Piston Compression height formula

very simple formula
Deck height - rod length - (.5 of stroke)
for all you math challenged people:

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


change the numbers around to see what changes.....with different length rods and strokes...

Just to clarify, this does NOT give you the compression height of the piston. For that, you measure from the inside top of the pin hole to the top of the piston and add 1/2 the pin diameter

69 that is the exact formula to use.
example for many 572 engine combos 4.5 bore 4.5 stroke 1.156 1.094 1.031 or .990 pin diameters. ALL THE SAME.

10.7250 -6.865 - 2.25 = 1.61
10.7250 -7.100 -2.25 = 1.375
10.7250 -7.150 - 2.25 = 1.325

piston pin diameter has nothing to do with compression heigth only the location/size of the ring package.

That is what the calculator does for you (the math).
Please post your formula and a link for verification.

Example from Lunati
Compression Height Calculation
How Compression Height Is
Calculated
COMPRESSION HEIGHT=
BLOCK HEIGHT - ROD LENGTH - (0.5 X STROKE)
EXAMPLE:
Block Height = 11.685"
Rod Length = 7.500"
Stroke = 5.500"
Compression height = block height - rod length - (0.5 x
stroke)
Compression height = 11.685 - 7.500 - (0.5 x 5.500)
Compression height = 1.435"

PLEASE POINT OUT WHERE THE PIN DIAMETER IS INCLUDED IN THE FORMULA :rolling:

I'm speaking of the piston itself. NOT the over all compression height. It isn't uncommon for people to know what the compression height of the piston itself is....such as when buying replacement pistons for a 340.

You HAVE to know what that distance is. If not, then the rest of the measurements mean nothing. Measure the deck height, stroke, rod length, and NOT KNOW how tall the piston itself it?

YOU really must be kidding:rolling:

That is the compression height formula for a piston, ANY PISTON ...As stated 2 times before, is determined by the block height, rod length, and stroke of the engine it is going in....HAS NOTHING TO DO WITH PIN DIAMETER.

100% of the piston manufacturers use it...

NAME YOUR PISTON MANUFACTURER, AND POST A LINK TO THEIR FORMULA... IF YOU CLAIM IT IS WRONG....:blush::blush::blush:

The compression height of the piston itself is from the center of the pin to the top of the piston. THEREFORE you have to know what the pin diameter is in order to do a proper measurement

Taken from Summit

Brand: Keith Black/KB Pistons
Product Line: Keith Black Hypereutectic Pistons
Part Type: Pistons
Part Number: UEM-KB243030-8
Bore (in): 4.070 in.
Bore (mm): 103.378mm
Piston Style: Flat top, with two valve reliefs
Piston Material: Hypereutectic aluminum
Compression Distance (in): 1.840 in.
Piston Head Volume (cc): +6.00cc
Wrist Pin Style: Floating
Pin Diameter (in): 0.984 in.
Piston Ring Thickness: 5/64 in. x 5/64 in. x 3/16 in.
Quantity: Sold as a set of 8.
Notes: High compression. Approximate flattop factory compression ratio: 10.2:1.

Everyone hang on. GOD is going to bitch about me using an incorrect term in order to keep himself from being proved WRONG

and the equation Keith Black used to make those pistons is?????

DH-RL-(.5Xstroke)= piston compression height or Compression distance

The diameter of a pin, DOES NOT MOVE THE CENTER POINT (ya know where they start to measure from) and does NOT move the other point, (top) the compression distance or height.

Explain those little FACTS away.

Show these people where the diameter of a pin moves either the measuring points.

Pull your pants up, something is showing....:tongueflap::yes:
But your post count is rising....:grin:

The "equation" KB used is exactly what I said in my first response.

Would you like me to cut and paste it for you to read again?....But since you didn't get it the first time, I'm guessing you wouldn't get it a second.

But if you really have to have an equation......

C= inside top of pin hole to piston top
P= pin diameter
X= compression distance

C + (1/2P) = X

That is one way to measure an EXISTING piston NOT the formula to calculate the piston height on a new, to be manufactured piston.

The piston pin diameter has a center point. That center point is what is determined in the formula, NOT THE DIAMETER OF THE PIN.

One can choose from many different diameter pins when the compression height is determined.

You never mentioned a "new, to be manufactured piston" until now. I was talking about measuring a piston. I was always talking about measuring a piston.

Not sure what part of that you missed

TRY READING THE THREAD TITLE NEXT TIME

from your first post and 100% incorrect:
"this does NOT give you the compression height of the piston"

Supply the required variables and yes it does, 100% of the time......

you two obviously have a deep fondness for each other. your banter is both humorous and educational. c'mon guys- garage>computer-lighten up!

No it doesn't. It doesn't tell you anything except the difference between the center of the small end of the rod and the deck height.

End of discussion