PROBLEM ... I was given an engine cowl built to suit the O-200 engine but to fit it over the rocker covers I had to move it 4" forward as you can see in this first photo. So I knew I needed at least 4" but if I'm going to get an extension anyway would 4" be best or should I get a 6" one or even 8"? What would look the best and be more streamlined? "I feel the need for speed"
My first guess was 6". So I grabbed a length of steel pipe and a couple of these fittings from the local hardware. They are used for attaching fence posts onto concrete slabs. Luck would have it that the 2 drilled holes exactly matched the PCD of my prop flange and the larger circle fit nicely over the centre boss.
A half hour of hacking and hot metal gluing ( I wouldn't go so far as calling it welding for obvious reasons) and you have a mocked-up prop extension.
Here it is attached to the engine with the top cowl in place.
Here's another shot, this time without the cowl. As you can see I am using a length of rigid PVC conduit to test the curvature I need on the cowl. I think this is going to be really close. A bit of modification on the cowl, fill in the extra 2" at the front and it should SLICE through the air like an arrow ... well hoping so.
Here is what the real extension will look like. It is manufactured be Saber in the US.