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A 27-litre Merlin in 1/72nd scale scaleoramas out to 13.125 litres in 1/35th scale. <...>

Does it work that way with volumes? Okay, 1/72 is roughly half of 1/35. So, wouldn't a single "1/35 litre" have space for eight "1/72 litres"? Twice as long, but also twice as wide and twice as high? Wouldn't a 1/72 Merlin then have a displacement of just 27/8= 3.375 litres when used on a 1/35 build?

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Actually just 3.101 litres (when figuring actual 35/72=0.486 and not for simplicity's sake 35/72=0.5).

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Doh! Yes, you're right of course...

I suspect it's more complicated than that, because we're dealing with the volume of cylinders. The piston stroke is a straight dimension which scales linearly, but the bore of the piston has to be converted into an area to get the volume and that makes it a square function. I've run a few examples where I've taken cylinders of the same volume but different proportions, scaled them linearly, and worked out the new volume, and it comes out different. The conversion factor between the volumes comes out as anything from x 8.5 to x 8.75.

Having said that, that isn't a big range of conversion factors when you consider that engines can be bored out in the original block without changing their outward appearance. And all of this is, of course, good news for Zenrat, since it means he can use a much wider range of sub-scale aircraft engines (including 1/48th) to make 1/35th hotrods.

Conversion factor for 1/48th to 1/35th = 2.58