Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

We have all seen engines marked as a certain displacement, only to find the math doesn’t add up when calculated from the bore and stroke.  A recent engine builders forum took a builder to task because a classic design billed as 10cc measured out to 9.35cc.  Turns out, the designers purposely made the engine such 5hat it could be bored out and re-ringed twice and still not exceed the 10cc displacement that limited the class it competed in.   If you want to race in the 10cc class, a re-ringed and cleaned up 10cc engine ends up over, which you don’t want to suffer if challenged.  So maybe it wasn’t simply a fisherman’s ruler in use after all.