clarence kee specs on rossi 40 class engines
the ultrathusts come in three rpm ranges, the red is standard next up is the gold, then the black one. the different rossi's used the same timing on crank and intake ports, the exhaust duration was the only thing changed, I just examines some of my stock and this is the norm..so raise exhaust to 168-172 degrees, I checked my nelson sleeved Os 61 sx setup and they all use stock factory intake timing on sleeve, and they do rev like crazy and make tons of power, with excellent idle and transition , if you have more shims measure them all as you raise timing you lose dynamic compression, so check deck height 10-12 thou should be good/
I use the macs wizard, and the standard open pipe, I can post a pic of the header if you like, for length approximation.. here is the Clarence Lee review with timing specs for the .40, so its a good starting point, he advises the 170 degree timing mod for full pipe performance as well. i am trying to post Clarence Lee's review of the .40 rossi, it has all the timing spec as well as prop data