Exhaust Pressure Relief Control Valve?

[BenR]

Has anybody done any experimenting with putting an exhaust pressure relief valve on the exhaust just prior to the muffler? Something that would begin to open up once optimum torque is reached? Perhaps that same torque could be trailed off more slowly with the increasing RPMs with a spring loaded valve that begins to open up once the exhaust back pressure becomes the main hindrance to output.

 

[bigbird]

To answer your question, no I haven't.
Sounds like the risk, cost, and aggravation would be way more than the reward.
There is a company that makes what you're talking about; perhaps you could order a custom setup from them:

About The Jekill and Hyde Company

We want to give motorcyclists the ultimate biker experience with an exhaust second to none in regards to performance, power and esthetics. Read our story....

www.jekillandhyde.com

 

[bigbird]

When I put my Delkevic can on my bike, I was surprised that the force and volume of gas exiting the can was very little more or the same as that of the stock muffler.
That observation makes me believe that the exhaust manifold and cat converter are supplying the bulk of the restriction, rather than the muffler itself.
Any other bike I have put a straight-through can on has exhibited a dramatic increase in force and volume of gas exiting the can.
My conclusion is, only put a straight-through can on an NC if you want a better sounding exhaust, not for any increase in power or efficiency.

 

[670cc]

When I put my Delkevic can on my bike, I was surprised that the force and volume of gas exiting the can was very little more or the same as that of the stock muffler.
That observation makes me believe that the exhaust manifold and cat converter are supplying the bulk of the restriction, rather than the muffler itself.
Any other bike I have put a straight-through can on has exhibited a dramatic increase in force and volume of gas exiting the can.
My conclusion is, only put a straight-through can on an NC if you want a better sounding exhaust, not for any increase in power or efficiency.

The cylinder head design of the NC is unique in that there is one intake that splits to four intake valves, then four exhaust valve paths all merge into one exhaust outlet in the head. While I have no data to share on air flow characteristics, I think anyone attempted to modify the NC for more air flow should consider first the basic engine design they are dealing with.

 

[DirtFlier]

And all those intake and exhaust passages are cast into the head and not done as removable pieces. it's not a design that would yield significant improvements to a reduction in back pressure.

..and if you want more power, just add the Flux Capacitor option from HRC...just kidding.

 

[brb]

Exhaust valves are used to allow high flow, less restriction (higher rpm h.p.). While also allowing low flow, more restriction(lower rpm torque). To try to re engineer what Honda has already done would be a waste of time and money. If you want to change the exhaust to hear the motor more that would be for personal reasons only. When these exhaust valves are used by MFGs it is always to give better torque down low without hurting top end power. In the 80s the 2 stroke motocrossers used exhaust valves to change the exhaust port height for this same reason.