I made it to 45 miles on the radargun with the "stock" engine after alot of experimenting. It was heavily modified though, port and polish, bigger carb, no head shims, new prop octura M445 (polished, sharpened and ballanced) reamed out and shorted header, and some mods to the hull and rudder.It was really screaming at the time, but now that I have met the wall with this engine I want to start over again with a different engine and see how much I can squeese out of it. There`s alot of relatively inexpensive and powerfull car engines out there that can be used once you have the correct collet and flywheel. If I see potentional with this STS, I think I will buy a Picco .28 P3 which is amongst the most powerfull car engines and try it out. Water-cooling isn`t actually neccessary as the cooling head will stick up enough to allow plenty of air running through it if the canopy is opened up a bit.
I have a video on our local forum, will try to link it in here

Here it is http://www.youtube.com/watch?v=z9yZFe9YggA

On this video I`m running a Just engines purple pipe, it is a very very quiet flatdisc pipe and you can se the carb (from a .91 aeroplane engine) But I sacrifice some miles to run quiet though. You can also see the rudder that has been cut/shaped and sharpened.

I think I`m around 42 miles here. Getting airborne at 5.30 min