So, Why Oval?

[PureHybrid]

I'm not sure at what point they are spraying fuel in the DI gas engines, but I assume it's far enough before spark occurs that it doesn't matter.

 

[Mike]

I have dealt with Greg and I have dealt with Fingers. Fingers is by far the man when it comes to cylinder knowledge. I still use his cylinder pressure monitor, to this day. How many years has that been, Jon? He doesn't do or build anything half ass.

 

[Mike]

Tbt

 

[clrussell]

I'm not sure at what point they are spraying fuel in the DI gas engines, but I assume it's far enough before spark occurs that it doesn't matter.

I've actually heard they are turning off spark on gas DI engines at some points


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[TheBac]

We have ran a diesel engine at work with flat pistons and bowls in the head..

hey wait a minute don't you work at GM? so GM was testing this out?

Not on a duramax.

So GM is reviving the 5.7 Olds diesel?

 

[jlawles2]

If piston bowls are a bad thing, then why did the piston sitting on the desk at the engine shop that did my heads have one out of a JD harvester that had the bowl off to one side?? And it was crowned in the bottom. Piston was from an engine that ran 17 hrs in the field with no air cleaner and ate the pistons from the dust.

 

[Fingers]

Wow. Those are all interesting ideas on why the chamber is in the piston.

The main reasons that the modern diesel has the chamber in the piston are:

• To contain the air charge in as compact a space as possible with the least surface area. Ideally, it would be a sphere, but round works. Ovals, it turns out, are actually two nearly spherical chambers interconnected. The bump is the middle of a round or oval chamber is because there is essentially no fuel available to burn there because of the injector pattern and it ends up being dead space.
• Related to the first. The piston chamber helps reduce quench. This is where the surrounding metal absorbs the heat of the charge to the point that it puts the fire out. Compared to the head and cylinder walls, the piston is almost always "Hot". So the more you put the chamber in the piston, the more heat that will stay in the air charge. Compared to the stock bowl, the ovals have less piston area and more head exposure. The result can be some cold chamber hazing.
• To help reduce the fuel splatter onto the cylinder walls. This is important for a lot of reasons. Fuel on the cylinder wall will not vaporize, (too cold) and will displace any lubrication on the walls from the oil.

Flow in any flat head design is compromised because of the required vertical valve positioning.

 

[PACougar]

Thanks for the explanation Jon.

 

[hntngkd]

So GM is reviving the 5.7 Olds diesel?

Sure we'll go with that. lol

 

[S Phinney]

Wow. Those are all interesting ideas on why the chamber is in the piston.

The main reasons that the modern diesel has the chamber in the piston are:

• To contain the air charge in as compact a space as possible with the least surface area. Ideally, it would be a sphere, but round works. Ovals, it turns out, are actually two nearly spherical chambers interconnected. The bump is the middle of a round or oval chamber is because there is essentially no fuel available to burn there because of the injector pattern and it ends up being dead space.
• Related to the first. The piston chamber helps reduce quench. This is where the surrounding metal absorbs the heat of the charge to the point that it puts the fire out. Compared to the head and cylinder walls, the piston is almost always "Hot". So the more you put the chamber in the piston, the more heat that will stay in the air charge. Compared to the stock bowl, the ovals have less piston area and more head exposure. The result can be some cold chamber hazing.
• To help reduce the fuel splatter onto the cylinder walls. This is important for a lot of reasons. Fuel on the cylinder wall will not vaporize, (too cold) and will displace any lubrication on the walls from the oil.

Flow in any flat head design is compromised because of the required vertical valve positioning.

Exactly Jon! I'm just not as good with the words as you.

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[Hot COCOAL]

Hey Jon, that was awesome man, thanks for taking the time to type that..
I have a question about "quench" I was hoping you, or someone could address for me

I thought that "quench" was just a term for (not even sure if I can explain my thought adequately) the volume required to contain the combustion event, while also being the proper point for to create the most energy transfer?

So that's totally wrong...lol
I know, I'm not too bright, cuz now that I think about it, to quench something is to extinguish, smother or snuff out...hgeez:


Now as I understand how you explained it...the quench point IS the point that extinguishes the flame? Is that all that the term "quench point" envelopes?

 

[Stingpuller]

Pretty funny about boy wonder

I think its pretty simple they seem to work and work well for what they are intended to do. I also like forged pistons in a race motor but the Fingers piston seem to be holding their own. In a street performance motor I would say there the top dog. Hard to argue with facts.

 

[ikeG]

I think its pretty simple they seem to work and work well for what they are intended to do. I also like forged pistons in a race motor but the Fingers piston seem to be holding their own. In a street performance motor I would say there the top dog. Hard to argue with facts.

Forged fingers:thumb:

 

[malibu795]

Hey Jon, that was awesome man, thanks for taking the time to type that..
I have a question about "quench" I was hoping you, or someone could address for me

I thought that "quench" was just a term for (not even sure if I can explain my thought adequately) the volume required to contain the combustion event, while also being the proper point for to create the most energy transfer?

So that's totally wrong...lol
I know, I'm not too bright, cuz now that I think about it, to quench something is to extinguish, smother or snuff out...hgeez:


Now as I understand how you explained it...the quench point IS the point that extinguishes the flame? Is that all that the term "quench point" envelopes?

Quench is normally when talking about engines reffered to the distance between piston crown and head deck surface. Why its called that IDK

Less quench the more air is shoved into the bowl/combustion chamber.
Only down side. Get too close you risk contact between piston/valves/head

Less quench is better... The LBZ in my red dually(had about 275-300hp) I went from B gaskets to C gaskets back to BS. The MPG and MPH in hills while loaded where noticeablly less with C gaskets I lost avg of 1mpg and 10mph pulling known grades at similar weights with nothing else changed. Put Bs back in I was back to previous MPG and speeds

 

[lil bleur]

I can't say why JD has the bowl off to the side, but that engine was most likely mechanically injected. John Deere's Piston and engine designs didn't change much between 1961 and 2007. The Injectors were angled into the head sort of like a 12v.

If piston bowls are a bad thing, then why did the piston sitting on the desk at the engine shop that did my heads have one out of a JD harvester that had the bowl off to one side?? And it was crowned in the bottom. Piston was from an engine that ran 17 hrs in the field with no air cleaner and ate the pistons from the dust.

 

[THEFERMANATOR]

I can't say why JD has the bowl off to the side, but that engine was most likely mechanically injected. John Deere's Piston and engine designs didn't change much between 1961 and 2007. The Injectors were angled into the head sort of like a 12v.

The offset bowl was due to injector placement from a 2 valve head. With 2valves per cylinder, the injector has to come in to the side of center, and you want the bowl centered under the injector, so offset bowl.

 

[Fingers]

My best guess on quench is that anything less than a 0.070" will snuff the flame. Once you get that close, you want to stay as small as possible without hitting.

 

[Fingers]

I think its pretty simple they seem to work and work well for what they are intended to do. I also like forged pistons in a race motor but the Fingers piston seem to be holding their own. In a street performance motor I would say there the top dog. Hard to argue with facts.

Oval bowls are also available in forged and are running is several race applications.

However, the cast ovals have raised the bar so the street rodder can have the advantages of a keystone ringed piston and handle significant power.

 

[Stingpuller]

Pistons

I just don't like the 2618 material for a race motor.

 

[56taskforce]

This makes for some very interesting reading. John the way I understand it is the oval is less efficient but a trade off we are willing to make for increased strength. Is this correct???