Just a note about peripheral exhaust ports and apex seals.  Note
that

Mazda has

only built exhaust ports up to a certain width - no wider.
There is a

reason for this -

if the port was wider there would not be enough support for the
HOT

apex seal.  The

seal would become concave and actually extend into the exhaust
port and

break

when the upper lip of the port was crossed.  This probably
happens a

little right now

but not enough to be harmful.  Two stroke motorcyles use a
'verticle

bridge' in the

center of the port to give the piston rings support.
Unfortunately,

this can not be

done on a wankel due to the hot exhaust gases would warp or
destroy the

bidge.

Ken Powell

Can Ken or someone help me understand this?  I thought the rotary
had higher exhaust temps due to not having exhaust valves to absorb
some of the heat from the hot exhaust gasses.  Like the rotary,
two-strokes don't have any exhaust valves either, and both burn
pre-mix gasoline, so why would the rotary have higher exhaust temps
than a 2-stroke?

That could be partly the reason. I don't think anybody has precise
data on what parts of the increased heat are the result of any one
particular factor. We do know the exhaust is hotter. We do know there
is excess unburned fuel in the PP exhaust. We also know the peripheral
exhaust port opens sooner than it could. When we get data on the RX8
engine we will know more.

In other words I don't think we know.

Paul Lamar

   I would like to try to answer this as I understand it.  The wankel has high exhaust
PIPE temps because the charge does not burn completely in the combustion
chamber and completes the burn in the exhaust pipe, which cause very high
exhaust gas temps.  I have never heard that the combustion chamber temps are
excessively high.  What about this Paul?  It seems that the combustion chamber
temps would be lower due to the larger wetted area of the rotor and the rotor
housing and that this is one of the reasons that the wankel has problems obtaining
low bsfc (but boy, Tracy is sure proving this to be an 'ole wives tale').

   I am a little more confident dealing with the 2-stroke - lots of experience here.
Remember that a 2-stroke fires every time the piston cycles - this gives the piston,
rings, and spark plug less TIME to disipate the heat from combustion.  If the 2-
stroke were to obtain the hot combustion chamber temps that a 4-stroke sees, the
piston crown would (and will) melt in short order.  Ask me how I know this!  Since
the 2-stroke has less time to disipate the heat, cooler combustion temps are
required to keep the temps of the piston lower.  Thus, a 2-stroke sees a bsfc as rich
as .65 to keep the temps in check and should never see an egt higher than 1200
degrees.  A  typical cruise egt is 1050 degrees with a max of 1150 if you want long
engine life.  If you lean a 2-stroke to far while under load you will either seize or hole
the piston.

Ken Powell

 
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