Reciprocating weight tests ?

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SchmidtMotorWorks
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Re: Reciprocating weight tests ?

Post by SchmidtMotorWorks »

Stan Weiss wrote: Wed Mar 08, 2023 2:48 pm Hi Geoff,
This is the only article that I could find.

Rear Wheel Power Increases - The Spin Zone
Here are eight ways to get big rear-wheel POWER INCREASES without having your ENGINE make one hp more.
David Vizard photographer Johnny Hunkins photographer
Dec 12, 2006
https://www.motortrend.com/how-to/0602p ... -increase/

cheers,
Stan
I'm curious, who believes that reducing rotating mass increases power?
Also, who thinks that dyno or track testing is a good way to find the answer to that question?
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Re: Reciprocating weight tests ?

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SchmidtMotorWorks wrote: Thu Mar 09, 2023 2:03 am A lot of people make the intuitive mistake of imagining that reciprocating mass consumes energy to accelerating the mass each time it reverses without recognising that the energy is recovered when the mass decelerates.

Low mass rotating and reciprocating parts (both) require less energy to accelerate from a given rpm to a higher rpm.

At steady state operation, the low reciprocating mass reduces friction due to side loading.
At steady state operation, rotating mass doesn't have a significant impact on friction other than the trivial friction due to gravity loads on the bearings.

I hope that no one really did a dyno test to check that.
It was a big thing n the 90s to reduce reciprocating weight ( at least I thought it was) now it's a nothing, in fact light weight wrist pins are scorned ( although I think that started in the 90's) So curious why the change besides lighter won't cyclic stretch rod bolts as much and heavier can be strong enough to take the easy to make horsepower these days.
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Re: Reciprocating weight tests ?

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Tom68 wrote: Thu Mar 09, 2023 2:44 am
SchmidtMotorWorks wrote: Thu Mar 09, 2023 2:03 am A lot of people make the intuitive mistake of imagining that reciprocating mass consumes energy to accelerating the mass each time it reverses without recognising that the energy is recovered when the mass decelerates.

Low mass rotating and reciprocating parts (both) require less energy to accelerate from a given rpm to a higher rpm.

At steady state operation, the low reciprocating mass reduces friction due to side loading.
At steady state operation, rotating mass doesn't have a significant impact on friction other than the trivial friction due to gravity loads on the bearings.

I hope that no one really did a dyno test to check that.
It was a big thing n the 90s to reduce reciprocating weight ( at least I thought it was) now it's a nothing, in fact light weight wrist pins are scorned ( although I think that started in the 90's) So curious why the change besides lighter won't cyclic stretch rod bolts as much and heavier can be strong enough to take the easy to make horsepower these days.
I had a "heavy" and a "light" combo no really apples to apples, but one bent the crank while the other had the rod fly out. "Too high DCR" can feel like a loss of POWER if the system is not tuned to correct RPM... The parts better be light when its close because that doggone thing can hit like a brain buster! :D



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Re: Reciprocating weight tests ?

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Amount of mass change, location of mass change from center line, rate of acceleration of mass, rotation velocity of mass all are part of the calculations.

These were done about 6 1/2 years ago.

Stan
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Re: Reciprocating weight tests ?

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I'm curious, who believes that DVs claim that reducing mass increases rear wheel power?
Hint; The work being done was reduced, the power was not increased.

This can be computed more precisely than dyno or track testing can.
If dyno or track testing contradicts the computation, the testing is flawed.
Rear Wheel Power Increases - The Spin Zone
Here are eight ways to get big rear-wheel POWER INCREASES without having your ENGINE make one hp more.
David Vizard photographer Johnny Hunkins photographer
Dec 12, 2006
https://www.motortrend.com/how-to/0602p ... -increase/
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Re: Reciprocating weight tests ?

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SchmidtMotorWorks wrote: Thu Mar 09, 2023 11:02 am I'm curious, who believes that DVs claim that reducing mass increases rear wheel power?
Hint; The work being done was reduced, the power was not increased.

This can be computed more precisely than dyno or track testing can.
If dyno or track testing contradicts the computation, the testing is flawed.
Rear Wheel Power Increases - The Spin Zone
Here are eight ways to get big rear-wheel POWER INCREASES without having your ENGINE make one hp more.
David Vizard photographer Johnny Hunkins photographer
Dec 12, 2006
https://www.motortrend.com/how-to/0602p ... -increase/
I think it’s super beneficial for everyone to data log in car and record / calculate sweep rates. Ultimately that’s what matters.
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Re: Reciprocating weight tests ?

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hoffman900 wrote: Thu Mar 09, 2023 11:11 am I think it’s super beneficial for everyone to data log in car and record / calculate sweep rates. Ultimately that’s what matters.
Vehicle performance and engine power are two different questions.
The claim made by DV was that reducing mass increased power; that is false.

A change in car performance due to weight reduction is not indicative of a change in power.
It is indicative of a change in work being done.
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Re: Reciprocating weight tests ?

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SchmidtMotorWorks wrote: Thu Mar 09, 2023 11:19 am
hoffman900 wrote: Thu Mar 09, 2023 11:11 am I think it’s super beneficial for everyone to data log in car and record / calculate sweep rates. Ultimately that’s what matters.
Vehicle performance and engine power are two different questions.
The claim made by DV was that reducing mass increased power; that is false.

A change in car performance due to weight reduction is not indicative of a change in power.
It is indicative of a change in work being done.
Oh I agree, I’m just speaking from a 1000’ view on what others should be looking at.
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Re: Reciprocating weight tests ?

Post by David Redszus »

The topic of reciprocating (and/or rotating) mass and forces can easily develop into a very technical
discussion requiring some advanced math. Dyno testing is not sufficiently accurate to test the
changes in forces due to mass change and location change.

Every point along the rod length transcribes an ellipical orbit with crank rotation; almost
none of the rod motion is reciprocating. Yet, the mass distribution of the rod must be
considered, including polar moments and ellipical orbits.

Reciprocating forces can be calculated using stroke, rod length, rpm and piston
assembly mass. Calculating rotating forces are a real problem for the reasons
stated above.

The main objective of rod/piston mass analysis is to determine the design of the
crankshaft counterweights, not overall engine performance. What is on the table
is bearing loading, vibration and harmonics.
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Re: Reciprocating weight tests ?

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Given that a reasonably well balanced V8 can have so low of vibration (some of it originating from the valvetrain) that a coin can stand on it's edge on a running engine.
What problem is it that wants to be improved on?
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Re: Reciprocating weight tests ?

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SchmidtMotorWorks wrote: Thu Mar 09, 2023 11:02 am I'm curious, who believes that DVs claim that reducing mass increases rear wheel power?
Hint; The work being done was reduced, the power was not increased.

This can be computed more precisely than dyno or track testing can.
If dyno or track testing contradicts the computation, the testing is flawed.
Rear Wheel Power Increases - The Spin Zone
Here are eight ways to get big rear-wheel POWER INCREASES without having your ENGINE make one hp more.
David Vizard photographer Johnny Hunkins photographer
Dec 12, 2006
https://www.motortrend.com/how-to/0602p ... -increase/
There is power consumed by angularly accelerating a body, the power is given by = I x alpha x omega

where

I = mass moment of inertia (kgm^2)
alpha = angular acceleration (rad/s^2)
omega = rotational velocity (rad/s)

take a 10kg flysheel 12" in diameter accelerating from 2000-7000 in 7 seconds

the power consumed at 7000rpm is

I = 1/2mr^2 = 0.5*10*0.1524^2 = 0.116
omega = 7000 * 2 * pi / 60 = 733 rad/s
alpha = (733 - 2000 * 2 * p / 60) / 7 = 75 rad/s^2

power = 0.116 * 733 * 75 = 6377 watts = 6.3 kW
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Re: Reciprocating weight tests ?

Post by Stan Weiss »

The first dyno sheet is from the carb shootout on the BLP inertia dyno. Using just the RPM and time from that dyno sheet and a weight that I needed to select I get the second dyno sheet. My numbers do not match perfectly for a few reasons which I talked with Mike Laws about at that time.

Stan
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Re: Reciprocating weight tests ?

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digger wrote: Fri Mar 10, 2023 4:28 am
SchmidtMotorWorks wrote: Thu Mar 09, 2023 11:02 am I'm curious, who believes that DVs claim that reducing mass increases rear wheel power?
Hint; The work being done was reduced, the power was not increased.

This can be computed more precisely than dyno or track testing can.
If dyno or track testing contradicts the computation, the testing is flawed.
Rear Wheel Power Increases - The Spin Zone
Here are eight ways to get big rear-wheel POWER INCREASES without having your ENGINE make one hp more.
David Vizard photographer Johnny Hunkins photographer
Dec 12, 2006
https://www.motortrend.com/how-to/0602p ... -increase/
There is power consumed by angularly accelerating a body, the power is given by = I x alpha x omega

where

I = mass moment of inertia (kgm^2)
alpha = angular acceleration (rad/s^2)
omega = rotational velocity (rad/s)

take a 10kg flysheel 12" in diameter accelerating from 2000-7000 in 7 seconds

the power consumed at 7000rpm is

I = 1/2mr^2 = 0.5*10*0.1524^2 = 0.116
omega = 7000 * 2 * pi / 60 = 733 rad/s
alpha = (733 - 2000 * 2 * p / 60) / 7 = 75 rad/s^2

power = 0.116 * 733 * 75 = 6377 watts = 6.3 kW
hp = torque x rpm
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Re: Reciprocating weight tests ?

Post by Stan Weiss »

10# @ 6" radius Torque is constant because of a fixed rate of acceleration.

Stan
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Re: Reciprocating weight tests ?

Post by juuhanaa »

A less powerful car may need a lighter rotating mass for better acceleration.. but if you grab that flywheel it doesnt make torque.

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