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Old 11-17-2020, 04:56 PM   #1
firerod
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Default Cubic inch question

I have a Ford 8ba that has been bored .040 over and has a Merc. crank. What cubic inch does this come out to? Thank you and sorry for my ignorance.
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Old 11-17-2020, 05:16 PM   #2
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Default Re: Cubic inch question

261.8 (let's call it a 262).
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Old 11-17-2020, 05:30 PM   #3
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Default Re: Cubic inch question

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261.8 (let's call it a 262).
That tubman sure knows how to punch a calculator....on the money! DD
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Old 11-17-2020, 06:52 PM   #4
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Default Re: Cubic inch question

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That tubman sure knows how to punch a calculator....on the money! DD
Yeah, but I didn't have to look up the mathematical formula required. When I was in college taking physics, calculating devices (slide rules in my day) were OK during tests. They were checking your knowledge of Physics, not your math abilities.

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Old 11-17-2020, 07:27 PM   #5
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Default Re: Cubic inch question

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Yeah, but I didn't lave to look up the mathematical formula required. When I was in college taking physics, calculating devices (slide rules in my day) were OK during tests. They were checking your knowledge of Physics, not your math abilities.
I've known that formula (by heart) since junior high. And I do it the ".7854" way. DD
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Old 11-17-2020, 08:21 PM   #6
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Okay, I'm game. What does that fraction represent. Never did that well in physics. Terry
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Old 11-17-2020, 08:32 PM   #7
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Default Re: Cubic inch question

So is my .080 over gonna be 269?
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Old 11-17-2020, 09:16 PM   #8
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Default Re: Cubic inch question

268.33


(pi X bore radius squared x stroke x 8)
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Old 11-17-2020, 09:38 PM   #9
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Default Re: Cubic inch question

Thanks cad, guess I better say 268.
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Old 11-17-2020, 10:13 PM   #10
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Default Re: Cubic inch question

Thanks, that's what I came up with but was told it was wrong.
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Old 11-18-2020, 01:35 AM   #11
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Okay, I'm game. What does that fraction represent. Never did that well in physics. Terry
Hey Terry....

OK, "0.7854" is a function of pi, accurate to at least four decimal places.

0.7854 = 3.1416/4 or (3.1416 divided by 4).

Example: Bore X Bore X Stroke X .7854 X 8 (cyls.) = Cu. In.

Your FIRST Example:

Bore = 3.1875 + 0.040 = 3.2275

Stroke = 4.0

Constant = .7854

Number of Cylinders = 8
__________________________________

So: 3.2275 X 3.2275 X 4 X 0.7854 X 8 = 261.80224
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Old 11-18-2020, 02:00 AM   #12
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Default Re: Cubic inch question

I do it slightly different.

I punch in the bore (3.2275), then I hit the squared button ( ), after that, I multiple by .7854, then times stroke (4) and finally, times 8 = 261.80225148

Darn, I got a different answer, what happened

One of the nice things about using .7854, is that on number pads, it is the top, left hand corner keys. Makes it a little easier for me.
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Old 11-18-2020, 03:04 AM   #13
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Default Re: Cubic inch question

It would take me 10 years to understand why you square the bore measurement.
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Old 11-18-2020, 03:38 AM   #14
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Default Re: Cubic inch question

You square it because you want the area of the cylinder.

Area of a circle is Pi r squared.

Because we know the bore rather than the radius, we have to use the alternative formula that uses the diameter.

Area of a circle is pi d squared all over 4. (over = divided by)

Volume of one cylinder of a stock 239 for example is:

3.1875 * 3.1875 * 3.1416 / 4 Which equals 7.9798. Unit is square inches.

Volume of a cylinder = area * length.

So 7.9798 * 3.75 = 29.9242. Now the unit is cubic inches. So just shy of 30 cu in.

Volume of the engine is volume of one cylinder times the number of cylinders.

So 29.9242 * 8 = 239.3936

Rounded to 239 for ease of reference.

I used a known engine because we are already familiar with the answer.

In the examples above the shortcut is to use pi/4. 3.1416/4 = .7854.

The above formulae are completely universal and by using centimeters the volume in cc can be calculated.

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Old 11-18-2020, 04:29 PM   #15
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Default Re: Cubic inch question

thanks, fellas. Terry
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Old 11-18-2020, 05:20 PM   #16
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Default Re: Cubic inch question

In my dotage now, my sliderule days are long forgotten, but you can do more today with a $6.99 drugstore calculator than the best sliderule ever made.
My old sliderule was never much good for making straight lines anyway, with that bumpy thingy right there in the middle.
I will say though, I had a round one once that helped me earn free pizza in my sports car rally days. (Back in the day, you'd have to tell them if you didn't want anchovies.)
Come to think of it, I guess I could have used my sliderule to determine how much beer was in a "'Yard of Beer' Stein".
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Old 11-18-2020, 05:25 PM   #17
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Default Re: Cubic inch question

Mart,


With respect, if we know the bore diameter, we automatically know the radius as it is one half of the diameter.
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Old 11-18-2020, 05:33 PM   #18
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Default Re: Cubic inch question

Who says one only remembers 5 minutes of what they learned in 5 years of college?

You guys have proved them wrong��
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Old 11-18-2020, 05:52 PM   #19
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Who says one only remembers 5 minutes of what they learned in 5 years of college?

You guys have proved them wrong��

Aw, I retain very fond memories of a few 5 minute sessions in college!
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Old 11-18-2020, 06:05 PM   #20
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Who says one only remembers 5 minutes of what they learned in 5 years of college?

You guys have proved them wrong��

Determining the area of a circle is taught about grade 6 or 7.
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