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Author Topic: Engine size designation  (Read 1667 times)

Offline Gene Elliott

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Engine size designation
« on: October 12, 2006, 10:41:48 AM »
I'm going to bear my ignorance here and ask if someone would explain the numbered designation for motors. What does the cubic inch displacement number actually measure? What does that refer to? And it's possible that the piston diameter on my OS 40 is a different size from the piston diameter of my Fox 40, right? Thanks for your input.

Gene Elliott
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Offline Ron King

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Re: Engine size designation
« Reply #1 on: October 12, 2006, 11:05:51 AM »
Gene,

Displacement is merely the volume of liquid that would be displaced (forced out) in the cylinder if the piston was moved from the bottom of the stroke to the top. It's measured in cubic numbers, either centimeters or inches.

Our engines are very small compared to an automobile engine. The old small block Chevy engine displaced 283 cubic inches, spread over eight cylinders (roughly 35 cubic inches per cylinder). Our model aircraft engines are typically single cylinder and displace much smaller amounts of liquid. For example, a Super Tigre .51 engine displaces just over 1/2 cubic inch.

Displacement  is calculated by taking the area of the cylinder ("PI R square" - remember that one?) and multiplying that number by the distance the piston travels up the cylinder (stroke).

Hope this helps,

Ron
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Offline Dick Fowler

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Re: Engine size designation
« Reply #2 on: October 12, 2006, 12:57:49 PM »
..."The old small block Chevy engine displaced 283 cubic inches, ..."


Come on Ron, we all know that they were 265 cu. in. or are you too young?  <=
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Offline Ron King

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Re: Engine size designation
« Reply #3 on: October 12, 2006, 01:39:14 PM »
Quote from: Dick Fowler on October 12, 2006, 12:57:49 PM
..."The old small block Chevy engine displaced 283 cubic inches, ..."

Come on Ron, we all know that they were 265 cu. in. or are you too young?  <=

Touche.  ~> You are correct. Forgive my Senior moment. They started at 265 and eventually got bored out to 327 cubic inches. Great engine design.

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Ron King
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Offline Bill Little

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Re: Engine size designation
« Reply #4 on: October 12, 2006, 01:49:18 PM »
Quote from: Ron King on October 12, 2006, 01:39:14 PM
Touche.  ~> You are correct. Forgive my Senior moment. They started at 265 and eventually got bored out to 327 cubic inches. Great engine design.

And on out to 350. :D There is a 400 small block Chevy!  They are all of the same block as the 265.

Bill <><
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Offline Mike Spiess

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Re: Engine size designation
« Reply #5 on: October 12, 2006, 02:22:07 PM »
Yea tiny when compared to a caddy 500
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Offline Gene Elliott

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Re: Engine size designation
« Reply #6 on: October 12, 2006, 02:44:11 PM »
What a mill! We have some serious car enthusiasts here.

Ron, thanks for the good explanation. . ."the volume of liquid that would be displaced" . . .It seemed to me a curious way to measure the size of an engine, but the more I think about it - it does measure the size. I was a college Spanish teacher and math and sciences were not my cup of tea.

Thanks Ron,
Gene
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Offline Bill Little

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Re: Engine size designation
« Reply #7 on: October 12, 2006, 03:54:12 PM »
Hi Gene,

I guess you got the "displacement question" answered, so the other ones you asked are what I will dwell on. ;D

A "40' engine is four tenths or fourty hundreths of a cubic inch displacement, and an .049 is fourtynine thousandths of a cubic inch displacement.  The new rule allowing .90 engines in stunt gives us almost a one cubic inch engine!

As to the pistons and such of one maker to the other, they can vary quite a bit in diameter since the "stroke" of the engine is the other 1/2 of the equation for measuring displacement.  And, as you know, I do not know of a model airplane engine that displaces exactly what the engine has marked on it.  For instance, a .40 might actually have a displacement of .3978.

Bill <><
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Offline Harry Rice

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Re: Engine size designation
« Reply #8 on: October 12, 2006, 04:44:24 PM »
Hi Folks,

Technically, it is called the "swept volume", which is, as previously said, the bore area multiplied by the piston stroke. (i.e. bore dia squared multiplied by Pi, divided by 4, and that result multiplied by the maximum travel of the piston - keeping the units the same - inches or metric).

Oh, and the above multiplied by the number of cylinders if more than one.....

Happy motoring (or flying!)

Cheers


Harry

forgot to mention - original engines tend to be smaller to allow for first rebore, so the engine does not go above the original quoted capacity.

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Offline Gene Elliott

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Re: Engine size designation
« Reply #9 on: October 12, 2006, 08:51:15 PM »
ˇGracias hermano Bill!

Gene
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Offline Bob Zambelli

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Re: Engine size designation
« Reply #10 on: October 13, 2006, 10:43:58 AM »
How about a 90 cubic inch V-12?
 f~
Bob Z.
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Offline Bill Little

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Re: Engine size designation
« Reply #11 on: October 13, 2006, 01:44:00 PM »
Quote from: Bob Zambelli on October 13, 2006, 10:43:58 AM
How about a 90 cubic inch V-12?
 f~
Bob Z.

What year did Ferrari make that one?  Looks early late '50s-early '60s.  ??? ??? ???

Bill <><
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Big Bear <><

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Offline Mike Spiess

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Re: Engine size designation
« Reply #12 on: October 13, 2006, 08:36:03 PM »
Yea but my caddy is in my garage waiting to be put in a rat truck. f~ AP^
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Offline RandySmith

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Re: Engine size designation
« Reply #13 on: October 14, 2006, 11:56:41 AM »

Hi Gene,
I guess you got the "displacement question" answered, so the other ones you asked are what I will dwell on. ;D
A "40' engine is four tenths or fourty hundreths of a cubic inch displacement, and an .049 is fourtynine thousandths of a cubic inch displacement.  The new rule allowing .90 engines in stunt gives us almost a one cubic inch engine!
As to the pistons and such of one maker to the other, they can vary quite a bit in diameter since the "stroke" of the engine is the other 1/2 of the equation for measuring displacement.  And, as you know, I do not know of a model airplane engine that displaces exactly what the engine has marked on it.  For instance, a .40 might actually have a displacement of .3978.

Bill <><
Quote

Hi Gene  Hello Bill

Actually  the new  size  aloows  bigger than a  90, we  can  go to a  .9153,  or  a   92  , rounding  the  size  off.
Of Course  don't  forget to make up those  21  thou  line  LOL

Regards
Randy
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