? what would be good set up? Thanks
 

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Discussion Starter #19
Dude your a smart ass. You know what i was saying. But please Go be a retard with whatever you want To do. I could careless I Was just trying to give you a tip. Sorry I chimed in. If u wanna make less power go ahead dumbass.
you have headerS on your inline 4 and I am the dumbass? I asked for opinions from people with knowledge or who have tried something similar, if you are not sure well your ideas would make things more confusing. I am trying to get my exhaust speed up to 240 feet per second.
 

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Discussion Starter #20
YES you are...thank yourself for that and stop looking into shervinn's book of exhaust ideas before you post next time.....:lol: ince you seem to know the answer to all your questions already then what the hell was this thread started for? our opinions? well then, i just gave ya mine.:mrgreen:...members are actually here to try and give you their thoughts and ideas but all you can do is come back with smarta$$ comments and know it all replies o why not figure it out for your damn self. to me your idea sounds like ALOT of work for a little IF ANY gains in the end...that would equal out to a total waste of time...kinda like this thread!!
Thanks for your input, it might turn out that way, weight and difficulty tuning is what i am worried about.
 
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