Engine Displacement Calculation - HELP

[Muzz2676]

I've been a car enthusiast for years but realise i know very little about the mechanics. I've gone off and done a bit of research on engines and ended up reading about how you work out engine displacement which was very interesting and i understand is:

(pi /4 x bore squared x stroke x number of cylinders) / 1000

Using the Wiki pages here I worked out the m20b25 with a 84mm bore and 75mm stroke

(0.7854 x 7056 x 75 x 6) / 1000 = 2494 cc which is correct

I then worked out a 2.7 stroker with 84mm bore and 81mm stroke:

(0.7854 x 7056 x 81 x 6) / 1000 = 2693 cc which i guess is about right

I then tried to work out the m20b20 which apparently has an 80mm bore with 71mm stroke according to the m20 wiki:

(0.7854 x 6400 x 71 x 6) / 1000 = 2141 cc which is very wrong.

Sorry to be a 'bore' but it's driving me nuts so thought i'd ask where i've gone wrong.

Please put me out of my misery.

Thanks
Ian

[Muzz2676]

I've worked it out, i think the Wiki is wrong it states:

320i - 71mm stroke
323i - 76mm stroke
325e - 81mm stroke
325i - 75mm stroke

When the m20b20 is 66mm stroke which then gives 1991 cc which is correct

[flybynite]

I've worked it out, i think the Wiki is wrong it states:

320i - 71mm stroke
323i - 76mm stroke
325e - 81mm stroke
325i - 75mm stroke

When the m20b20 is 66mm stroke which then gives 1991 cc which is correct

Correct the M20B20 has 66mm stroke The M20B23 actually has a 76.8mm stroke, hard sums to work that out

No-one probably noticed because the B20 crank is useful for nothing other than a large paperweight. People use the rods and bin the crank.

[martauto]

You could use this.

Piir2h x 6

Where as
Pii (3.142)
r2 (radius of bore squared)
h (stroke)
6 (six cylinders)

But you Nerds knew that and kept quiet

Great to have another Nerd on board

Mart.

[coopman]

I prefer the original result. I like the idea that my 320i is 2141 cc.

[flybynite]

You could use this.
Piir2h x 6

Yes but I can't seem to get that to work when they change a 330d to a 340d still seems to end up at 3000cc

[Muzz2676]

No-one probably noticed because the B20 crank is useful for nothing other than a large paperweight. People use the rods and bin the crank.

Tbf no-one is probably as sad as me!!!!

[martauto]

No-one probably noticed because the B20 crank is useful for nothing other than a large paperweight. People use the rods and bin the crank.

Tbf no-one is probably as sad as me!!!!

Well, maybe one more.

Mart.