Piston Bowls

[juddski88]

What does this mean for valve reliefs? Better or worse for the piston? you say "quench gets in the way" but isn't it quench that helps create torque?

on edit:

by creating torque I mean: my understanding of quench is it that the tighter the quench, more pressure occurs inside the bowl and not outside of it. However, it sounds as if this is not best? Am I understanding that properly?

 

[Fingers]

Just to understand this in a simplier term. Basically the pressure difference between the cylinder and piston vs the the pressure in the piston bowl is a big problem? And that is what is hurting them the most? If so than it would seem delipping is a must to help with it? Because I have seen a few people who don't believe delipping helps.

Sent from my PC36100 using Tapatalk

Honestly, I am not sure. The dynamics of the pressure flow from ignition are complicated. I do not think delipping is significant in that regard.

I tend to think, however, that the area around the piston is primarily pumped up by the compression stroke near TDC when peak chamber pressures are seen. I'm not sure if valve reliefs help or hurt. If all the turbulent chamber models are to be considered. The quench area has a much higher pressure than the central chamber and would also greatly increase the pressure around the piston. IF that is the case, then valve reliefs would reduce the pressure.

 

[JoshH]

Do you have any ideas what causes the pressure to not equalize between the piston bowl and the pressure between the piston and cylinder wall? Would you say running less protrusion and/or more piston to cylinder wall clearance would help? Anything you could do with tuning to help?

 

[LWATSON]

What would happen if the pistons were machined so the top wasn't flat but angled down on a sloap from the outer edge to the bowl just a few degrees? Would this lower compression too much? Just wondering if this would help keep the force off the outer portion of the piston?

 

[Leadfoot]

Honestly, I am not sure. The dynamics of the pressure flow from ignition are complicated. I do not think delipping is significant in that regard.

I tend to think, however, that the area around the piston is primarily pumped up by the compression stroke near TDC when peak chamber pressures are seen. I'm not sure if valve reliefs help or hurt. If all the turbulent chamber models are to be considered. The quench area has a much higher pressure than the central chamber and would also greatly increase the pressure around the piston. IF that is the case, then valve reliefs would reduce the pressure.

What you say seems to back real world testing/results.

Toroidal (OEM emissions bowl) pistons would seem to have the worst pressure differences (fluid dynamics and pressure equalization) as air/fluid is trapped in the bowl and has a tougher time equalizing to the rest of the cylinder. Would make sense why delipped pistons "tend to be stronger" even though material is removed. I would think valve reliefs would help as well (unless a hot spot is created in doing so) as it would allow a path for pressure to equalize.

It seems from a strength standpoint a dished piston would be the best for strength but probably not work well for emissions or efficiency. A comprimise has to be made, it's just finding the best middle ground (and your pistons seem to be a good start).

 

[Fingers]

What would happen if the pistons were machined so the top wasn't flat but angled down on a sloap from the outer edge to the bowl just a few degrees? Would this lower compression too much? Just wondering if this would help keep the force off the outer portion of the piston?

Thin areas do not burn fuel well if at all. flame fronts that enter these areas tend to get snuffed out. Thus the term "quench" area for the top of the piston. I would think a slope towards the bowl would promote quench.

Sloped the other way sounds interesting though.

 

[Fingers]

What you say seems to back real world testing/results.

Toroidal (OEM emissions bowl) pistons would seem to have the worst pressure differences (fluid dynamics and pressure equalization) as air/fluid is trapped in the bowl and has a tougher time equalizing to the rest of the cylinder. Would make sense why delipped pistons "tend to be stronger" even though material is removed. I would think valve reliefs would help as well (unless a hot spot is created in doing so) as it would allow a path for pressure to equalize.

It seems from a strength standpoint a dished piston would be the best for strength but probably not work well for emissions or efficiency. A comprimise has to be made, it's just finding the best middle ground (and your pistons seem to be a good start).

The more material you take from over the pins, the weaker they get. Additionally the thinner the chamber section, the less efficient the burn. You have to remember that only the boundary of the fuel plume burns. So the more edge, the better. There needs to be a balance or compromise somewhere.

I have tried to keep the chamber(s) fat while increasing the material over the pins. The result is an elliptical chamber that actually ends up being two chambers.

 

[minisub]

You've now been cross-linked on CompD, post 25:

Billet Rods for the DMAX Thread

 

[cafryer]

The completed stand. Sooooo much more substantial than the old stand. no bounce at all.

I have another mounting plate that I think I will make into another hanger for the old stand. Maybe something simpler. I've noticed that the left and right side of the motor have some hole that match up. One plate fits all? Maybe a combo plate.


One thing I like about the side hanger is you can install the cam vertically. Especially nice on these engines.

Will this hold the weight of a fully dressed engine being it only mounts to one side.

 

[Fingers]

It held mine fine.

 

[WolfLMM]

Bingo!

I have my engine tore down right now, seriously considering upgrading the hard parts in this puppy. Have you made any changes to the model since I posted a program? I have figured out more stuff on surfcam, no more 30 minute crappy programs.

Did you ever buy a seat?

Over 10,000 miles on my set of pistons now. No issues. My transmission, however, is not so happy.

Something that was bothering me about the FEA was that it showed these, and the stock and the others piston designs failing at lower pressures than I have seen and measured in the real world. I couldn't understand how they were surviving at all. So I used the analysis tool just as a comparative widget so I could see what was better.

Then I stumbled on the issue in my analysis. I was not applying the pressure to the area on the outside of the piston above the fire ring. This turns out to be critical to the piston's strength assessment and, I think, piston longevity in the real world.

Cutting to the chase, this means the pressure differential between the center of the piston and space between the piston head and cylinder wall is THE factor that kills the pistons mechanically. That differential happens when the ignition event is very fast such that pressure does not have a chance to equalize between the center of the piston and the cylinder wall area or when the path is restrictive, like at top dead center when all that quench area is in the way.

 

[WolfLMM]

Just to understand this in a simplier term. Basically the pressure difference between the cylinder and piston vs the the pressure in the piston bowl is a big problem? And that is what is hurting them the most? If so than it would seem delipping is a must to help with it? Because I have seen a few people who don't believe delipping helps.

Sent from my PC36100 using Tapatalk

Problem is, when you delip, you remove material crucial to the strength of the piston. I don't see the lip inhibiting flow that much, as to make a huge difference in pressure differential.

 

[Springer415]

sub

 

[Fingers]

Bingo!

I have my engine tore down right now, seriously considering upgrading the hard parts in this puppy. Have you made any changes to the model since I posted a program? I have figured out more stuff on surfcam, no more 30 minute crappy programs.

Did you ever buy a seat?

The basic bowl is the same. I have made changes to accommodate the various compression ratios. I also have a beta that improves the machine paths using shape primitives that the CAM software(s) understand. Hope to cut the next set with those.

Chip time is about 20-25 min for each piston depending if the piston has valve reliefs. The aluminum on these pistons is very abrasive if you push the carbide to fast.

I bought a Solidworks seat as well as a 3D CAMworks seat. CAMworks is integrated into Solidworks so I don't have to switch back and forth between programs and deal with file conversions.

 

[WolfLMM]

Surfcam works the same way. No conversions. I would like to cut a set for my truck. Got to find time first.

Keep us updated,

Wolf

 

[JRODS*LB7]

would this work? feel free to laugh at my drawing....lol

 

[Fingers]

Surfcam works the same way. No conversions. I would like to cut a set for my truck. Got to find time first.

Keep us updated,

Wolf

Well, Surfcam did not when I was test driving the products last year. It could read Solidworks files, and you could run it from within Solidworks, but it was not native to Solidworks.

CAMworks stores the CAM data in the Solidworks file itself. The posts are generated from that same Solidworks file. It looks like Surfcam has come around to a similar offering.

There are other differences, but it is more of a preference thing.

 

[Fingers]

would this work? feel free to laugh at my drawing....lol

Not sure what you are trying to get across there partner.

 

[jmaz268]

Not sure what you are trying to get across there partner.

Think he means by the way the bowl is shaped as if it would work.

 

[JRODS*LB7]

this reply

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....

thats why i came up with the crappy drawing design