Overshoe wrote:Ian, don't worry about the freeware version. It is worth every penny. I'll be waiting for yours.
I second Tom! Any tier 4 is great! If you're looking for reference photos, here are some that may help depending on what Tier 4 you are doing. CSX, Demo, BNSF's ET44C4 with A-1-A trucks, CN, or UP. (not mine):
Demo:


Early rollout (CSX, CN, UP, & BNSF, with the swoosh logo on the side being smaller):


Late rollout (NS; note the exhaust area in front of the radiators being slanted down, with the addition of the cab headlights of the ES44AC):

Hope these helped. Good luck on your project! I'm happy to provide you with an ET44AC horn if you want.
