I have a quick question, what Air Horn was used on the NS Dash 8-40CW's.
Thanks in Advance
The C40-8W's were delivered to Conrail with the standard Leslie RS-3L. Most former Conrail locomotives still retain this horn, although it's not uncommon to see...er...hear this horn on other NS locomotives due to horn swapping (e.g. a malfunctioning K5LA on a Dash 9 gets replaced with an RS-3L).
Here are a few links that might be useful to you...
Leslie SuperTyfon at Trainhorns.net (http://trainhorns.net/leslie/supertyfon.html)
Leslie S-3L at Five Chime Consultants (http://atsf.railfan.net/airhorns/s3l.html)
Also, almost all of the C40-8W's in the 8420-8449 number series I've heard have P3's, but I don't think they were delivered with them.