12.4 Exhaust Installation

This entry is part 32 of 50 in the series 12 - Engine / Propeller

I’ve never liked the factory supplied exhaust. It amounts to 6 individual pipes (three on each side). The middle pipe on each side is straight. The forward and rear pipe on each side have a bend so that they each exit the bottom of the cowl directly adjacent the middle pipe. Not only does it result in a larger opening in the cowl, but recent flight tests by other builders have determined that the exhaust exiting perpendicular to the outside airflow generates drag which results in a loss of airspeed.

My original plan was to obtain a set a exhaust headers from an old Cirrus. Mooney or other IO550N aircraft.

I was thinking that I could reverse the direction and then they would exit the cowl pointing back. But A) I wouldn’t find any affordable headers and B) my rough calculations showed they wouldn’t inside the cowling. Having custom exhaust headers was WAY too expensive.

Then another builder (Scott Derrick) told me about Clinton Anderson at Custom Aircraft. I sent Clinton the dimensions that I wanted and he whipped up a pair of custom exhaust headers at about a quarter what I was looking at for used Cirrus headers (which would have still required significant modifications).

Within a week, I had my new headers (with an oil breather line plumbed too).

The left side header is a little longer since it sits forward of the right side. Because of the slope of the cowling, it has to be longer to exit the cowl.

Then I installed the lower cowling and marked the location where the exhaust would be penetrating the lower cowl with green tape.


Then cut the initial holes for each side (a little smaller than necessary. After that, it was raise the cowl, see where it contacts the exhaust, trim away some of the cowling around the exhaust, raise the cowling, see where it contacts the exhaust, trim away some of the cowling around the exhaust, raise the cowling, etc., etc., etc.

Eventually, I was able to install the lower cowling with the exhaust outlet extending beyond the cowling.

Left Side

Right Side (on the inside view, you can see where the breather tube will dump into the exhaust)

My next task here will be to create a fairing in front of the exhaust to streamline the airflow around the exhaust outlet.


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