MEOW, there were two versions of the Enya .46, the original and the .46 MKII which had larger main bearings, I believe the front of the crankcase can be bought as a retro-fit to put the larger main bearings in the original. As Sky stated the .53 is happy turning a larger prop like a 12x6, the .46 MKII runs rich in the midrange with a 12x6 due to having to open the main needle farther to run the larger prop, I suspect that is due to the airflow velocity through the carb being slower. Randy Linsalata of RJL reworked the valve timing on the HP, it has considerably more power than when it was made in Austria, but still a shade soft. By the way, my Enya .46 MKII was my very first RC engine. It was run for its first three years on Fox 15% nitro fuel with 20% castor with no dire consequences.