[Sci-Fi]

Without upgrading the rods and pistons, I wouldn't add any more boost. You are asking for bent rods or worst, a thrown rod through the block.

A pulley change (smaller) will add boost, BUT you need to know if you can tune the computer to add the proper amount of fuel to take advantage of it. If your Whipple is running fine and has been for years, then knock on wood and be happy with what you have. No need to cause a problem that may not have an easy solution or are unable to return back to where you started.