The MVVS will run with the rest of the strong 40s but not with a Rossi 53. I've only compared the Rossi 53 with a Rossi 40 on a 12/4 apc and the Rossi 53 is good for about another 1000 rpm on 5% nitro. The Rossis don't like much more than that. But then the 53 is closer to 200 bucks than the 40 is to a 100 bucks. They are both great running engines.
But did I mention they are both LOUD, LOUD, LOUD on their stock mufflers. I did compare a Webra 50 with an Mvvs 40 on my Balsa Nova and the MVVs gave up nearly a 1000 rpm to the Webra also on a 12/4.

Denis

Jaka
I forgot to mention I think you are thinking of the old Rossi mufflers. The new ones seem to be well made and durable. They do use this screwy spring to hold it on. I don't use that. I use a fuselage stand off. Oops more weight.

Denis

Denis