Engine Tuning - Intake/Exhaust Tuning Using Port Pressures

[nitro2]

This thread, at least at the start, goes along with the Engine Tuning - In Cylinder Pressure - Naturally Aspirated thread, in that the intake and exhaust port pressures (pressure wave tuning) are shown for the 8000 rpm 355 ci NA engine discussed in that thread. The data being shown is for the conventionally tuned engine prior to any cylinder pressure or intake/exhaust tuning.

The screenshot below shows the pressures measured in the intake and exhaust ports relative to crank angle, at about 7900 rpm.

Pressure is in psi on the y-axis, crank angle (2 full revolutions) on the x-axis, valve events and corresponding vertical lines across the top.

The intake port pressure is the blue line, the exhaust port pressure is the red line.

Going from left to right along the top you have TDC-C (TDC combustion), EVO (exhaust valve opening), BDC, IVO (intake valve opening), TDC (overlap) EVC (exhaust valve closing), BDC, IVC (intake valve closing) and back to TDC-C (TDC combustion for the next cycle).

Intake and Exhaust Port Pressures vs Crank Angle - NA - 355 c.i. - 7900 rpm

NA 355 ci - Cyl 1 - Intake and Exhaust Pressure - Example 1.jpg

[nitro2]

Below is a video, for the same engine, showing the intake and exhaust port pressure waves and how they change with rpm, going from 5700 rpm to 7900 rpm.


NA 355 ci - Cyl 1 - Intake and Exhaust Port Pressure Video
https://app.photobucket.com/u/nitro1385 ... 0d9b5f3da8

[nitro2]

The video and screenshot show the port pressures for the engine as is (i.e. conventionally tuned). These port pressures over the rpm band are better (magnitude and timing) than what we often see from a conventionally tuned engine, but still they can be improved upon. Any comments or questions about the traces ?

Just as a refresher from the other thread (Engine Tuning - In Cylinder Pressure - Naturally Aspirated), the indicated torque vs rpm for CYL 1 for this engine looks like this:

CYL 1 - Indicated Torque vs RPM (as determined from cylinder pressure)

NA 355 ci - Cyl 1 - Torque vs RPM.jpg

[SchmidtMotorWorks]

How about the range 6200 to 6800, the IT is more stable.

[nitro2]

How about the range 6200 to 6800, the IT is more stable.

"Stable" is one word for it. Basically 6200-6800 rpm has no "good combustion cycles" in it, so no cycles with stellar torque. It is desirable to have has many good combustion cycles as possible.

[nitro2]

While it is not possible to have the pressure in the intake port positive during overlap for this large of an rpm range, note how the intake and exhaust systems manage to keep the pressure in the intake port substantially higher than the pressure in the exhaust port, for the entire rev range.

It is possible to do a fair bit better than that, but for a conventionally tuned engine (that had never been instrumented with port pressure sensors before), this engine as is was better than most.


NA 355 ci - Cyl 1 - Intake and Exhaust Port Pressure Video
https://app.photobucket.com/u/nitro1385 ... 0d9b5f3da8

[SchmidtMotorWorks]

While it is not possible to have the pressure in the intake port positive during overlap for this large of an rpm range, note how the intake and exhaust systems manage to keep the pressure in the intake port substantially higher than the pressure in the exhaust port, for the entire rev range.

It is possible to do a fair bit better than that, but for a conventionally tuned engine (that had never been instrumented with port pressure sensors before), this engine as is was better than most.


NA 355 ci - Cyl 1 - Intake and Exhaust Port Pressure Video
https://app.photobucket.com/u/nitro1385 ... 0d9b5f3da8

Very nicely nearly perfecting offset parallel from IVO to EVC

[fordified]

This thread, at least at the start, goes along with the Engine Tuning - In Cylinder Pressure - Naturally Aspirated thread, in that the intake and exhaust port pressures (pressure wave tuning) are shown for the 8000 rpm 355 ci NA engine discussed in that thread. The data being shown is for the conventionally tuned engine prior to any cylinder pressure or intake/exhaust tuning.

The screenshot below shows the pressures measured in the intake and exhaust ports relative to crank angle, at about 7900 rpm.

Pressure is in psi on the y-axis, crank angle (2 full revolutions) on the x-axis, valve events and corresponding vertical lines across the top.

The intake port pressure is the blue line, the exhaust port pressure is the red line.

Going from left to right along the top you have TDC-C (TDC combustion), EVO (exhaust valve opening), BDC, IVO (intake valve opening), TDC (overlap) EVC (exhaust valve closing), BDC, IVC (intake valve closing) and back to TDC-C (TDC combustion for the next cycle).

Intake and Exhaust Port Pressures vs Crank Angle - NA - 355 c.i. - 7900 rpm

NA 355 ci - Cyl 1 - Intake and Exhaust Pressure - Example 1.jpg

This is very interesting. Thanks for sharing.

I'm working on a manifold for a 320" V8 drag racing engine with peak HP at 9500 RPM using a 4th harmonic runner. It would be interesting to put a probe where the runner meets the plenum and measure if the wave is exiting correctly given the port area and length.

What I cannot understand in the video why/how the pressure wave rises and falls between intake close and open. It seems to me that once the valve closes, the wave should rise toward ambient pressure and not fall below it. That is to say I would expect the only time it would fall below ambient is when the valve opens.

What am I missing? What was the location of the probe and what units are used for the Y-axis?

Is the pressure wave of the cylinder being influenced by the pressure waves of the other cylinders? I would expect the wave to dissipate once it reaches the plenum but that may not be the correct assumption since theres a lot going on in the plenum.

[naukkis79]

[
What I cannot understand in the video why/how the pressure wave rises and falls between intake close and open. It seems to me that once the valve closes, the wave should rise toward ambient pressure and not fall below it. That is to say I would expect the only time it would fall below ambient is when the valve opens.

What am I missing? What was the location of the probe and what units are used for the Y-axis?

As pressure in intake is much over ambient after IVC, that pressure makes flow from intake to atmosphere. That outflow makes vacuum to intake manifold which then starts new inflow and cycle starts again. That's harmonics, and if intake is tuned to some harmonic that means how many cycles happen between IVC and IVO. That graph above shows that tune in that point is in exactly at second harmonic.

[SchmidtMotorWorks]

"What am I missing? What was the location of the probe and what units are used for the Y-axis?"

I think the probe is positioned as close to the valve as possible.
The pressure builds as the piston rises in opposition to the inertia of the column of air in the intake duct.
The valve closes when it can trap the most air possible.

[JoePorting]

I see this as being more of flow pulses flowing up and down each port. Best example of this is when Jon Kaase did that video where he stuck his finger in the intake port runner. His finger was moving so fast back and forth you couldn't tell which direction the air was going.

I would think the pulses would change over the rpm range, but they don't. I noticed the back and forth motion of Jon Kaase's finger didn't change throughout the rpm either. I assume these pulses are a function of the cylinder head design. I would think a raised runner head would have less severe pulses which is what makes them work better and make better power, IMO. I also notice the exhaust pulse is more severe than the intake pulse which make me think the exhaust efficiency, or lack of efficiency, is causing these pulses.

[naukkis79]

Pulses are coming from pressure differentials - higher pressure higher pulses. Exhaust has way more pressure than intake, intake pulse is coming from atmospheric pressure no there's a hard limit of how strong pulse can be. Pressure differential is driving force, flow path measures how fast air can be accelerated, so straighter flow path stronger pulses. A key to tuning is how much vacuum can be made in intake cycle before incoming flow starts, that's visible in those traces at about 90 degree. Vacuum dictates to which speed incoming flow in runners are accelerated, and to how much pressure is achieved before flow reverses. Mach1 speed is achieved at about 0.45 bar pressure differential, about 6psi vacuum. Mach1-speed potential is there with 6psi pressure differential, not every runner is capable of flowing at full Mach speed.

It can be demonstrated with vacuum canister, attach tube to vacuum canister and make vacuum to it, unblock tube and see how incoming flow makes harmonics to tube end after inrush. Those pulses are pretty violent.

[nitro2]

How about the range 6200 to 6800, the IT is more stable.

"Stable" is one word for it. Basically 6200-6800 rpm has no "good combustion cycles" in it, so no cycles with stellar torque. It is desirable to have has many good combustion cycles as possible.

To take this a bit further though it is probably better discussed in the cylinder pressure thread, and I think I'll copy it over there, the fact that there are no "really good combustion cycles" 6200-6800 rpm but there are some "really good combustion cycles" at other engine speeds, this is actually a huge bonus because when you figure out why there are no "really good combustion cycles" at 6200-6800 rpm and what you need to do to get some, then you are halfway to the jackpot.

Those "really good cycles' that make more extra torque, they aren't wishful thinking, they are not only attainable a high percentage of the time, but there's a whole level of combustion and torque that exists above those "really good cycles" that are also attainable without even increasing VE. I'll get into that in the cylinder pressure thread.

[nitro2]

I would think the pulses would change over the rpm range, but they don't. I noticed the back and forth motion of Jon Kaase's finger didn't change throughout the rpm either. I assume these pulses are a function of the cylinder head design. I would think a raised runner head would have less severe pulses which is what makes them work better and make better power, IMO. I also notice the exhaust pulse is more severe than the intake pulse which make me think the exhaust efficiency, or lack of efficiency, is causing these pulses.

The pulses do change some with rpm but this minimal(ish) change is not typical of most engines, the point of this is to make a high and wide powerband race engine. The pulses change a lot more with rpm for narrow powerband race engines, and also for engines less well thought out. I will post some later when I get through with this engine.

The intake/exhaust pulses for this engine are actually not all that big in magnitude. A build with more power will absolutely have BIGGER pulses, much.

An engine with no pulses is not running. An engine with small pulses will make no power, think stock 318 smog engine lol. The goal (well one of the goals) from a torque/power standpoint is to INCREASE the pulse magnitude.

I wonder if Jon's finger is cheaper than a pressure sensor ? I'm guessing it isn't

[SchmidtMotorWorks]

How about the range 6200 to 6800, the IT is more stable.

"Stable" is one word for it. Basically 6200-6800 rpm has no "good combustion cycles" in it, so no cycles with stellar torque. It is desirable to have has many good combustion cycles as possible.

I was thinking that good combustion cycles were still kind of rare and that perhaps it would be easier to smooth it out first, and then figure out how to turn it up.