As far as I am aware, there is no absolute formula for speed against engine size. There are many rough guides, with the actual limiting factors being, the valve gear, inertia in moving parts, and general inefficiency, plus the normal design criteria. At a guess, that size of engine would probably turn at around 500-600 rpm without too much trouble. It is quite a long stroke for the bore, which will limit speed. Alan ----- Original Message ----- From: "Pcx" <pierre.courbouleix@xxxxxxxxxx> To: <modeleng@xxxxxxxxxxxxx> Sent: Tuesday, September 06, 2005 7:24 PM Subject: [modeleng] Tr: Re: Steam engine RPM ? > Hi All, When discussing with a friend we had this question ( may seem crazy to the most experienced of You), for which we found no reliable answer, how to calculate (estimate?) the running speed of a steam engine (RPM) knowing the type of engine (single/double acting, condensing/non condensing), the stroke,the bore and the inlet steam pressure ? For your info we are building an horizontal slide-valve steam engine 1 1/2 bore, 2 1/4 stoke , of a type inspired from an old design . > I thank you for your help and the infos you can forward .... > Regards > > pierre.courbouleix@xxxxxxxxxx > Pierre MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.