Assembling the ductwork and
exhaust on my Subaru 360
April 1, 2009: What to do first? At least I can assemble
exhaust and duct-work parts I have lying about. I understand that
the Subaru 360's engine performance is closely tied to the amount of
"back-pressure", that is, the resistance the exhaust gasses meet when
exiting the motor. It needs a certain amount of back pressure -
it presumably won't run as well if there was no prechamber and muffler
bolted on. SO THEN...
Having learned that the "correct" color for the inside of the engine
bay is "body color", I scrubbed and painted the end of the bay where
the parts would go. I also wire-brushed and painted the bits
involved - the pre-chamber, the air filter can, the two ends of the air
intake duct. I soaked all the rubber parts in armor-all for a day
part of the duct, in the "paint shop"
pre-chamber, ready to install
To help prevent an exhaust
leak, I used
"Permatex Red gasket maker" on both sides of the stock steel doughnut
that will go between the pre-chamber with the muffler. An
off-label use, for sure. It should be good to 650
degrees - we'll see if it helps here.
duct-work, complete with cleaned up stock straps on the rubber,
and new foam insulation where the duct meets the body, in place
As the Subaru 360 has no exhaust valves that determine when the exhaust
gasses are allowed to escape the cylinders, something else has
Here is what the Subaru
360 Driver's Club "Book of Reprints" says about
the exhaust system.
If that's not enough, here's a detailed
article on back pressure
And if THAT'S not enough, here is a cool animation that shows the
effect of back pressure
(or the "rebounding shock wave") in the expansion chamber
Note the green "good gas" trying to escape out the exhaust, and getting
pushed back into the cylinder via back pressure...
Here is the engine bay with the muffler, pre-chamber and air filter can
installed. I will install the cowling after I am sure it's