I used o'donnel for a while. I didn't like the performance on the new engine. It was great during break-in but seemed to bog down after break-in was done, even afer retuning. Since then, I've been running Byron's 20% and the "snap" is back in the engines that I use. I guess it's a hit or miss. There's lot's of variables for performance but preference is also key. Byron's also seems to burn cleaner and doesn't have that funky smell of O'donnels.