IDRIVEAG8GT

Hey guys, I googled this and couldn't come up with much, but I have a math related question.

1. How do you figure displacement?

Thanks,
Robbie.

LPE 403

iTrader: (6)

http://www.race-cars.net/calculators...alculator.html

IDRIVEAG8GT

Bookmarking! Thanks LPE 403.

I'm headed off to New Mexico Tech soon for Mechanical and Mineral Engineering so if possible I'd really like to have the equations for both displacement and compression. Thank you

litle88

iTrader: (20)

here you go

http://wallaceracing.com/cr_test2.php

they have lots of calculators here

http://wallaceracing.com/Calculators.htm

Old SStroker

How close do you want to know? One of the online calculators above only goes to the nearest cubic inch.

What do you do if you don't have an internet hookup?

How about a simple way to do it on a hand calculator or the "tools" menu on your phone that's accurate to the 5th decimal place?

bore times bore times stroke times number of cylinders times .7854 = displacement.

Written as an equation: B x B x S x #Cyl x .7854 = D

You don't even have to remember .7854. It's the 4 numbers in the top left corner of a keypad run clockwise.

Try 4.000 bore 3.000 stroke and eight cylinders on you calculator or your phone, then on the "online calculator" above.

Now try a .005 overbore both ways.

FWIW:

For the math majors, .7854 is an "close approximation" of PI/4. (it is actually .785398163...). In the above example .7854 gives a displacement accurate to .011 cc on a 302 cubic inch V8 or .0014 cc per cylinder. Close enough, IMO.

"Teach a man to fish"


Jon

SSCamaro99_3

iTrader: (1)

I use this all the time becasue it is quick and easy to remember.

Actual formula D= ((bore diam X pi) x stroke) x number of cylinders. This can be jubbled in any order however, as it is technically a summation function (my math terms may be slipping some, as it has been a long time).

Old SStroker

No offense, but that only works for a 4.000 bore. I think you meant bore^2 x PI/4 x stroke x # cylinders= D.

Verbally it's the "area of the bore times the stroke times the number of cylinders equals displacement". Area of a circle is PI x radius squared [PI x r^2] "Pi r squared") or since radius = diameter/2, area = PI x diameter squared divided by 4 or [PI x d/2 x d/2].

BTW, your teacher was wrong when she said "Pie are squared".

If you are from the south you know that "Pie are round...cornbread are square."

Jon

Sales2@Texas-speed

iTrader: (5)

And if you're teaching a man to fish, it's worth mentioning that the formula you posted is simply another version of the very basic formula used in elementary school:

Area of circle x Height of cylinder = volume or displacement
-and-
Area of circle = Pi(r^2)

So (Pi)(r)(r)(Stroke or height)(#Cylinders) = Displacement
-next-
(Pi)(Bore/2)(Bore/2)(Stroke)(#cylinders)
-canceling the 2's with the 8 for your 8 cylinder engines-
(Pi)(Bore)(Bore)(Stroke)(2)

If you've got a calculator with the Pi button, and can't remember .7854 to save your life, that formula will do the trick as well and is pretty easy to remember. 3.14 or 3.1416 is close enough Pi if you don't have a "hi-tech" calculator laying around

Old SStroker

On a cellphone they are the numbers in the lower left corner run counterclockwise. My phone doesn't have PI in it's calculator, and .7854 is many orders of magnitude more accurate than 3.14. How does someone who doesn't understand the concept of PI even remember 3.14 unless it's his birthdate?

Unfortunately Matt, it is obvious that elementary or even high school graduates frequenting the net didn't learn this kind of thing. That is sad, but it is what it is. Even some of those who send 100+ text messages a day probably have never used the calculator function of their cell. At least it's with most of us 24/7 so it is available.

I'm trying to help them learn what their teachers failed to do. If someone is motivated enough to ask how to calculate displacement, for example, perhaps we can teach them a technique they can easily remember.

A least noone wanted to put rod length into the displacement calculation.

Jon

Sales2@Texas-speed

iTrader: (5)

Agreed Jon, neither my phone or calculator at work have the Pi symbol. And I like that you'd rather teach the formula than just link a website that will calculate it! We do need more of that in this world!

SSCamaro99_3

iTrader: (1)

None taken. I knew better, was posting at work, and checked my thought using the 4 in bore. Pays to check your work.

IDRIVEAG8GT

Holy crap! I didn't check this post in 2 or so days, and now I look at it and there's a wealth of the exact info I was looking for! thank you guys!

IDRIVEAG8GT

I understood the concept of using base circle (Pi) and stroke but wasn't sure how to figure those two into the number of cylinders that I have. Internet calculators are good, but I wanted the knowledge so if I was ever in a predicament where I didn't have it, I could do it with pencil and paper, or calculator, whichever is handy The variation that was posted is very simple and easy indeed.

So now, is there any way I could bug you guys on how to do compression?

IDRIVEAG8GT

Theoretically, to figure Compression Ratio, the formula is:

"Cylinder Volume + Clearance Volume + Piston Compression Volume + Gasket Volume + Chamber Volume (Divided by) Clearance Volume + Gasket Volume + Chamber Volume."

And since Piston Dishes and Combustion Chambers are measured in CC you have to convert C.I. to figure CR using (Value x 0.0610237) Right?

But besides Cylinder Volume (Listed Above "B x B x S x .7854") how do you figure out the rest of the formula and how do you derive Dynamic Compression out of that?

-Robbie.