Great question! Could it be a typo on the box / instructions ? I would email them and ask. They are usually prompt at responding, I have contacted them in the past with questions.

Another thing, have you even seen a 4 stroke built in that size?

edit - Saito makes a 40 4stroke, so ... my guess is the sizes for the engine type are swapped around. I would still email Sig..

E-mail for Order and Product Queries: [email protected]

http://www.sigmfg.com/cgi-bin/dpsmar...FV4.html?E+Sig