In October of 2008 I decided to tear
down my engine to replace the worn valve guides that I didn't replace
when I originally built up this engine. While it was down, we
found some issues from running the high compression (8.7:1 vs 7.0:1)
C-85 pistons that caused me to decide to downgrade the engine back to a
stock O-200. With the plane being down for a several weeks, I
decided this would be a good opportunity to build the new exhaust I've
been promising myself for several years. Additionally, with the
lower compression pistons, I hope to regain some of the lost horsepower
by building a much better breathing exhaust system.
All of the papers I have read say that the small Continentals don't
have enough valve overlap in the cam to take advantage of the
scavenging of a crossover exhaust system. Consequently, I decided
to make life a bit easier for myself by welding up 4 separate headers
using 1 1/2" mild steel pipes from the local muffler shop. Yeah,
I know they are heavy, but I can weld them with my torch and custom
build the whole unit in my hangar. I visited a low budget muffler
shop and had them bend up two 7' sticks of 1 1/2" tubing with a
total of 8 - 90 degree bends and 4 - 45 degree bends. I
bought a set of mild steel flanges from Aircraft Spruce, then
simply cut the pieces of pipe and welded them back together to build my
custom exhaust. Total cost , $100.
This is the old exhaust system that I build 12 years ago. It has
served me well and is still in good condition after 700+ flight hours,
but running a log down each side of a 4 cylinder engine is about as
poor breathing exhaust as one could design. This left side also
had a heat exchanger for cabin heat mounted on it.
Old right side exhaust. The heat exchanger here was used for carb heat.
Front view of old exhaust system.
New left side exhaust.
New right side exhaust.
Front view of new exhaust.
Finished exhaust with heat exchanger installed. In this
incarnation, the heat exchanger provides both carb heat and cabin heat.
Front view of my finished $100 custom exhaust system.
Later note: An improvement to this that I may make eventually
would be to sweep the pipes back parallel to the belly of the plane.
The stacks sticking out below the cowl creat unnecessary drag.