figuring displacement etc.

[grumpyvette]

I got asked about how to figure engine displacement and I figured there may be a need to find other info so....

get out your calculator

the formula is BORE x BORE x stroke X NUMBER OF CYLINDERS x .7854= displacement

DISPLACEMENT is the voluum of the cylinder formed by the travel the pistons displace between top dead center and bottom dead center times the number of cylinders, example if an engine had a 4" dia. piston and it moved down 3.48" between its upper and lower extremes that cylinder would displace, aproximately 43.73 cubic inches, eight of those in a sbc 350 would be the displacement 43.73 x 8 =349.8 or rounded to the nearest inch,to 350

EXAMPLE

4.030" bore times 4.030 " bore times 3.75" stroke times eight cylinders times .7854 = 382.7 OR a 383 sbc

heres other usefull calculators

http://www.csgnetwork.com/compcalc.html

http://www.angelfire.com/fl/procrastination/motor.html

http://www.4racecars.com/calculators/displacement_calculator.html

http://hotrodworks.net/hotrodmath/hotrodmath.html

http://www.diamondracing.net/cocalc.htm

http://users.erols.com/srweiss/index.html#jcalc

http://users.erols.com/dmapes/GEARCLC.HTM

http://www.doverusa.com/compression-height-calculator.htm

http://kb-silvolite.com/calc.php

http://www.bgsoflex.com/crchange.html

http://victorylibrary.com/mopar/intake-tech-c.htm


http://www.rbracing-rsr.com/runnertorquecalc.html

http://www.bgsoflex.com/intakeln.html

http://www.me.psu.edu/me415/SPRING02/intake/intake.html

http://headerdesign.com/extras/engine.asp#Intake_Manifolds

http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466

http://turbonation.com/intake.htm

http://cochise.uia.net/pkelley2/DynamicCR.html

http://victorylibrary.com/mopar/header-tech-c.htm

 

[geekinavette]

To answer the inevitable question....where does the (approximation) .7854 come from?

The exact formula for the area of a circle is

A = pi R^2
(Area is equal to pi times Radius squared).

Since R is equal to D(iameter), or Bore size, divided by 2...the formula can be written as:

A = pi (D/2)^2
(Area is equal to pi times the quantity: Diameter divided by 2; squared).

the (D/2)^2 factor can be simplified by applying the radical (^2) to both numerator and denominator of the D/2 fraction...yielding D^2/2^2 (D squared divided by 2 squared). 2^2 of course is equal to 4...so you get:

A = pi D^2/4 (Area is equal to pi times D squared divided by 4).

pi is now divided by 4 to yield the approximation of 0.7854, and the approximated formula becomes

A ~ 0.7854 D^2 (Area is approximately equal to 0.7854 times D squared).

Now taking the area and cylinder length to calculate cylinder volume...

V ~ 0.7854 D^2 L (Cylinder Volume is approximately equal to 0.7854 times D [bore] squared times length [stroke]).

Multiply this by number of cylinders to get total engine displacement.



Bill