Engine Tuning - Intake/Exhaust Tuning Using Port Pressures

[SchmidtMotorWorks]

I noticed the back and forth motion of Jon Kaase's finger didn't change throughout the rpm either.

Kaase's finger has too much mass to follow the direction of the multiple pulses.

Think of a boat on rough water, it bounces but doesn't follow any one wave.

[digger]

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

Seems like a fairly large suction wave magnitude, I thought 0.5b would be more likely

[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

Seems like a fairly large suction wave magnitude, I thought 0.5b would be more likely

0.5 bar (7.25 psi) suction would be a mediocre exhaust suction. The exhaust suction magnitude for this engine was pretty good, but I've seen better. The magnitude of the exhaust pressure peak during blowdown is fairly low, the magnitude of the intake pressure around intake valve closing is better than average, but definitely not stellar.

[digger]

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

Seems like a fairly large suction wave magnitude, I thought 0.5b would be more likely

0.5 bar (7.25 psi) suction would be a mediocre exhaust suction. The exhaust suction magnitude for this engine was pretty good, but I've seen better. The magnitude of the exhaust pressure peak during blowdown is fairly low, the magnitude of the intake pressure around intake valve closing is better than average, but definitely not stellar.

was more talking about common rather than good/bad.

id be surprised if most street strip kind of engines that don't have regimented development program are seeing 10psi suction

what is the configuration of this 4into1, Tri-Y, something else?

[nitro2]

Seems like a fairly large suction wave magnitude, I thought 0.5b would be more likely

0.5 bar (7.25 psi) suction would be a mediocre exhaust suction. The exhaust suction magnitude for this engine was pretty good, but I've seen better. The magnitude of the exhaust pressure peak during blowdown is fairly low, the magnitude of the intake pressure around intake valve closing is better than average, but definitely not stellar.

was more talking about common rather than good/bad.

id be surprised if most street strip kind of engines that don't have regimented development program are seeing 10psi suction

what is the configuration of this 4into1, Tri-Y, something else?

I don't recall the details on the exhaust, but it definitely was not Tri-Y.

I've seen 12 psi suction using a special exhaust, it's harder to come by, but worth it, particularly when you modify the engine to take advantage of it.

[MadBill]

...Any comments or questions about the traces ?...

Great to get the story 'straight from the horse's mouth' Clint!

Skipping by all posts subsequent to the above quoted one (to avoid confusing myself with facts):

• It appears that the exhaust 'optimum tune' RPM is ~ 6,000 whereas the intake is more like 7,000+ Since the 'window' for the former is much wider, I'd expect for most applications that reversing the tune ranges would yield more peak power and a wider band

• Including a cylinder pressure trace would be a good visual re port/cylinder pressure differentials.

[nitro2]

...Any comments or questions about the traces ?...

Great to get the story 'straight from the horse's mouth' Clint!

Skipping by all posts subsequent to the above quoted one (to avoid confusing myself with facts):

• It appears that the exhaust 'optimum tune' RPM is ~ 6,000 whereas the intake is more like 7,000+ Since the 'window' for the former is much wider, I'd expect for most applications that reversing the tune ranges would yield more peak power and a wider band

• Including a cylinder pressure trace would be a good visual re port/cylinder pressure differentials.

Well answering your last question first you need a very expensive sensor to accurately read the tiny cylinder pressures at overlap and when you do you realize you knew what the result would be all along without ever measuring it, so that is money not well spent. Rarely done unless it's for a tech paper or one happens to be using the very expensive sensors anyways. Having port pressure sensors and a bit of logic, will do the trick just fine.

There really is no optimum tune rpm for that exhaust, within the range of rpm being tested, because it does all it needs to do at overlap for the entire rpm range of the test. This cannot be said of many conventionally tuned exhausts, they tend to be in tune at some engine speeds and out at other engine speeds over their powerband i.e. one of the factors contributing to torque dips. As conventionally tuned exhausts go, this one is well done. Improvements can be made but changing the lengths to shift the tune rpm is not one of them.

When you are referring to the intake tuning at 7000+ rpm are you referring to what the intake is doing at overlap or what it is doing at IVC ? They are two different things.

[MadBill]

I was looking at overlap.

[nitro2]

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

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

[nitro2]

It appears that the exhaust 'optimum tune' RPM is ~ 6,000 whereas the intake is more like 7,000+ Since the 'window' for the former is much wider, I'd expect for most applications that reversing the tune ranges would yield more peak power and a wider band[/list]

The exhaust tuning range is a non-issue but I wasn't sure though what you meant about the intake, it reads like you want to tune the intake for 6000 rpm ?

[MadBill]

No, I meant that given the typically narrower 'tune band' for the intake system (and depending of course on the operational requirements, e.g. 5 speed vs Powergilde) it might be beneficial to have the intake length optimized for mid-range and the exhaust for peak or near-peak power.

[nitro2]

No, I meant that given the typically narrower 'tune band' for the intake system (and depending of course on the operational requirements, e.g. 5 speed vs Powergilde) it might be beneficial to have the intake length optimized for mid-range and the exhaust for peak or near-peak power.

You're making it tough to answer the question and not have someone get upset that I said more than I should.

Let's just say, in this case, no.

[MadBill]

Speaking of tough, I'm finding it challenging to parse that reply...

[nitro2]

Speaking of tough, I'm finding it challenging to parse that reply...

Diverging a bit, the slow drift down in VE with increasing revs indicates that nothing (head, intake, exhaust) has run up against a brick wall, there is more to be had at higher revs with the right changes using essentially the same equipment (i.e. same head).

The engine could be making more torque by improving the combustion. More power by improving cylinder filling at yet higher revs plus the added improved combustion. Conservatively 5% on combustion and 10% on revs as a start, so about 5 % more peak torque and 15% more peak power. Mind you the internals then need to be OK at 8800 rpm plus some amount of overrev, instead of 8000 rpm plus some amount of overrev.

One could always change the head too, but quite often that is either not desirable (cost), or not possible (rules), or might result in a narrow powerband engine (OK for some things and not OK for others).