Is it much different between a standard pork chop crank and a center balanced crank?
Asking for a friend.
Torsional Bending Frequency of a Hemi Crankshaft
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Torsional Bending Frequency of a Hemi Crankshaft
Anybody ever done any testing or Holzer calcs on a Hemi crankshaft to know where its first torsional bending frequency is?
Is it much different between a standard pork chop crank and a center balanced crank?
Asking for a friend.
Is it much different between a standard pork chop crank and a center balanced crank?
Asking for a friend.
Re: Torsional Bending Frequency of a Hemi Crankshaft
If I remember correctly Ithink when using Holzer calcs with a internal combustion engine the torque
is not in a steady state so multi-able Substantial errors can be incurred.
I Just found this PDF file hope it helps
http://www.engdyn.com/images/uploads/23 ... _-_frs.pdf
is not in a steady state so multi-able Substantial errors can be incurred.
I Just found this PDF file hope it helps
http://www.engdyn.com/images/uploads/23 ... _-_frs.pdf
Malvin
" Keep away from people who try to belittle your ambitions. Small people always do that but the really great make you
feel that you, too, can become great". By Mark Twain
" Keep away from people who try to belittle your ambitions. Small people always do that but the really great make you
feel that you, too, can become great". By Mark Twain
Re: Torsional Bending Frequency of a Hemi Crankshaft
Among other things, you can use a Audio Spectrum Analyzer app in your phone or laptop and tap the crank with a hammer to see what its natural frequency is when it rings. It is wise to avoid that frequency for extended time periods or use a harmonic balancer/damper tuned to that frequency. Recall the glass in the Memorex commercial. "Is it live or is it Memorex?"
Re: Torsional Bending Frequency of a Hemi Crankshaft
Ok, it took a while but here are my results after whittling out a Callies Crank in Solidworks and using a few FE softwares for modal analysis.
I also used Holzer tables to get an idea if they were in the ballpark compared to FE.
The results agree pretty well.
Next question:
Who runs RB and Hemi engines at the drag strip and what RPMs do you build them for?
Stroker or stock?
Analysis Results
I also used Holzer tables to get an idea if they were in the ballpark compared to FE.
The results agree pretty well.
Next question:
Who runs RB and Hemi engines at the drag strip and what RPMs do you build them for?
Stroker or stock?
Analysis Results
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Dan Timberlake
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Re: Torsional Bending Frequency of a Hemi Crankshaft
For my money any "free-free" analysis is kind of meaningless, especially for bending modes, since in real life the main bearings/block connect restrain the crank laterally to a considerable degree, similar to the way a guitar string plays a much different note when pressed against a fret.
A not-so-fun example is trying to balance a nice long vintage straight 8 crankshaft while supporting it at the end journals.
https://i.ebayimg.com/images/g/CVkAAOSw ... -l1600.jpg
Revved up to just a few hundred rpm the balance machine will dutifully report there is a significant "force" or single plan unbalance. Rev the crank up a little higher, and the "unbalance" will increase. That was because without the important constraining influence at each of the main bearings/block the crank could bow or whip.
Well, maybe it would be fun to "ring" the crank while suspended from a bungee cord, and monitored with a few accelerometers and a spectrum analyzer just to see how well the "free-free" result compared.
In the table on the your webpage it looks like you focused on the 4th order excitation ( 8 cyl 4 stroke firing frequency).
In a few SAE papers they arrived at the conclusion that the 4th order is the one that would likely wind the crank up the most.
Those same papers also showed how effective a basic damper was at sucking out the energy and taming response at resonance.
I believe the several pounds of steel loaded on each rod journal would possibly have the effect of numerically lowering the torsional resonant frequency.
FWIW in the 1966 SAE Hemi paper by Chrysler they chose a damper tuned to just 280 cps. I don't believe they mentioned what the torsional response of the crank assembly was under power.
The 1955 Chevy V8 paper does.
A not-so-fun example is trying to balance a nice long vintage straight 8 crankshaft while supporting it at the end journals.
https://i.ebayimg.com/images/g/CVkAAOSw ... -l1600.jpg
Revved up to just a few hundred rpm the balance machine will dutifully report there is a significant "force" or single plan unbalance. Rev the crank up a little higher, and the "unbalance" will increase. That was because without the important constraining influence at each of the main bearings/block the crank could bow or whip.
Well, maybe it would be fun to "ring" the crank while suspended from a bungee cord, and monitored with a few accelerometers and a spectrum analyzer just to see how well the "free-free" result compared.
In the table on the your webpage it looks like you focused on the 4th order excitation ( 8 cyl 4 stroke firing frequency).
In a few SAE papers they arrived at the conclusion that the 4th order is the one that would likely wind the crank up the most.
Those same papers also showed how effective a basic damper was at sucking out the energy and taming response at resonance.
I believe the several pounds of steel loaded on each rod journal would possibly have the effect of numerically lowering the torsional resonant frequency.
FWIW in the 1966 SAE Hemi paper by Chrysler they chose a damper tuned to just 280 cps. I don't believe they mentioned what the torsional response of the crank assembly was under power.
The 1955 Chevy V8 paper does.
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Circlotron
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- Location: Melbourne, Australia
Re: Torsional Bending Frequency of a Hemi Crankshaft
^^ That 1955 Chevy V8 paper, where can I find a copy?