Piston Bowls

Fingers

Fingers

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This is a spin off from another thread.

I am nearly done with my piston bowl design and hope to cut the first one this weekend. I have used a FEA program to try and refine what I think is a reasonable compromise that does not require a significant reduction in compression ratio.

For background, here is the analysis of a stock LLY piston showing where the stress exceeds the strength of the material.

attachment.php


And here is a delipped piston under the same load. Note that it is NOT stronger than the stock piston.

attachment.php


Here is my latest design:

attachment.php


This maintains the stock compression ratio leaving some room for valve relief cuts if need be.

IF the FEA can me trusted, the design is 50% stronger than the stock configuration.

The cast pistons have a steel band embedded in them which I need to miss for the new design. So wish me luck when I cut the first one since I don't know exactly where it is on the blanks I have bought for this project.
 
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Leadfoot

Leadfoot

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I understand from a strength standpoint and failure analysis of where other pistons crack (along the wrist pin), that this will/should be substantially stronger, but what effect does an oval combustion chamber have on combustion? I know the injector leaves a "star" pattern on the top of the piston, and it would look like it would be contained in the bowl on the wide part of the oval, but end up on top of the piston where it is narrow (along the wrist pin). Does having the injector spray on top of the piston or the "lip" where it transitions have any ill effects? Or is the tradeoff not that significant (compared to keeping the piston together)?

Not doubting and VERY glad someone is trying new ways to keep the pistons from cracking (which is my main concern with my LBZ), just curious as usual.

Thanks Jon for trying this and reporting your findings.

Edit: Also you mention the steel band (I'm assuming for the Keystone ring), is there any danger (even if you don't hit it), that there would now be not enough material above it to wick away heat or cause the material in that area of the top of the piston to be too thin and become brittle or flake? Is the metal band part of your FEA or is it based off the entire piston being made of one material? Either way, I hope this turns out positive for you and for us....
 
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SmokeShow

SmokeShow

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Nov 30, 2006
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And you ARE going to be running injectors with OE spray pattern, right? I'm curious to see if you'll be able to see any effects of the mismatched pattern to bowl design with your cyl pressure gauge logs! Very interesting approach...

have any other engines ever had an odd shaped bowl in the piston?? I know there has been some irregular shaped combustion chambers within the heads before but don't recall having ever seen such a creature in a piston.

Too cool IMO. :thumb: :cool2:
 
TrentNell

TrentNell

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Pretty Cool stuff , look forward to your results , I really dont think the oval shape will hurt combustion , just look at a bowl after deliping and cutting valve reliefs , you can tell me the fuel is staying in the bowl well still after that , but i think if the "quench" is kept tight it should force the fuel in the bowl regardless of shape and combust properly.
 
Fingers

Fingers

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Leadfoot said:
I understand from a strength standpoint and failure analysis of where other pistons crack (along the wrist pin), that this will/should be substantially stronger, but what effect does an oval combustion chamber have on combustion? I know the injector leaves a "star" pattern on the top of the piston, and it would look like it would be contained in the bowl on the wide part of the oval, but end up on top of the piston where it is narrow (along the wrist pin). Does having the injector spray on top of the piston or the "lip" where it transitions have any ill effects? Or is the tradeoff not that significant (compared to keeping the piston together)?

Not doubting and VERY glad someone is trying new ways to keep the pistons from cracking (which is my main concern with my LBZ), just curious as usual.

Thanks Jon for trying this and reporting your findings.

Edit: Also you mention the steel band (I'm assuming for the Keystone ring), is there any danger (even if you don't hit it), that there would now be not enough material above it to wick away heat or cause the material in that area of the top of the piston to be too thin and become brittle or flake? Is the metal band part of your FEA or is it based off the entire piston being made of one material? Either way, I hope this turns out positive for you and for us....
Click to expand...


I am not sure about the spray pattern and its behavior with the oval. However, the "Finger" bowl's minor axis is as wide as the stock bowl. So no more, or less, fuel will spill over the top than the stock bowl. At least that is the theory. :)

In addition to the Keystone ring steel, there is an additional ring embedded in the piston. I know from cutting other stock pistons apart. It just so happens that I don't have any old pistons, whole or sliced, still laying around. IIRC it was just inboard of the oil gallery.
 
bullfrogjohnson

bullfrogjohnson

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Nov 20, 2006
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Fingers said:
I am not sure about the spray pattern and its behavior with the oval. However, the "Finger" bowl's minor axis is as wide as the stock bowl. So no more, or less, fuel will spill over the top than the stock bowl. At least that is the theory. :)

In addition to the Keystone ring steel, there is an additional ring embedded in the piston. I know from cutting other stock pistons apart. It just so happens that I don't have any old pistons, whole or sliced, still laying around. IIRC it was just inboard of the oil gallery.
Click to expand...

Lucky for you, the second ring is about 1" deep from the piston crown and around 7/8" in from the outside edge of the ring grooves.
IMG_20110107_194342.jpg

IMG_20110107_194416.jpg
 
dmaxfireman

dmaxfireman

'Can do' kind of guy
Apr 8, 2007
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very cool jon! i say that you said the compression ratio will be close to stock. is that lb7/lly or lbz stock?

i've always been interested in testing a higher compression piston
 
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