Wes, Ed,
Great questions. Having spent 5 years living in Japan I saw a lot of
environmental destruction there. Junk yards on ocean front property had no
concept of what happened to the oil, coolant and gasoline that they drained
onto the ground, or burned along with electrical cable to get the plastic
coating off the wire. I saw a guy dipping PCB laden oil out of a
transformer and pouring it onto one of these fires. Their gasoline was
still leaded, at least up til I left in '92.
It's a funny place. Like here, it is illegal to modify the emission
controls on a street driven car. Yet there are shops everywhere who will
sell and install equipment which defeats or eliminates all these systems.
Go figure. If you are willing to pay enough money you can actually get a
car registered to allow it to keep these engine mods during the tough
Japanese Compulsory Inspection (JCI) process. This will get you hit with a
higher annual road tax, but it's easier than changing the car back to 100%
stock every two years.
The JCI process continues every two years, costing about $400 each time,
until the car is 10 years old. After the car is 10 years old it requires
annual inspection. This is why most cars are junked and crushed when
they're 10 years old. This is a gold mine for parts swappers. It also
provides an ample source of engine for replacement, should one actually wear
out in 10 years in a country where the "expressway" speed limit is 70 KPH.
In the case of rotary engines, these are almost always replaced with new
engines since Mazda (even in the US) finds it more cost effective to
replace, rather than rebuild these engines. Another odd problem in Japan is
that if you were to rebuild a 2000 cc engine and bore it 1 cc oversize you'd
push the car up into a much higher road tax bracket. (these are usually
$350-$800 annually)
As as emissions go the newer stock rotaries, with fuel injection and all
the other latest emission control devices is pretty clean running. You'll
also notice there isn't much exhaust volume coming out. I've been amazed to
see RX7's on cold mornings looking like they're barely breathing. My
exhaust is uncomfortable to stand in front of at a distance of less than a
couple feet at idle and has been known to blow fire balls so large that I
could see them in the rear view mirror! The restrictive stock exhaust
system keeps RX7's whisper quiet and helps them burn the fuel more completely.
Removing the stock exhaust and replacing it with a quality free flowing
system is good for a 22% power increase at 7000 RPM. (Racing Beat data.)
Mazda has used a variety of seal materials over the years and has reduced
the thickness and weight of the apex seals by nearly 50%. This reduces the
weight of the seals and the wear on the rotor housings, since these seals
are pressed against the rotor housing by centrifugal force when the engine
is running. Since '79 all the engines side housings have been gas nitrited
and wear quite well. I have worked on RX7's with over 225k on them that
were still going strong. My current engine has nearly 50K on it, and I
expect it to be able to keep going strong as an autocross engine for many
years. Nice thing about rotaries, as they wear out they get faster... then
the smoke starts, and pretty soon you can't see anything but big blue grey
clouds in your mirrors. The engines are still powerful when hurt like this,
but they may start using oil, coolant, and gasoline in equal portions.
Ouch! Piston ring to cylinder wear in a 4 cycle occurs at a rate of two
downward and two upward piston strokes per power stroke. The piston rings
have to endure a change in direction at the top and bottom of each stroke,
while the rotarys' seals are always traveling in the same direction. The
eccentric shaft rotates 1080 degrees for four cycles, as compared to only
720 in the piston engine. However, each time one apex seal travels 360
degrees around the inside of the rotor housing that rotor will have produced
three power strokes. These power strokes also exert pressure on the
eccentric shaft over 270 degrees of rotation, vs. 180 degrees with a piston
engine. The odd motion of the rotor inside the housing is the thing that
makes it seem like the seals will wear out quickly. The rotor is actually
traveling slower than the eccentric shaft is turning since the eccentric is
forcing the rotor to travel around a stationary gear on the side housing.
This gear mates to a larger gear which is pressed into one side of the
rotor. This is one of those things where a picture ie truely worth a
thousand words. I do have a program somewhere that has a working model of a
Wankel engine, but I don't know if I have any pictures that I could forward.
And finally, how do you verify engine displacement during teardown after a
record run? Opening up a rotary engine is a little more involved than
pulling a head. There's also no reason to have to tear one down. Measuring
the width of the rotor housings is all that's necessary to verify the
difference between a Mazda 10A, 12A and 13B, (982, 1146 & 1308 cc's)
although most folks who know these engines can tell them apart by eye, even
without the big molded numbers on the rotor housings. There is no way I
know of to increase the displacement of the engine, since this is all based
on standard size rotor housings. If you happen across a Curtis-Wright or
NSU Spider rotary engine you'd have to do a little researchbut their
displacement will be specified by the manufacturer somewhere.
Chuck
Pole Cat Hollow, NC
At 10:03 PM 12/3/1999 -0700, Wester S Potter wrote:
>Chuck,
>Everything I hear about Japan indicates an obsession with clean engines to
>the point that they replace engines rather than rebuild them. Where does
>the rotary fit in that scheme? I would assume the variety of domestic
>rotary engined models offered there would have to be quite good on
>emissions. What does Mazda do to make them comply? Have they changed the
>seals? The triple rotor motor has to wear on the walls of the block at a
>rate three times that of a four cycle engine If what I understand of the
>engines is right.
>Wes in SLC
At 9:49 PM 12/3/1999 -0700, Ed Van Scoy wrote:
Chuck;
2 (dumb?) questions:
If you add a muffler, does this create power-robbing back pressure?
How the heck do you verify displacement at teardown after a record run?
Ed
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