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Unread 01-22-2009, 09:21 PM   #1
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Default I need a Formula

mainly this is directed to Mr Car Guy but anybody is welcome to chime in I need the formula to canculate compression and engine displacement. Exactly what info is needed if changing parts to aftermarket what info is needed and what do I take into account I had this info ounce but never made use of it so i'm alittle lost./ thanks and I know this isn't the same formula i'm looking for both.
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Unread 01-23-2009, 02:27 AM   #2
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I haven't had to calculate this in a while.

You need the following information;
  • Cylinder diameter
  • Crankshaft stroke
  • Compressed head gasket thickness
  • Combustion chamber cc's
  • Piston volume
  • Deck height


Here's a couple online calculators I have used;
http://www.csgnetwork.com/compcalc.html
http://www.rbracing-rsr.com/compstaticcalc.html - this one has some useful info too

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Unread 01-23-2009, 06:05 PM   #3
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i'm planning on stroking a 2.3L quad 4 out to 2.6L but it's gonna take custom piston and i need to figure on what compression to run. Currently my car has a 2.4L i'm going to take that crank and buy a reman 2.3L LGO light wieght rods and custom pistons I figure at 11.5.1 I should end up with a 230HP 2.6L but I need to stop figuring and do the math.
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Unread 01-23-2009, 11:59 PM   #4
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Sounds like a nice project, keep us updated
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Unread 01-26-2009, 02:17 AM   #5
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Quote:
Originally Posted by lautinjr View Post
mainly this is directed to Mr Car Guy but anybody is welcome to chime in I need the formula to canculate compression and engine displacement. Exactly what info is needed if changing parts to aftermarket what info is needed and what do I take into account I had this info ounce but never made use of it so i'm alittle lost./ thanks and I know this isn't the same formula i'm looking for both.
Hi,

Engine displacement =

Bore x 3.14 x 8 x Stroke = Cubic Inches 3.14 = Pi 8 = number of cylinders

Example: 327 Small block Chevy

4.00 x 3.14 = 12.56 sq in x 8 = 100.48 x 3.25in = 326.56cu in

Example: 400 Pontiac

4.25 x 3.14 = 13.345 x 8 = 106.76 x 3.75 = 400.35 If you bore the engine out .030"
4.28 x 3.14 x 8 x 3.75 = 403cu in So a .030 over bore = 3 cu inches to the motor.

The calculation for determining compression ratio works out like this:

CR=(D + PV + DC + G + CC) / (PV + DC + G + CC)

CR = Compression Ratio

D = Displacement

PV = Piston Volume

DC = Deck Clearance Volume

G = Gasket Volume

CC = Combustion Chamber Volume

There are a lot of variables here...

I hope this helped, :-)

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