I’ve been searching the internet for a few days now looking for information on a whistle that attaches to a vehicles exhaust and sounds like a train. OK, I heard a lot of groans. Please forgive my intrusion on this site. I want to make one can’t afford to buy one. I’ve actually been working on some and now realize it may be a lot more shall I say detailed than I first thought. I can get a tone out of the ones I’ve made and realize the length of pipe is critical. I need to know the other critical dimensions. Any help, would be appreciated.
I have no idea what you’re talking about, but I wanted to say welcome to the forums. Hang around, and post often!
I’m afraid I know nothing about making whistles, for people or for trains or for car exhausts, but, like Cranberry, just wanted to welcome you to the forum. Perhaps we will all have cars sounding like trains if you get your question answered! 
There are people here who I am sure can help and they’ll eventually come by I’m sure.
Wooo! A train whistle! That sounds fun!
We have lots of engineers here . . . physicists . . . tinkerers . . . and I’ll bet one of them can help you!
If not, we can definitely help you develop a need to make noise on a smaller and more intimate level. I think I can do a train with a low D flute . . . DDDDDDDDDDDDDDD! Convincing, if I do say so myself . . . DddDDDDDDDDDD! Better if you get some d overtones in there . . .
Ever played a whistle, by the way? It’s incredibly easy . . . only 6 holes . . . here, let me show you . . . 
A friend of mine has a whistle that sounds like a train. He’s in a Bluegrass band, and he usually blows that whistle at some point in Orange Blossom Special. (Not being the fiddle player, he has lots of spare time during that particular tune.)
I never got a close look at it, but it sounded like it was really two whistles tuned just a hair apart. I can get a similar effect by blowing two whistles that aren’t quite together. Even better is playing F# (OOOOOO)on a low G and A (XXOOOO) on a high D when they aren’t perfectly in synch.
A quick trip to Google produced http://www.music.vt.edu/musicdictionary/textt/Trainwhistle.html where there is “A wooden whistle with three pitches producing the typical whistle sound of a steam locomotive.”
You can listen to it on that Web page.
Amazon.com has a variety (wood, plastic, metal) at http://www.amazon.com/gp/search.html/ref=xs_ap_sai1_xglna/104-6778026-4451931?index=mi&node=11965861&keywords=train%20whistle
It seems like you’d want a way to hinge it so that you could pull a wire, or something, and have it move up over the exhaust. In today’s high tech world, maybe it could be radio controlled.
My dad used to carve the wooden ones. I have one next to my computer.
I have pictures of what I’m trying to make and have a copy of the patent papers and drawings for one from 1912 (they have no dimensions though). I also have the on/off figured out. I need to know what the critical dimensions are. If I use .750" diameter copper tubing, what should the fipple(?) dimensions be and the angle for the air to impinge on it? those are the kinds of questions I need answered. THANKS!