I have a friend that wants to run his Brodak 40 on muffler pressure.  I can't talk him out of this. Does anyone have any experience doing this?

Thanks for the response, I'll pass the information along.

Dubro makes a pressure fitting, drill and tap for 4/40. Fox makes one, smaller diameter hole, drill and tap for 2/56. I usually put it on the flat muffler extension but doubt that it makes much difference. OS tube mufflers have them in the muffler body itself. I think the Brodak tube itself is too thin to safely accept a pressure fitting. I would try it w/out muffler pressure first. If it runs fine and does not RPM upwind vs downwind you don't need one. Many engines are like that. If you do get significant run variation in windy conditions muffler pressure may help.

I have a friend that wants to run his Brodak 40 on muffler pressure.  I can't talk him out of this. Does anyone have any experience doing this?

Can't talk him out of it?  It's not a big life decision.  Switching to or from muffler pressure is easy and worth the experiment.  When I used to run Brodak 40s unpressured I would get a distinct richening when headed upwind (losing power into the wind) and leaning when headed downwind (gaining power with the wind) even in moderate wind, similar to Brian's experience with his Chipmunk.  This is just the opposite of what we would want to happen even if we wanted the engine to change speed twice a lap, which we don't, at least I don't.

I agree with Pete that the wall of the stock Brodak muffler tube is too thin to drill/tap.  There is a double wall thickness where the front and back halves of the muffler tube join, and I've had good luck locating the pressure fitting there.  The flat "header" part of the muffler is probably a better and easier place to drill and tap.  I don't think the location makes any performance difference, as the pressure is positive throughout the exhaust system.  I have even seen engines without mufflers pressurized successfully by locating the pressure fitting in the exhaust stack of the engine.

I've had really good results flying several Brodak 40s, both the early and late versions.  I like the fact that with its light muffler it weighs almost the same as the OS20FP with its heavy muffler, while providing twice the displacement.  

Tell your friend good luck with it.  

If you get too much rpm variation, try lower pitch props. I use 11x4 thunder tiger prop and the motor never cares if it's windy or not

While I like muffler pressure, there is an alternative fix for the rich/lean crap in the wind. Just hook a hose from the uniflow inlet to a non-pressurized area inside the cowl, such as in the backplate cavity. Brett says that's his sekrit trick for windy conditions, but there's no reason I can see not to run it this way all the time.  Steve