devinwwu

Ok, so i need someone to check my theory here.
I have a stock 3vze block that i am boring .040" over.
I was trying to figure out what my end displacement would be...

Here are my calculations.
According to 4x4wire, the stock bore is 87.5mm and stroke is 90mm. I tried calculating this out and it doesn't equal the 2958cc that is listed on the spec sheet...

Pi(Radius of Bore)^2 X Stroke = Volume of Cylinder
Pi(87.5/2)^2 x 90 =
6013.21875 x 90 = 541.189 cc per cylinder X 6 cylinders = 3247 CC Total

So i assumed the stock stroke listed is wrong and re-computed trying to find the correct stroke using a known total displacement of 2958CC.
I came up with a stock stroke of 81.986mm (not 90mm)

According to this, my oversized bore would take the motor up from 2958cc to 3027cc.

.040" = 1.016mm
Oversized bore = 88.516mm
Radius = 44.258mm

Pi(44.258)^2 x 81.986 = 504.51 cc per cylinder X 6 cyl = 3027 CC Total

You guys following me?
Remember that you need to convert mm > cm (mm/1000)

My real question is does anyone know what the stock bore and stroke really are?? either those are listed wrong on 4x4wire or the total displacement is, but i am pretty sure my math is right...

devinwwu

ps. yes i'm bored at work and i realize that at the end of the day its still a 3.slow, i'm just curious, so when people ask me i can tell them intelligently about the displacement

91diesel

check the math, it is pi*(r^2) not (pi*r)^2. I don't know that you did that......

devinwwu

i'm using my crappy computer calc so i had to compute the r^2 first and then multiply it by pie so we're ok there...

eric-the-red

My manual lists the bore as 87.4mm and the stroke as 82 mm. If you assume the 2958cc is correct then the new dispacement will be the original displacement multiplied by the new bore divided by the original bore, which is 2958 x 88.4/87.4 = 2992cc.

devinwwu

How do you figure? the only way to calculate volume of a cylinder is to use pi(r^2). dividing by the diameter of the bore would not give you an accurate answer. That way would work if you were stroking the motor and using the difference in stroke lengths to calculate total cc's.


That is interesting that the manual lists the bore and stroke differently than 4x4wire, but are you sure the bore is larger than the stroke? or is it the other way around?

eric-the-red

I wasn't actually calculating the volume, I just assumed the 2958 was correct. If you already have the volume then the new volume is simply the ratio of the new bore to the old bore multiplied by the original volume. The stroke and pi are both constant so don't need to be factored in.

And I double checked the manual, the bore is larger than the stroke. Of course the manual could be wrong.

mastacox

The volume of the cylinder is proportional to the radius of the cylinder squared, not just the radius of the cylinder (V = pi * r^2 * h). The OP is finding the difference correctly, by adding the over-bore to the original bore, and recalculating the volume.

Based on a bore of 87.4mm, and a stroke of 82mm, the displacement calculates to 2951 cm^3, which is pretty close to the quoted displacement of 2958 cm^3. Considering the bore's diameter is only given to us to 2 significant digits, and the stroke is only given to 3 sig figs, we have arrived at the correct displacement (if each measurement was given to four significant digits, e.g. XX.XX mm, we would probably get the exact right number).

So, if you add .040in to the bore, your new displacement is 3020 cm^3, or an additional 69 cm^3 (4.2 in^3). This equates to a 2.3% increase in total displacement from a 1.1% increase in total bore, further showing that the increase in volume with respect to bore is not a linear ratio.

devinwwu

^^ well done sir, and thank you for answering my question!

abecedarian

and don't forget to include the combustion chamber volume and piston dish volume (if equipped)