ST had an adendum for the fuel requirements (which I have) some while back on the "Big" Tigres. They say to use 10 to 12% ALL castor oil or 18% synthetic/castor blend. I like Flyboy Dave run 15% nitro and 18% blend. I have 2 2500s and 1 2000. My most run 2500 turns a Mezjlik 18X8 at 8900rpm. Several years ago I spoke to Bill Baxter a.k.a. "BAX" and he was running a ST 4500 on 30% nitro for racing.