LA Sleeves, 503(72mm) to 76mm Big Bore Sleeve, are around $115 each. If you upgrade your 503 Crank to 550F Big Bearing Rods, you could just use 550F(76MM) pistons. Still looking for a Piston to work with the stock 503 small bearing Rods. Blank 76mm Sleeves are MUCH cheaper. There is a guy who makes Porting Templates, but I haven't heard back from him yet.
I thought 503ULs used Bing 54, 36 mm carbs, or did you upgrade to 38mm bigger carbs?
I reread his letter to me. A guy who dynoed his 04 550F with 34mm carbs got 70hp at 69/7000rpms. Newer 550Fs come with only 30mm carbs, and I think I read, they make 58hp at 6800rpm. But I have read 58hp at 6500rpms also.
Actually, I just found a 94 Sled with a 500 Fan on Craigslist for $200 obo, I may eperiment with that 500 for a while. My 503UL on my plane was just rebuilt last fall, and only has 14hrs on it. Never thought then, to research some upgrades for the 503UL, I was looking at only 583, 617. 670, water cooled engines. I stll like the idea of the Big Dog, 629cc idea, (81mm x 61mm). Nice sleeper sled engine idea.
I can't believe a web site this big, and been around this long, and there is very little info on making any Custom Pipes, or Big Bores for these older 70/80/90s engines, or any Billet parts designed for these older engines. With 3D CAD programs cheap today. Alibre 3d is like $99, and they even have a CAM module. It's about $800, but free, if you know how, and where to look. I'm just learning this 3D stuff. I was working on 583/617/670 Billet Head idea with a CAD guy, but he has disappeared on me. So that Idea is on hold till I learn this better.
If we can get a stock 503 Port Map, or Trail Sport Port Map, you should be able to print it out, and tape/glue it onto a Blank Sleeve, and cut, or mill in, the ports yourself. This guy makes some, http://www.racelogic...hatissportport/ but his web site doesn't show any 503 or 550 Templates.