# 3D Printed Piston | Lower mass = Power

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novaguy
What is said there is about lowering friction force, and vibrations which can all lead to more power. You already mentioned the friction in the OP:
You conveniently left out the conclusion by the NREL study showing piston mass to increase MEP.

"A study by the National Renewable Energy Laboratory (NREL) found that reducing the mass of the pistons in a spark-ignition engine improved the engine's thermal efficiency by up to 3%. This was attributed to the reduction in the reciprocating inertia of the pistons, which in turn allowed for a more rapid acceleration of the engine and an improvement in the mean effective pressure."

The study results make sense if you don't overthink it.

Work done at a faster rate equals more power.

Work can be done faster with lighter reciprocating components.

There aren't some magical parasitic forces that increase to counteract all the increased work that becomes available; some of it goes to engine output.
novaguy said:
will this lighter piston result in a small power increase as less work done by reciprocating the piston
There are at least 4 studies that say yes.

@novaguy
A simple statement, without any specified conditions, may appear to be true in one specific case, but that does not make the simple statement unconditionally true in the general case.

The more you cherry-pick to make your original belief seem correct, the more opposition you will receive from others, who must refuse your unconditional general statements.

russ_watters and berkeman
novaguy
The more you cherry-pick to make your original belief seem correct, the more opposition you will receive from others, who must refuse your unconditional general statements.
I don't think I cherry picked anything. So far, there is mostly conjecture on whether or not reciprocating inertia increases power. Just people stating off the top of their heads what they think.

What I've found though various studies and my own data is that lower piston mass does increase power. Whether through reduced friction due to mass, lower bearing loads, and or less reciprocating inertia.

I used basic dynamics equations to compare identical engines with 2 different piston masses, posted earlier. There is a clear increase in the rate that torque is generated due to lower reciprocating inertia. It allows the work to be done faster by the combustion gas expansion. The energy is produced faster and given back to the rotating components faster.

I figured it would be easy for someone to confirm or refute these claims with a few equations. I understand not everyone wants to take their time to explain it

Where the work is done for only part of the cycle, are you referring to only the part of the cycle where work is being done, the work per full cycle, or the work done over a full working day.

Work done at a faster rate equals more power.

Work can be done faster with lighter reciprocating components.
Under what conditions do you believe those general statements to be true?

Piston failure must be avoided, because it destroys the investment in the engine. Lighter pistons tend to be more fragile and less durable. It only takes one unusual situation to destroy a poorly designed piston. Before designing and prototyping a piston, you need to examine a collection of failed pistons, then examine your new design in the light of all the failure modes that may be encountered in normal operation.

Piston engines are an old technology.
There are more economic solutions that deserve more urgent attention.

Gold Member
"A study by the National Renewable Energy Laboratory (NREL) found that reducing the mass of the pistons in a spark-ignition engine improved the engine's thermal efficiency by up to 3%. This was attributed to the reduction in the reciprocating inertia of the pistons, which in turn allowed for a more rapid acceleration of the engine and an improvement in the mean effective pressure."
You do understand that these words were assembled together by a Chatbot that surely hasn't reviewed a study (if it exists) and then share its conclusions with you?

You should find that study because nobody will argue with a Chatbot.

For my part, I think you have enough comments - from so many people - that have answered your question all the same way. On eng-tips.com you do seem to have a friend with SwinnyGG, but in the end, he's saying what I already told you:

Reducing mass may reduce the normal forces between the components, leading to fewer friction losses. That is the only way you can explore the higher efficiency of your engine.

russ_watters and berkeman
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