Exhaust Science

[Neville Lush]

"larger-radius, higher-flowing bends" this comes out of that article, which seems like a good article. BUT that statement is not true. Look up Micron exhausts ( from the past) and laminar flow concept and find out why.

 

[Claviger]

Area under the curve is king on the street for fun factor.

Peak is king on the track.

A properly sized pipe will give both more lower end torque and more power up top than a too small pipe and only lose out by a handful of HP up top to an oversized pipe.

The main lesson: anything 1 5/8" to 2" will work for a broad power curve on a rocket and the factory stuff flows like ****e!

The real magic comes in Primary length not diameter!

 

[mully95]

I have a supertrapp muffler on the end of a Viking exhaust header. The end cap I use has a about a 1 1/4" hole in it. Without a cap the pipe is 2" straight through.

If I remove the cap my torque seems to fall off..... going by butt dyno. Install it ... it all comes back.

It's a trip how a small amount of change can make a difference. My bike likes a little bit of back pressure.

 

[Speedy]

"larger-radius, higher-flowing bends" this comes out of that article, which seems like a good article. BUT that statement is not true. Look up Micron exhausts ( from the past) and laminar flow concept and find out why.

Well, that depends. It is a little more complicated than what Micron's propaganda states. How fast is too fast? When does a venturi, which is what they create with their "serpent," reduce power? Why? Where are they best placed? Why not make the entire pipe small and keep velocity high all the way to the exit? Sometimes "larger-radius, higher-flowing bends" are better.

 

[warp9.9]

I don't always know something!!!!!!!!

But when I do, I know Nothing

 

[Neville Lush]

Speedy, It is not a venturi, the bend at the start has the same cross sectional area as the header pipe. By having a very short turn the eddying of gas which occcurs on the inside of a bend is limited to a much shorter distance, in the area of the pipe where the fastest gas speed is. It is an illustration of the effect of how eddying/turbulence effects flow. Mully, you can notice the change for sure. If you were to tune the bike exactly with each configuration, it would be apparent which is better. Obviously not everyone can do this ,as it is costly, it may lose torque because the change throws off the tune, or it may as you say , just need a smaller hole.

 

[cootertwo]

In my feeble old mind, it all depends on what you want to do. 1/8 mile drag, 1/4 mile drag, Texas mile, or Bonneville, or to the diner and back home. Each one would require a different setup to be at peak performance.

 

[Speedy]

Speedy, It is not a venturi, the bend at the start has the same cross sectional area as the header pipe. By having a very short turn the eddying of gas which occcurs on the inside of a bend is limited to a much shorter distance, in the area of the pipe where the fastest gas speed is. It is an illustration of the effect of how eddying/turbulence effects flow. Mully, you can notice the change for sure. If you were to tune the bike exactly with each configuration, it would be apparent which is better. Obviously not everyone can do this ,as it is costly, it may lose torque because the change throws off the tune, or it may as you say , just need a smaller hole.

Neville, if the cross-section in the pipe is reduced at all on entry to , through the center section, and increased at the exit of the serpent it is a venturi. If the cross-section is not reduced, the surface area of the passage is, has to be, increased which increases boundary layer area thus reducing flow. There is a trade off here. I do not disagree that this technique is effective in some cases. Almost exclusively where a severe bend is located near the exhaust port because of space constraints.

The horizontal "D" shaped exhaust port in many heads attempts to perform the same task. By raising the port floor the bend's inside radius grows in length and port cross-section area is reduced, all to reduce eddy flows. Nothing new there: been done since WWII. Still, why not put a serpent at the second major bend found in most cycle headers too?

Micron's serpent, or a venturi, or even a reverse venturi, also changes shock wave profile and propagation in the pipe. And then these devices separate to a degree the upstream and downstream pressure wave activity after the initial shockwave traverses the length of the system. This effect may have as much (likely more) to do with the performance differences found as the reduction in eddies and resultant increased flow rate from using a serpent.

I took exception to your statement that larger radius, higher flowing bends are not better. Nothing more.

 

[Joesmoe]

Beautiful to see true intellect and passion on display here. Thank you both !

 

[barbagris]

............

Oh man - yes - talk dirty to me.

iirc - I made some pipes up for a Guzzi in the mid 80's. Primary length and header bore determines the Shock wave speed and resonance. Swept volume (including primary chamber of end pipe) affects how wide the torque band is. I run Jardine headers with the "Predator" CNC manifold - upped midrange torque a bit - but eventually stifles as it exits reduced to mate with Standard pipes (should one so wish). But my guess is that 90% of us (me included) ride at less that 20% throttle most of the time so real world - it's all a bit moot.