Combustion chamber in the wrong spot??

[Red97]

So, back at these silly echo projects.
After boring welding boring welding grinding welding boring and finally sleeving a cylinder.
Just to bore it and hone it to size.

I end up with this...


Now it is hard to tell, but the flat band is about .300" wide then a 5* taper into what is left of the combustion chamber.

So I did this. Made this pop up, head the other direction.


Figured I need less comp and more volume.

Thoughts? Comments? Concerns?

Thanks.

 

[Mastermind]

Good idea. Also more surface area for the expanding gases to press upon.

 

[Lee H]

Sachs Dolmar did this years ago with a few models where the piston had a dish.
They claimed it put more pressure on the piston on the combustion stroke and
making more power.

 

[Eagle1899]

Like a diesel piston. If I'm thinking correctly, it should respond well to a timing advance. Combustion taking place in a smaller area.

 

[Eagle1899]

Smaller area is not the right word. Lower combustion chamber would be more accurate. Smaller dome with a dished piston effectively moves the chamber lower.

 

[Red97]

Good idea. Also more surface area for the expanding gases to press upon.

I knew the pop up was a no go right off, but curious to see the wash pattern? Can see the gasses staying in the dish, but not sure if that is a good or bad thing..

Sachs Dolmar did this years ago with a few models where the piston had a dish.
They claimed it put more pressure on the piston on the combustion stroke and
making more power.

Interesting, I was just hoping to get the compression down to a manageable number on this build. Back when it was still 54mm with a flat top, it had mega compression. May need an extra degree or 2 off the exhaust roof.

Smaller area is not the right word. Lower combustion chamber would be more accurate. Smaller dome with a dished piston effectively moves the chamber lower.

Curious as to how it will affect heat any, having most all of the "chamber" closer to the exhaust roof. Seems if the psi is manageable, it could almost run cooler. Doubt it is enough to notice though.

 

[Mastermind]

I knew the pop up was a no go right off, but curious to see the wash pattern? Can see the gasses staying in the dish, but not sure if that is a good or bad thing..

I don't pay much attention to wash patterns. The bottom line....how does it run?

We'll see.

 

[Nutball]

Would the increase in piston surface area put too much heat into it?

 

[AlexStromberg]

Like a diesel piston. If I'm thinking correctly, it should respond well to a timing advance. Combustion taking place in a smaller area.

Diesel pistons have way deeper pistons, called a bowl for a reason. The same principles wont work in a non DI engine.

 

[Bigmac]

I don’t have the calculator for it, but a maximum squish velocity would be interesting on that. A increase in squish could still yield more the correct velocity, at the correct compression. A dish will help compression, ideally I would like to see it match the squish band, otherwise it possible for detonation to occur.

 

[drf256]

Always wanted to do a dish, especially in 1122 Stihl and other models where dropping the jug to the wanted ex roof caused too much compression.

I was told the negative was that loop scavenging would not being able to clear the piston off. I can’t see that being true because the piston is in constant movement. The increased surface area will add heat to the slug, but no more than a pop up would.

I don’t buy the whole more surface area to push on. Pressure is pressure. No more force is added or obtained from a different in surface area.

Does the squish area on the piston match the squishband?

 

[Eagle1899]

@AlexStromberg that's correct.

Alot of diesel have no combustion chamber in the head. They are flat with the valves. The entire combustion chamber is in the piston.

 

[Nutball]

Always wanted to do a dish, especially in 1122 Stihl and other models where dropping the jug to the wanted ex roof caused too much compression.

I was told the negative was that loop scavenging would not being able to clear the piston off. I can’t see that being true because the piston is in constant movement. The increased surface area will add heat to the slug, but no more than a pop up would.

I don’t buy the whole more surface area to push on. Pressure is pressure. No more force is added or obtained from a different in surface area.

Does the squish area on the piston match the squishband?

Pressure is pressure, it's the straight down force vector we care about. But could the side vector of the gas on a sloped surface of the piston have a ramp effect at least helping increase the piston speed possible from the same rate of gas expansion if not also add to the downward force?

 

[Loony661]

I would just break the edge in the combustion chamber - sharp edges create a detonation point because they get/stay hotter, acting as an ignition source.

 

[redline4]

Just for reference, this piston is from a GM direct injected 1.5L gas turbocharged engine.


Plenty of edges and ridges on it. The dished portion is where the fuel injector nozzle directs the fuel, straight into the dish.

 

[Red97]

Well it runs and has a touch less comp than thr 54mm version with a flat band.

 

[Red97]

Always wanted to do a dish, especially in 1122 Stihl and other models where dropping the jug to the wanted ex roof caused too much compression.

I was told the negative was that loop scavenging would not being able to clear the piston off. I can’t see that being true because the piston is in constant movement. The increased surface area will add heat to the slug, but no more than a pop up would.

I don’t buy the whole more surface area to push on. Pressure is pressure. No more force is added or obtained from a different in surface area.

Does the squish area on the piston match the squishband?

The flat part of the squishband is just a bit smaller than the flat of thr piston crown. Ended up thst way so I could blend the taper in.

 

[Red97]

Well.... it was still running....

 

[cus_deluxe]

Not bad for the amount of times that got hot lol.

 

[Nutball]

Were you running Dominator?