ESE's works engine tuner

[wobbly]

JVH, just something to try - when the main port duration is 190* to 192* with the pipe length adjusted to suit, I have found more overall power
due to a naturally very wide band of superposition prior to EPO.
This may also allow more timing split with the Aux ports, so their differing ( longer ) duct length has less effect on the wave amplitude generated by the main port into the diffuser.
But this may not show up as a huge difference in EngMod as there is no mechanism in the code to define the Aux ports duct length, only an assumption on my part - dangerous.

[Vannik]

JVH, just something to try - when the main port duration is 190* to 192* with the pipe length adjusted to suit, I have found more overall power due to a naturally very wide band of superposition prior to EPO.

This is the difference between a resonating pipe and a tuned pipe:

1. A tuned pipe is a pipe where the pressure pulse reflected from the reverse cone arrives in time to push over scavenged fresh charge back into the cylinder;

2. A resonating pipe is a tuned pipe that builds stronger pulses by combining the new pulse with the residual pulse from the previous cycle to build pulses and suction pulses of substantially higher amplitudes.

[Jan Van Hamme]

This is the difference between a resonating pipe and a tuned pipe:

1. A tuned pipe is a pipe where the pressure pulse reflected from the reverse cone arrives in time to push over scavenged fresh charge back into the cylinder;

2. A resonating pipe is a tuned pipe that builds stronger pulses by combining the new pulse with the residual pulse from the previous cycle to build pulses and suction pulses of substantially higher amplitudes.

Months ago, I read somewhere on a forum, perhaps here or on Facebook, that an exhaust only starts working properly at timings of 190°. I have no idea why.
With this in mind, I tried first 185°. It produces a better power curve than the single exhaust port. So I thought, yes, 185° will be fine.
With your explanation Neels, I now understand what I read about 190°. A pipe will probably only starts resonating at 190°.

I'll definitely try that in Engmod.

Just a question for information. I learned in Mechanics that when designing machines, engines, bridges, etc., you have to pay attention to the natural frequencies of the structure.
When the load or operating conditions generate a frequency close to or at the natural frequency of the structure, this leads to total failure.
For example, as everyone knows, a platoon of soldiers shouldn't walk across a bridge in rhythm, or the bridge could resonate and bend further and further until it breaks.
This applies to solid matter, but apparently a gas can also resonate? A resonating exhaust.
Apparently, those resonating gases don't cause fracture.

I once read from Frits that the waves in a 2-stroke exhaust are not the same as the sound waves in a trumpet, for example.
Difficult material for me to dig deeper into.

In any case, I'm going to try a 190° version in Engmod and then come back here.

[Wos]

"No idea at all how many degrees of difference there should be between main and aux ports"

JVH... why go to a limit with the bridges on a triple exhaust when you have much chances to gain enougth blowdown. ..?
Stay on the save side and gain long reliability!? Thats nice to have



If i remember coreectly once frits told us 5 degree for every bridge between every port in a cilinder ...

Such a nice thing like a printed cilinder...them i would change case transfers too
Maybe, if case is sturdy...only a big one per side!? So you are more free with directions of cilinder transfer !? good thing ...

Grüße Wolfgang

[Jan Van Hamme]

"No idea at all how many degrees of difference there should be between main and aux ports"

JVH... why go to a limit with the bridges on a triple exhaust when you have much chances to gain enougth blowdown. ..?
Stay on the save side and gain long reliability!? Thats nice to have



If i remember coreectly once frits told us 5 degree for every bridge between every port in a cilinder ...

Such a nice thing like a printed cilinder...them i would change case transfers too
Maybe, if case is sturdy...only a big one per side!? So you are more free with directions of cilinder transfer !? good thing ...

Grüße Wolfgang

I think you misunderstood my question. I meant the difference in height between the main and auxiliary levels. Not the degrees that represent the width of the bridges.
Wobbly already pointed me in the right direction and answered.
Thanks anyway.

Groeten Jan

[Frits Overmars]

I once read from Frits that the waves in a 2-stroke exhaust are not the same as the sound waves in a trumpet, for example.

The waves are essentially the same. Waves moving through a gas are local compressions of the gas where the molecules are closer together.
Compare it to circular waves on the water surface when you throw a stone into a pond. You see that the wave tops move outwards from the point where the stone hit the water, even though the water itself does not move, which you can see by looking at what is floating on the water.

The difference between exhaust pulses and a trumpet sound is not in the nature of the waves, but in the way you can describe their behavior.
For the trumpet sound you can use acoustic rules. And I deliberately write acoustic RULES and not acoustic LAWS because they are not laws. Those rules are derived from gas dynamics laws, simplified with a lot of assumptions that are acceptable as long as the sound pressure does not exceed a certain limit.
The wave pressures in a two-stroke exhaust exceed that limit by a factor of over a thousand. So forget about acoustics when you are dealing with waves in exhaust systems.

Now you may remember where you read it Jan .

[Jan Van Hamme]

JVH, just something to try - when the main port duration is 190* to 192* with the pipe length adjusted to suit, I have found more overall power
due to a naturally very wide band of superposition prior to EPO.
This may also allow more timing split with the Aux ports, so their differing ( longer ) duct length has less effect on the wave amplitude generated by the main port into the diffuser.
But this may not show up as a huge difference in EngMod as there is no mechanism in the code to define the Aux ports duct length, only an assumption on my part - dangerous.

Main exhaust timing adjusted to 190°, main to aux = 3,8° instead of 2,3°.
Transfers and blowdown fully balanced. Pipe tuned lenght to 10k exactly.

Result: bmep rises from 13,58 @ 185° to 13,93 @ 190°.
1hp more but...lost a lot of front and mid power.

[Jan Van Hamme]

Now you may remember where you read it Jan .

Indeed. You can't imagine all the things I've read from you.
But remembering it all...that's no longer possible at 55.