What??? they had a 53 some years ago, it had a cylindrical head and case and indeed it was a dog ( I had it) Is this a new 53 with the square head and case?? I didn`t see it in the Peak site. My 52 xls spins the 12.25-3.75 APC at 13700 rpm, and the 12-4 APC at 14100 rpm, ok I use the Tower muffler and have removed a headshim plus some minor sleevework, but I mean to remember it will swind that 12.25 prop about 12800-13000 rpm stock. A friend have just bought a new 52 xls (bone stock), so I will tach it as soon as we have some daylight again up here.