Looking for the cc to mm for big bore kits?

[DorkoElite303]

Wow, alot has been going on since the last time I posted.

ANywho..can anyone tell me the measurements of the big bore kits. Saying 70cc equals to a 48mm bore?

65cc= ?mm
70cc=?mm
75cc=?mm
85cc=?mm
100cc=?mm

And any other big bore kits.

[Bear45-70]

They don't convert straight across. CC stands for Cubic Centimeters a measure of volume. MM stands for MilliMeters and is a measure of linear distance. The formula is;

Volume (in cubic milimeters) = Pi (3.14) times Radius of the Bore (in mm) squared times the stroke (also in mm)

For a Spree....Bore is 41.0 mm X 37.4 mm Stroke

20.5X 20.5 = 420.25 X 3.14 = 1319.585 X 37.4 = 49352.479 cubic millimeters divided by 1000 = 49.3 cc

That is the only way they convert.

[Wheelman-111]

Greetings:

The Bear is exactly right. I would add that the engine displacement cannot be calculated unless you know the STROKE Of your engine as well as its BORE size.

The later Aero models for example had the same stock dimensions as the Spree he described: stock bore of 41 mm.x a relatively short stroke of 37.4 mm. The biggest cylinder that engine can accommodate (without machine shop work, anyway...)is 47 mm,

As diameter is twice the radius so 23.5 is the working number. Square it and you get
23.5 x 23.5 = 552.25

Our old pi value of 3.1416 takes tha to
552.25 x 3.1416 =1735 square mm of piston AREA.

To get the final cylinder VOLUME we need to multiply that by the STROKE:

1735 x 37.4 = 64887 or roughly 65 ccs.

You didn't say what model you had. '94 & later SA50s got their 50 ccs using a smaller piston and a longer STROKE. That's one reason why the same 47 mm piston yields a larger (like 72 cc) displacememt.

Look up your stroke dimension in the technical documents-usually in the front of the service manual under Specifications.

Then piR squared x stroke and you'll know your size.

[DorkoElite303]

Oh I know they don't convert straight accross. I guess I meant to say is...does anyone know the sizes of the bore kits for the 94+ elites.

[DorkoElite303]

Sorry...just read the last comment. So Saying I was looking on ebay for a bore kit and came accross a kit that said 100cc bore it 51mm. Are they talking about a 51mm stoke then???

[Wheelman-111]

Greetings:

To get 100cc with a 51 mm bore, you would need a 49mm stroke.

Just plug the numbers into your calculator:

R squared x pi x Stroke= cylinder volume.

51/2 = 25.5
25.5 x 25.5 x 3.1416 x 49 = 100

It's 'rithmetical. Not hard to do.

[Dac]

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


stock crank= 41.2mm
stock piston= 39mm

Enter info like this....

[Dac]

example is....

41.2mm crank + 39mm bore = 49cc
41.2mm crank + 47mm bore = 72cc
41.2mm crank + 50mm bore = 80cc

But, once you start swapping the cranks, thats when the CC's really start to build up.

[maddog]

for mini stroker cranks it goes 41-42-43-44.7 which is what i run= 76cc