Hey TomH,

I'm a little confused about your post. In your first sentence, you say you have a YS 91 and near the end of the post you say you have a 91 Surpass. The difference between a YS91 and an "OS"91 Surpass are like trying to compare an apple to an orange. The power difference is incredible, especially if you have the YS 91 AC which has an air chamber on the rear if the motor between the carburetor and the cylinder that actually pressurizes the air / fuel mixture going into the engine which is similar to the way a supercharger works on a dragster. I had a kit built Sig Skybolt with an OS-91 Surpass on it and it was plenty of motor for the plane even though it was slightly on the heavy side since it was a kit. I also have a YS 91 AC on the front of a Great Planes Big Stick and it the only plane I've ever had that I would call overpowered and I rarely go over 1/2 throttle when I fly it. My YS has a 14x8 APC on it and I wouldn't use anything smaller that a 14 x 6. A YS 91 AC can turn a prop as big as a 14x10-14. A YS 91 in a Skybolt would be an AWESOME combination IMHO and I'm confident that you'd love it too.

A little trick that you may not be aware of if you have the YS is to wrap the fuel tank with reinforced packing tape BEFORE you put the foam around it so the pump doesn't split the tank. Now don't laugh at what I just typed. I have seen it happen with a YS 63 on a Mojo.

Good luck with your Skybolt and keep us posted on your airplane.................

Take care,
David