Building a vacuum accumulator, size question...?
 

Hi guys, I want to build a small vacuum accumulator tank/reservoir of my 944cc V-twin Ducati.

A bit of google bashing has given me an idea of what to build, but I don't know what capacity?

Is there a rule/ratio...?

If it were me, I'd make it about the size of a beer can and wrap a vinyl sticker around it of your favorite beverage. My '73 Beetle (2 speed auto) used vaccuum to shift from low to not-so-low and had a chamber of about a quart if I remember correctly.

If you are just trying to smooth out the readings on a vacuum gauge, you might just try a restriction by the engine side of the hose so that the hose itself acts as an "accumulator". Don't put something together that the engine can injest. Maybe a bit of dowel rod shoved in the hose that you drill out progressively till you are happy with the readings.