exhaust (trails) on a B25 Mitchell?

I`m pretty sure all those "lumps" are exhaust ports. Your best bet is looking for some reference pictures and go from there. I`m not exactly sure of how the staining would occur but I`m sure someone will be along soon to straighten us both out...lol.

Len

http://www.flickr.com/photos/shawnmanny/sets/72157624942864420/

maybe these will help

I do not believe the bumps to be exhaust ports, just vents. On the "J" model(?), the exhaust stacks stick out through the cowl flaps about midway up the side. (same for the "D", the "B" comes out further down)

Yankee Warrior - "D"

"J"

You want B-25 exhaust trails?

I don’t like citing one model as a reference for another, but this looks extremely similar to your build:

Kermit: Those are exhaust stacks, ports or whatever you want to call them. There are fourteen of them, one for each cylender. The ones you see with a single exhaust are probably late conversions. I plan on exhaust staining mine the same way I would any other exhaust.

Aaaah

So there should be a trail coming from each port there and accumulating in a big stream on the sides of the nacelles and top of the wings as i figured it...

Gonna work on that as soon as i am done working today. Thanks alot guys! You rock

Richard

B-25B's, C's, and early D's were built with single exhaust stacks on the outer side of the cowls.  Because the flame was visible at night to the bad guys, single stacks were put on each cylinder on all following B-25's, which created a lot of noise in the cockpit.  The story was you could always tell a B-25 pilot because he couldn't hear.  After the war many were modified with a collector ring on the rear row going to a single outlet, or all cylinders going to a single outlet.  They were used as trainers or transports then and the flame didn't matter.

I would expect that the exhaust staining might be less apparent with the separate stacks because it was spread over more of the cowl and nacelle.  The same amount of soot and oil, just spread thinner.  Studying photos is always good.

I've got a couple good shots of the nacelles from B-25's at the 2010 Dolittle Reunion. They are warbirds and are kept really clean, so they are not going to show the grime that a wartime bird might have shown.  None the less, I hope they can help you a little bit.  Rick.

Those bumps are very definitely fairings over individual exhaust stacks, which is the correct configuraton for a war-time B-25. Most of the Mtichells flying today have been converted to the later TB-25 configuration, which uses a collector ring and single exhaust stack outboard, but they still retain the individual stacks on the inboard side. A lot of this had to do with getting carburetor heat, as the wartime birds simply opened a scoop on the top of the nacelle behind the two top stacks. This sure ducted warm air into the carbs, but it was a little shy on oxygen, so the resultant power loss was enormous. With the collector ring and the stack, carb heat could be obtained in a more traditional way with a muff over the exhaust pipe to heat ambient air. In any event, great looking build so far!!

Ok, this may be a little overboard but, I've got some good comparative photos and Ashley has the knowledge to explain them.  Here are some examples of different exhaust configurations.  Mr. Ashley give us the lowdown.

Here are two details of the late D and on production exhaust.

Great illustrations John.  Thanks for the info.   Rick

jeaton01

...which created a lot of noise in the cockpit.  The story was you could always tell a B-25 pilot because he couldn't hear. 

Actually, the story was that you could tell which one was a B-25 co-pilot and which was a pilot by which ear they were deaf in...  The pilots would usually keep the "inside" ear uncovered with the headset so they could talk to each without using the ICS. Pilots would be deaf in the right ear, co-pilots in the left...

This practice was reflected well in the cockpit scenes of "The Ruptured Duck" in Thirty Seconds Over Tokyo...