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Does quench affect power?

General engine tech -- Drag Racing to Circle Track

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Re: Does quench affect power?

Post by hoffman900 »

LotusElise wrote: Tue Sep 20, 2022 8:30 am
ptuomov wrote: Tue Sep 20, 2022 7:43 amI don't think one can infer much anything about the squish height during the combustion TDC from the piston to head clearance during overlap TDC. Inferring the squish height at combustion TDC from piston to head clearance at overlap TDC will give you the wrong squish height and consequently the wrong squish velocity.
That's a very good point, I have a simple model of that in my rod bolt force model which tells me with respect to IGT and VE as well as some Vibe parameters how much that is, just not integrated into my squish design model. To give you a feeling how much we talk about on a 2-Liter NA race engine at a VE of 120 % at redline: 0.35/1 (gas force/rod bolt forces), so only a partial compensation.
ptuomov wrote: Tue Sep 20, 2022 7:43 amThere's a separate question of what role squish plays in a high-performance four-valve engine. My opinion is that one is better off prioritizing tumble and that leads to basically no squish, beyond what is incidentally created by the need for a high compression ratio. My opinion is that well-guided pure tumble that is broken down into small eddies at the combustion TDC is the best solution for high rpm, WOT operation of a performance engine. But that's just an opinion.
Tumble is the most inefficient kind of combustion processing. Formula 1 had long time issues to exceed the 12,000 rpm. With introducing of proper squish they found the way up to 20,000 rpm on 90+ mm bores.
How sure are you of this and can you back it up, because this flies in the face of Honda’s white papers, SAE papers, and just about everything else. Also, F1 realized the way to get there was with higher and higher injection pressures.
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Re: Does quench affect power?

Post by ptuomov »

LotusElise wrote: Tue Sep 20, 2022 8:30 am
ptuomov wrote: Tue Sep 20, 2022 7:43 amI don't think one can infer much anything about the squish height during the combustion TDC from the piston to head clearance during overlap TDC. Inferring the squish height at combustion TDC from piston to head clearance at overlap TDC will give you the wrong squish height and consequently the wrong squish velocity.
That's a very good point, I have a simple model of that in my rod bolt force model which tells me with respect to IGT and VE as well as some Vibe parameters how much that is, just not integrated into my squish design model. To give you a feeling how much we talk about on a 2-Liter NA race engine at a VE of 120 % at redline: 0.35/1 (gas force/rod bolt forces), so only a partial compensation.
It was Nitro2's point from a couple of pages up.

Even if the rod bolts stretch at TDC combustion, does the whole reciprocating assembly have to stretch as much? How do the combustion and inertial forces net out in the whole piston, pin, rod, bolt assembly?
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Re: Does quench affect power?

Post by LotusElise »

hoffman900 wrote: Tue Sep 20, 2022 8:43 am How sure are you of this and can you back it up, because this flies in the face of Honda’s white papers, SAE papers, and just about everything else. Also, F1 realized the way to get there was with higher and higher injection pressures.
Maybe I should have been more precise, I was a bit short on time. Maybe I start with an simple comparison. While swirl survive a up moving piston and get even concentrated to the center by squish, if there, and create a nice TKE increase (= micro vortex energy) much of tumble get dissolved in friction when the macro rotating mixture see the piston coming up. The efficiency invest of energy in form of PMEP into TKE is bigger on a swirl compared to a tumble.

On top of that both forms of flow regime get of lower contribution once engine speed increases. At about 6000+ rpm, may differs on different engine designs, so kind of magnitude here only, swirl and tumble are neither affecting emission build up nor performance. Background is inertia of the mixture reduces the willingness of gas molecules to follow the piston speed- to rotational speed-ratio, it get reduced with increasing speed. You will have a hard time to find a race engine running above 8000 rpm with an swirl flow regime. Tumble you will find many, but those don't count as squish is the dominant TKE source, which increases system immanently with engine speed.

In 2010 I was involved in a new combustion process design development. During that many wanted to introduce tumble, as it would be easier on that 4-valve head, the swirl ports where complex and price was a demand of a higher boost level for the certain power level compared to tumble. The problem with tumble could be seen in the 3D CFD and at the single cylinder bench, it creates a strong TKE at IGT, but looses too fast it's level as it dissolves too fast in friction, which don't contribute pushing the flame front strongly further down the radius. That mean a less advanced knock margin (up to 4°ca difference) and finally a higher boost level as the combustion efficiency of the 50-90 % mass fraction burnt was way down. That meant more NOx and more CO emissions. As I've seen very early in the process I invented a new combustion process, based on squish and swirl and this went finally in series. Over 3000 engines are out at customers with that combustion process design and made for that company clear, big bore flat head 4-valve chambers can't be tumbled, they need swirl and squish to empower combustion in a smart kind of: slow when NOx build up is prone to and fast when the combustion get challengend by the increasing surface/radius and loose heat and turbulence.

On a fast reciprocating engine, let's say redline is at 11,000 rpm, has system immanently a higher rod-stroke-ratio of 1.8:1 and more. Assuming a typical 500 ccm chamber one would need to feed 10,000 rpm peak power right with an valve size of 36-37 mm for 2 intake valves and around 30-31 mm for the two exhaust valves. Even if one has an 90 mm bore and a 78.5 mm stroke, those valves need around an inclined valve angle of around 40°. You can't design a 13:1 CR into that chamber without a positive dome, at least by 5+ ccm. That is a tumble killer.

If you look into the extreme narrow included valve angles of F1 engines and necessary bores of 96-100 mm bore the effective chamber get so inefficient that squish is the only supporter of combustion and they still had positive dome volumes because of their 2.4+:1 rod stroke ratios. Those piston have, except the valve relieves, only squish areas. The steep port angles were only designed for VE support. At 20,000 rpm, which was the upper edge of the BMW V10 was operated, only 0.38 ms are available to run from spark plug to liner wall at an average speed of 131 m/s. You need to feed that roughly 300 ccm chamber in 0.7 ms! If there is a tumble rolling only one time at a radius of 40 mm, that would mean a tangential velocity of 186 m/s, at 20 mm it would may fit with 93 m/s the loss through cornering friction. Try to calculate the centrifugal force at 93 m/s on a 20 mm radius, you will see tumble is an illusion there. You can't do that only on tumble, that can only be done with squish, tumble plays an under carpet role in that high speed game.
DAMPFHAMMER engine:
2000 ccm, Honda K20 NA engine
4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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Re: Does quench affect power?

Post by ptuomov »

The moving charge that fills the cylinder has some amount of kinetic energy in it. The way I've understood it from reading large eddy simulation results is that tumble is useful in preserving that kinetic energy until near the TDC where it can then be broken into the kind of turbulence that is useful in speeding up the combustion. This breakup works well if the combustion chamber becomes compact at TDC.

The reasons why I am skeptical about squish in high performance, high rpm, high R&D budget, four-valve engines is that, if they have a low compression ratio and therefore design flexibility on combustion chamber shape, they mostly have spherical dish pistons. They don't have squish pads. This to me indicates they prioritize preservation of tumble over squish where there's a real design choice to be made between tumble preservation and squish.
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Re: Does quench affect power?

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ptuomov wrote: Tue Sep 20, 2022 11:10 am The moving charge that fills the cylinder has some amount of kinetic energy in it. The way I've understood it from reading large eddy simulation results is that tumble is useful in preserving that kinetic energy until near the TDC where it can then be broken into the kind of turbulence that is useful in speeding up the combustion. This breakup works well if the combustion chamber becomes compact at TDC.
Yeah, that is also what I have gathered. The impulse of the port flow is essential for the TKE production. Of course swirl and tumble flow regimes contribute to that, my point is the higher the engine speed the less it does come from their side because of the inertia of the fresh mixture. As I wrote from a certain engine speed on swirl can be neglected or even negative by extracting fuel droplets out of the mixture, throwing onto the liner wall. Same is valid for tumble. Squish is then an option to bring the fuel back into the game.

I see your point, V8 engines has system immanently longer rods and especially with Cup engines quite high strokes. Back in the days when they still revved to 10,000 rpm with 82 mm stroke and huge bores of around 106 mm it is clear that the flat head design with those inclined valve angles of 12°-18° have almost no volume in the head and thence negative dome volume in the pistons. These 2-valve heads - as far as I know - are prone to have swirl, so it is not far from rationality to use it or improve it to what fits best.

Image

Mostly they utilize the very compact wedge design, providing huge squish area, therefore, we talk always about squish velocity as design parameter, the squish height is accordingly, not to increase squish velocity much above to what the combustion needs. Aren't these NASCAR CUP engines limited to 12:1 as CR?
ptuomov wrote: Tue Sep 20, 2022 11:10 amThe reasons why I am skeptical about squish in high performance, high rpm, high R&D budget, four-valve engines is that, if they have a low compression ratio and therefore design flexibility on combustion chamber shape, they mostly have spherical dish pistons. They don't have squish pads. This to me indicates they prioritize preservation of tumble over squish where there's a real design choice to be made between tumble preservation and squish.
About which kind of race series and engine do you have in mind where your skeptics about squish cam from?
DAMPFHAMMER engine:
2000 ccm, Honda K20 NA engine
4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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Re: Does quench affect power?

Post by ptuomov »

Porsche 4-valve turbo engines, AMG/MB M139 2L turbo, Koenigsegg V8, etc. I believe they have spherical dish pistons with a band that’s not matched with the head to produce squish. But they of course do break up the tumble into smaller turbulent eddies as the combustion chamber gets compact with the piston coming up.
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Re: Does quench affect power?

Post by David Redszus »

Even without a clearly defined squish pad (as in a hemi), piston motion still creates significant charge motion.
As the piston moves upward on the compression stroke, it scrapes the air (and fuel) from the cylinder wall.
Where does this air go and at what velocity?

All the squish calculations (including mine) are actually approximations which do not reflect true
closed cycle turbulence, either BTC or ATC.

And the actual squish induced turbulence is always engine specific reflecting chamber and piston dome.

When dealing with matters of great complexity, it is normal to simplify to assist understanding.
But that comes with a substantial loss of accurcy and often even with misdirection.
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Re: Does quench affect power?

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A friend of mine wrote his mechanical engineering thesis on the internal combustion engine.
In it, as published, was stated that the best combustion chamber was a sphere with it's ignition source in the centre.

As far as I know, several decades later it's still not possible to have the spark originate in the centre of a sphere, although it does lend some credence to having a dished piston and hemispherical chamber wouldn't you think? No squish.

His paper, not mine although the thought has stuck with me all these years.
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Re: Does quench affect power?

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ptuomov wrote: Tue Sep 20, 2022 7:58 pm Porsche 4-valve turbo engines, AMG/MB M139 2L turbo, Koenigsegg V8, etc. I believe they have spherical dish pistons with a band that’s not matched with the head to produce squish. But they of course do break up the tumble into smaller turbulent eddies as the combustion chamber gets compact with the piston coming up.
Those are all emission driven combustion process designs. Fast combustion is a NOx production lever arm, which is not the aim in todays EURO 6d+ compliant engines. You can't put them in a row of high performance engines. If they design it just for track it would look a bit different.

I developed over 6 different OEM combustion process designs which are running in series. I know quite good the challenges on emissions, and what you don't want is a NOx-production combustion process, as the cost on the aftertreatment is impacting the success to get it in series. All these combustion process designs aim on homogenization (no stratefication if possible) and the highest possible combustion efficiency in low load and therefore cycle relevant operation points. To achieve this you don't need squish, as this increases the CO in low load and the NOx in higher loads (RDE relevant).
DAMPFHAMMER engine:
2000 ccm, Honda K20 NA engine
4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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Re: Does quench affect power?

Post by LotusElise »

David Redszus wrote: Tue Sep 20, 2022 9:20 pm When dealing with matters of great complexity, it is normal to simplify to assist understanding.
But that comes with a substantial loss of accurcy and often even with misdirection.
Yeap, simulation need confirmation of the test bench results. But to shape that picture a bit more. What I've saw in 3D-CFD simulations, 1D-simulations and test bench on several engines was quite good correlating regarding combustion duration, heat release curve shape in quality and somewhat in quantity as well as knock behavior. And that is what it is all about once it come to performance.

I am not saying this is all time the case, but it can be when models get sharpened on measurement data. We used full sized pressure induced intake, cylinder and exhaust on various single cylinder, V8 and V12 engines for that and many other purposes.

What I've learned from that experience was I always invest on simulation approaches in a two step way, 1st on a very abstract one, e.g. check of physics parameter bandwidth to see what should be plausible and maybe at a more detailed to get a tighter range and 2nd with an abstract model of the situation. The more detailed, the more risk to be wrong or right :wink:. A simple single look at one situation is always too risky in case of design studies based on no predecessor verification. Experience helps a lot, so standing on the test bench and revise theory is duty for designers.
DAMPFHAMMER engine:
2000 ccm, Honda K20 NA engine
4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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Re: Does quench affect power?

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skinny z wrote: Tue Sep 20, 2022 9:38 pm A friend of mine wrote his mechanical engineering thesis on the internal combustion engine.
In it, as published, was stated that the best combustion chamber was a sphere with it's ignition source in the centre.
I guess around the 70'ies or 80'ies. What was the purpose of his master thesis?

You may know the book by Author Ludwig Apfelbeck "Wege zum Hochleistungs-Viertaktmotor", he was one of the guys using spherical heads for high output engines for BMW in the 70-80'ies, but it was Paul Rosche, using the first roof chamber head at BMW for the legendary M12 1.5 liter up to 1500 hp engine, driven by Piquet and Berger. Just last week I measured and parameterized an original connecting rod of this M12 engine, which is an amazing peace of engineering.

I know by far not all engines in essential racing series in Europe, but spherical heads are very rarely used in the late 90'ies till today. Hemi-heads are much more popular in the US, maybe they survived longer there. What I know is that flat head, wedged heads and roof chamber heads are used today in the V8 market. Are there spherical heads still there? Maybe the V2 engine of Harley-Davidson?
DAMPFHAMMER engine:
2000 ccm, Honda K20 NA engine
4000 rpm bandwidth of at least 192 ftlb
310 hp@8200 rpm
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Re: Does quench affect power?

Post by skinny z »

LotusElise wrote: Wed Sep 21, 2022 4:42 am
skinny z wrote: Tue Sep 20, 2022 9:38 pm A friend of mine wrote his mechanical engineering thesis on the internal combustion engine.
In it, as published, was stated that the best combustion chamber was a sphere with it's ignition source in the centre.
I guess around the 70'ies or 80'ies. What was the purpose of his master thesis?

Are there spherical heads still there? Maybe the V2 engine of Harley-Davidson?
Yes. That would have been in the early 80's.
As for the point of the thesis, 1) It was a matter of mutual interest and 2) He wanted to graduate!
Regarding spherical chambers in use today? That I can't answer. My focus (and only focus really) is in the small block Chevrolet cylinder head originally designed in the 50's and survives and thrives to this day.
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Re: Does quench affect power?

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David Redszus wrote: Tue Sep 20, 2022 9:20 pm Even without a clearly defined squish pad (as in a hemi), piston motion still creates significant charge motion. As the piston moves upward on the compression stroke, it scrapes the air (and fuel) from the cylinder wall. Where does this air go and at what velocity? All the squish calculations (including mine) are actually approximations which do not reflect true closed cycle turbulence, either BTC or ATC. And the actual squish induced turbulence is always engine specific reflecting chamber and piston dome. When dealing with matters of great complexity, it is normal to simplify to assist understanding. But that comes with a substantial loss of accurcy and often even with misdirection.
I agree that all of these "tumble" and "squish" words are just mental models that are gross simplifications of what is actually going on inside the engine. I also agree that at the same time they are very useful models, especially in thinking about what obviously won't work and to organize past experience about what has worked. I am firmly in the camp that thinks that simple summary statistics and concepts are very useful.

Perhaps we should relate these "squish", "swirl", and "tumble" ideas to two potentially more fundamental concepts related to what you wrote.

There's the one idea of how to preserve the intake flow as very large eddies as long as possible such that it doesn't dissipate as heat before the combustion. I would put the two-valve "swirl" and four-valve "tumble" into these categories.

There's the second idea of how to use the piston to do work to increase the total kinetic energy before and during the combustion. I would call that "squish".

Of course this is also an incomplete model because just a very small amount of "squish" can be used to time the break-up of "tumble" to smaller turbulent eddies at the exactly right time to create a very consistent combustion. So it's not like the two concepts are independent.

Do you think that is a helpful way to think about the issue?
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Re: Does quench affect power?

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David Redszus wrote: Tue Sep 20, 2022 9:20 pm When dealing with matters of great complexity, it is normal to simplify to assist understanding.
But that comes with a substantial loss of accurcy and often even with misdirection.
You hit a bunch of nails on the head with that statement. Nowhere is this more prominent than in lubricants. Those oversimplified drawings of different sized "balls" comparing different base oils drives me nuts.

Anyway, sorry... carry on.
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Re: Does quench affect power?

Post by hoffman900 »

From Randy Gillis (formerly of JE Pistons, now at Racetec. Also ‘piston_guy’ on here):
I did the first "tapered" or conical dish pistons for (then) Busch series engine builder Frank Leeson of Bill Davis Racing . He approached me with the idea and we made some test parts for him. Several dimensions were changed and those changes had a very clear affect on performance. One critical aspect was the width of the "perimeter squish band". Frank and I morphed the piston into the "spherical radius" from the conical due to the need for increased negative volume. After a couple of weeks I was contacted by Bob Fisher ( then of Ernie Elliott Inc) who was building engines for Bill. I gave both of them a 1 year exclusive on the design and development. Both did extensive back to back ( spherical to mirror image dish) testing . The spherical required at least two degrees less timing and always made a significant improvement to torque with a smaller improvement in HP. We figured combustion efficiency was responsible for that. There was also a stability condition. the feeling was the load was focused in the center and not offset by the mirror image dish. After the year was up , I offered the design to a west coast Craftsman truck ( then) engine builder. He was extremely skeptical and wanted no part of this "dumb design". I offered to ( and did) make two sets of equal pistons weight , rings, skirt profile, dish volume , etc . except for the dish design. The deal was to test the "conventional" design he was using first and then ( while still on the dyno)) pull it down , change the pistons and use the same used rings , and test it again. The result was a 10 hp 13 ft lb increase in power with 2*s less timing required. We didn't "invent" the concept , it was already out there on Hondas and other imports, we just adapted it to the V8 engine. There would eventually be a few cases where results were neutral as far as power increase but we did the design on all kinds of pistons. None made LESS power. I still use it today

Warp speed should remember when the concept hit and how soon it became available from every piston supplier. He might even have some comments on it.
Bryan Maloney wrote: Sat Sep 18, 2021 11:20 pm We had swirl, tumble, and wet flow test equipment available as part of Dodge's Nascar effort from 2000 to 2012.
We measured swirl as rotational torque with a honeycomb insert and a rotary strain gauge. Tumble was measured on another fixture with a perforated plate and three load cells. Data from the three load cells gave us total combined tumble torque, and more importantly, the force location defined as distance from the bore center and clocking in degrees.
We found that the swirl and tumble combined define the helix of the incoming air column in a two-valve chamber.
As Mummert stated, the swirl tends to jump up at low lift, lag behind in the mid-lift, and ramp up again at high lift. The tumble curve tends to do the same. The tumble force location (we called it "moment arm") moved closer to the bore center as the intake valve opened, and moved away from the bore center rapidly at high lift, when the swirl was spiking.
Our conclusion was we needed a smooth, linear increase in the swirl as the valve opened; not a set value.
To manage the swirl, we worked with chamber containment of the flow cone, runner trajectory, and some slight steering with the fin behind the guide. The flow must stay attached to the short-turn; swirl and tumble go out of control if there is separation. The modern steep seat and top angles really helped.
Reverse swirl fins behind the intake guides can improve burn uniformity, BSFC, and help prevent the swirl from spiking at high lift.
If you can do some wet flow testing on your cylinder head, you will be mesmerized by what you see. It will tie in with your swirl and tumble observations.
Bryan Maloney wrote: Sun Sep 19, 2021 3:53 pm
maxracesoftware wrote: Sun Sep 19, 2021 2:50 pm on a Chrysler ProStock Truck , Bowl Swirl Fin gains 15+ CFM @ 28" on Flowbench ,
absolutely no ET or MPH gains , no difference down Dragstrip ,
so that without Swirl Fin you loose 15 CFM , but runs eaxctly the same as Bowl Swirl Fin that gains 15+ CFM on Bench.
Basically , a Bowl Swirl Fin ends up as Flow Numbers "Bragging Rights" , but no HP or ET performance gains !
I observed almost the same thing years ago after adding reverse swirl fins to a pair of 18 degree Chevy heads on an open ARCA engine. Picked up 8-13 cfm on the bench, but no power increase on the Dyno.

Mike Chapman added the reverse swirl fins to a set of 18 degree heads for one of our Cup restrictor plate engines back in the 425hp/7000 rpm era. They were 2-3 hp better than the non-finned plate heads we received from him. The piston and chamber coloring looked phenomenal after racing them.

With the Dodge program, we ended up putting our effort into optimizing the tumble characteristics over the swirl.
Bryan Maloney wrote: Tue Sep 21, 2021 9:37 am
hysteric wrote: Sun Sep 19, 2021 4:38 pm
Bryan Maloney wrote: Sun Sep 19, 2021 2:43 pm

No, our goal was to prevent the swirl from ramping up so highly at high lift. When the goal is cylinder filling, we wanted the air column helix to chase the piston down the bore and not sling the fuel into the cylinder walls.
Street engines with low valve lift may benefit at low RPM from additional swirl; the valve L/D never gets high enough to where the swirl naturally spikes.
The often maligned reverse-swirl "Elkins fin" behind the intake guides can be beneficial in moderation. Some OEM's take this feature to the extreme.
A "Glidden fin" along the centerline of the floor of the intake port can add flow stability and help limit high lift swirl.
Thanks Bryan, did you experiment with different droplet sizes? Also at what L/D's was it evident that spiking occurred?
We did not vary droplet size. The fluid was a mist leaving the booster. The swirl ramped up after .500 lift using a 2.170 valve.

Note in the photo there are two vortices in the chamber; one above and to the left of the intake valve and one between the plug and the exhaust valve. Just as there can be tornadoes within a hurricane. Swirl testing rigs are only showing net swirl, wet flow shows the motion is much more complex.

This photo does not do justice to what you actually see in motion. Everyone that has seen this in action has been mesmerized.


Effect_20210921_091526.jpg
Photos from Bryan here: viewtopic.php?t=64060

F5838C11-71E5-4FCB-BAF6-3A2FEE26DE26.png



https://youtu.be/rBZCnG1HwDM (starting at 39:00)
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