I've been running them for about 4,000 miles and they are quiet. The alloy is 2618 so .003" is considered tight. I like to use 4032 pistons with minimum clearance but they just weren't available for a big bore. Diamond made these for me as a shelf item with 2 changes. Each change was $50. I needed a piston for a 3.701" bore with a 3v exhaust relief and 1.200" compression height. I also wanted flat tops. Diamond had the easiest process I could find for ordering a special piston so that's what I went with. It was as easy as calling cnc motorsports in Brookings, SD and placing the order. It took less than 5 minutes. The pistons took about 3 weeks iirc. I would of really liked something with a skirt coating like Manley but it just wasn't meant to be.
I did recently come across some Mahle big bore pistons with a 1.175" compression height that were made for Yates and the FR500C. The valve relief is for a 4v but that can be taken care of easily enough. I bought two sets of them, don't know why other than the price was right.
