Kx65 Pipe

[YetiWoodz]

Hmmm... maybe if I increase the diameter of the stinger, I can decrease the strength of the baffle wave and increase the strength of the diffuser wave. Does that sound like it would work to broaden the powerband or work better for mid rpms?

Quotes from dragonfly75

"Flared Header
Most headers on high RPM MX and GP bikes are divergent up to 2 degrees. That is to say that they get larger with more distance from the cylinder. This theoretically aids exhaust gas flow at high RPM which helps evacuate the cylinder pressure faster and also it aids in sucking up intake charge into the cylinder thru the transfers. But it does this at the expense of the main diffuser wave since that design causes the diffuser angle to be lessened. But still it has been a dyno proven method."

(Since I'm gonna tune it for mid rpms, I don't need the positive effect of the flared header. So by increasing stinger diameter, I could increase the diffuser wave strength that the flared header weakened.)

"The stinger determines the pipe back pressure which combines with the diffuser return wave to lessen it, and with the baffle return wave to increase it. The back pressure is relative to engine RPM so that it linearly increases to its peak value at peak RPM. Without any modification by back pressure the pipes return wave pressures from the diffuser and baffle remains the same though throughout the RPM range."

(Decrease baffle wave strength to broaden rpm range.)

 

[Street Ryderz]

Hmmm... maybe if I increase the diameter of the stinger, I can decrease the strength of the baffle wave and increase the strength of the diffuser wave. Does that sound like it would work to broaden the powerband or work better for mid rpms?

Quotes from dragonfly75

"Flared Header
Most headers on high RPM MX and GP bikes are divergent up to 2 degrees. That is to say that they get larger with more distance from the cylinder. This theoretically aids exhaust gas flow at high RPM which helps evacuate the cylinder pressure faster and also it aids in sucking up intake charge into the cylinder thru the transfers. But it does this at the expense of the main diffuser wave since that design causes the diffuser angle to be lessened. But still it has been a dyno proven method."

(Since I'm gonna tune it for mid rpms, I don't need the positive effect of the flared header. So by increasing stinger diameter, I could increase the diffuser wave strength that the flared header weakened.)

"The stinger determines the pipe back pressure which combines with the diffuser return wave to lessen it, and with the baffle return wave to increase it. The back pressure is relative to engine RPM so that it linearly increases to its peak value at peak RPM. Without any modification by back pressure the pipes return wave pressures from the diffuser and baffle remains the same though throughout the RPM range."

(Decrease baffle wave strength to broaden rpm range.)

Sorry but this just sounds like more of Micheal's misguided BS,He's contradicting himself there it's been dyno proven by real engineers that stinger dia has more to do with final peak and the audible level it produces along with the most important thing it does which is the heat retention.Heat in the pipe is a big part of the equation in finding the tuned length because less heat means slower less magnitude waves which will largely affect overall performance not just one area!Cone angles and their sizes are calculated for volume,flow rate at a given heat which determines how many meter's per second that pressure (the waves) travel so increase the stinger dia and lose heat which will slow the waves, reduce magnitude and affect pipe timing over all not just in one place.

 

[YetiWoodz]

Ok, thanks StreetRyders, that clears that up. I guess I'm just gonna leave my pipe how it is and just lengthen the header.

 

[YetiWoodz]

so say you have 160 exh duration x that by 1700 then divide by the peak 6500 = 41.8" total length,that's pretty low for a peak so the pipe is long (overall).

What does the number 1700 represent?

 

[Street Ryderz]

What does the number 1700 represent?

That's the wave speed and the feet per second it travels at.

 

[YetiWoodz]

In general, how soft/hard is the transition into the powerband? Like if the powerband were a graph would it have a steep slope or a gradual slope?

And does it just cut off at the ends of the powerband or does the pipe still slightly operate outside it?
Does any of this differ for dirt bike and scooter pipes?

 

[Street Ryderz]

In general, how soft/hard is the transition into the powerband? Like if the powerband were a graph would it have a steep slope or a gradual slope?
View attachment 99674View attachment 99675
And does it just cut off at the ends of the powerband or does the pipe still slightly operate outside it?
Does any of this differ for dirt bike and scooter pipes?

A good informative read is the two stroke tuners handbook or Bell's work's because there is alot to explain all you're asking about.A quick rundown though would be,how hard it hits depend's on where (rpm) and the angle of the baffle cone (convergent section) so the graph would vary also depending on design.The pipe can have an over run/rev usually about 1k from peak but this is where the wave timing start's to fall short which in turn leaves the cylinder fill short circuited (lean) and it falls off hard on the dyno graph.Yes dirt bike and scooter pipes are vastly different in design and then of course how they work,dirt bike pipes are designed to hit high and hard in the rpm for a narrow band width to aid in topping out each gear where the scooter pipes are designed to hit earlier and lower in the rpm over usually double the band width with some extra over run that the dirt bike pipes don't have they just fall off hard.

 

[YetiWoodz]

so say you have 160 exh duration x that by 1700 then divide by the peak 6500 = 41.8" total length,that's pretty low for a peak so the pipe is long (overall).

Just want to clarify. Is the peak in the equation supposed to be the target rpm (middle of the powerband) or the end of the powerband?

 

[Street Ryderz]

Just want to clarify. Is the peak in the equation supposed to be the target rpm (middle of the powerband) or the end of the powerband?

Peak being the highest point of power made and usually just before the pipe start's to fall off so the top of power band.

 

[Street Ryderz]

As you can see here pipes can vary greatly in how they work,the peak and amount of over run vary's alot!