We got the plane up in the air again, there was gobs of power,
the temps stayed low, no higher than 160 for oil and coolant,
but CO in the cockpit reached 300 PPM so it was only one circuit
of the traffic pattern and a smooth landing. That SS flex
exhaust tube is getting replaced tomorrow with the inconel. Also
going to make sure the firewall is well caulked.


At full throttle the engine is missing a bit, I think it's too
rich. The pilot was going to play around with it a bit but due
to imminent danger of CO poisoning he decided to land it. I'll
take it up on the next flight after some Van's familiarization
flights and exhaust refit.

I'm using the stock 13BREW O2 sensor, Tracy- is that the one
recommended for the EM2? It seems that the EM2 mixture graph
shows about 3/4 rich, so I lean it out slooooowly, and it
doesn't have a sweet spot- it just goes to about 1/3 scale.
There seems to be no in-between.


But, the plane flies nicely, like an RV should.

Next flights will be in a few days.

Brian Trubee

I don't think it is the flex tube. I just installed some
in the race car.

I think you have a low pressure in the cockpit.

Paul Lamar

     One of the connections to where the tube connected to the
muffler showed a lot of leakage. I'm going with either inconel,
or 321. Still, I don't like the thought of the thin gauge of
metal used for the flex tube, given the exhaust heat.  I have
some Inconel bends, I'll see if I have enough to fit it up, or I
will cover the flex tubes in fiberglass to fix it's unique shape
and positioning, and them use them as a model for a muffler shop
to create some new ones out of 321 stainless.

So, the exhaust problem and the tuning issues are the only real
squawks at this point. The engine cools just fine.
     One of the connections to where the tube connected to the
muffler showed a lot of leakage. I'm going with either inconel,
or 321. Still, I don't like the thought of the thin gauge of
metal used for the flex tube, given the exhaust heat.  I have
some Inconel bends, I'll see if I have enough to fit it up, or I
will cover the flex tubes in fiberglass to fix it's unique shape
and positioning, and them use them as a model for a muffler shop
to create some new ones out of 321 stainless.

So, the exhaust problem and the tuning issues are the only real
squawks at this point. The engine cools just fine.



Brian Trubee

Check out JC Whitney or Warshawsky.
I just bought some SS braided exhaust flex tube  10" long for the race
car muffler for $30. Works great and is widely used on
transverse engine front drive cars.

The exhaust comes out under the wing root which is a high
pressure area. If there is any leakage into the cockpit
that is how the CO can get there. Most RV have open areas
there to get the fuel lines and spars inside the cockpit.

Paul Lamar


I just finished welding up my exhaust system, I had to wait
until I got the inconel filler rod to finish it up. I'll get
some photos of it installed later today after I get up to the
hangar and put it on the plane. It attaches with V-band clamps
to the 1' headers coming off the engine. The headers are .125
308 stainless. The muffler is hung under the fuselage with
stainless straps that give it plenty of movement. So, between
the bellows and the flexible muffler mount, I'm pretty confident
that I will not get any failures due to excessive rigidity of
the system.

Brian Trubee

I inserted the last previous message on the subject to give some context
to your new message Brian. I see you have bellows in there.
I have used those before in an exhaust system I built for a boat.
They seemed to be reliable however it was a cooler exhaust diesel
engine. In theory they could crack and leak so I would keep an
eye on it.

 Way back in the early days of the British Mini, the first
transverse front drive car, they had a lot of trouble with
exhaust cracking as the engine rocked back and fourth on its
crankshaft axis while the exhaust pipe had to go back under the
car at a 90 degree angle.

The universal flex stuff they now use in front drive transverse engine
cars is quadrupole braided stainless steel flex pipe.

http://www.truckmod.com/directpart.asp?vencode=V32&partnumber=4258

I just used a piece of it on Brian Linn's race car exhaust system.
No problems with it. Worked great.

Therefor braided flex is what I recommend.

Paul Lamar

Here   is the exhaust system on the plane, without the heat
shielding. The bellows are made from 625 Inconel, so I think
they should hold up. I'll put some temperature sensors in the
engine bay to monitor temps in the cowl.

Brian Trubee