All you RX8 owners that live in states that allow
you to improve your engine I think you can get better
miles to the gallon by using MSD coils.

If so measure the gas mileage before and after.

The most accurate way is get a OBD II software and
USB cable for a notebook computer.

That will give you the mass airflow every second and record
it on the hard disks.

Then set the cruise control to 60, 65, 70, 75, and 80

When you are getting better MPG the mass airflow will
go down for steady speeds. You will know this right
away.

My theory is these MSD coils will help greatly in
those speed ranges.

Paul Lamar

I've kept track of every tankful of gas that I've put in the car
since I bought it in 2003, and have a spreadsheet of all the
mileage data.  About 6 months ago, my average went from 17-20
mpg, to a minimum of 22 miles per gallon for every tank! And was
climbing slightly every tankful until I changed the coils. My
highest was the week before I changed the coils...24.7 mpg. Same
gas, same station, almost always the same pump. Only the price
keeps changing!

Since I put the new coils in, the last three tank fulls have been
18.5, 19.1 and 18.2! I calculate it by using the amount of gas
reported on the pump when I fill it (I fill it up every time I
get gas) and the mileage on the trip indicator, which I then
reset.  After 65,000 miles odometer indicated, the total in my
spreadsheet is within 100 miles.

Harley

Very interesting.
If this proves to be true in the long term my guess is Mazda
changed the primary winding to cool the new 100 B coils. The
effect of this is less spark energy I suspect. I can check this
perhaps on the test bench as I have both the early coils and the
new 100 B coils. If that proves to be true that is a bit of
evidences that more spark energy over a longer period of
time  will improve the BSFC. Something I have suspected
about the rotary moving combustion chamber for a long time.
The MSD coils come closer to this ideal than anything I
have seen so far.

http://www.rotaryeng.net/Why-CDI.html

When you fill up Harley you should make
a note of the OAT temperature. Fuel expands and contracts
with temperature and I don't think the gas station pump can
compensate for that. I think the gas station flow meter just
knows the gallons and not the pounds of fuel.  Another factor
is the percentage of alcohol in the fuel. Since alcohol gives
less energy per gallon that too affects the MPG. Since it has
been steadily getting colder up there I think you were getting
more energy in your tank up until the time you changed the coils
to the 100 B.

When I first got the RX8 in 2004 I did the OBD II trick and saw 25
mpg  at a steady 65 MPH. If you know the mass airflow and the
mixture  ratio you can calculated the pounds of fuel going into the engine.

The on board computer is very good keeping this ratio at 14.7
pounds  of air for every pound of fuel. It is called the equivalence
ratio or  Lambda in this spread sheet of OBD II data. 1 Lambda is 14.7:1.
If I am using 3.6 pounds of air per minute I am using .245 pounds
of fuel per minute. That is 14.69 pounds per hour. So I am going
65 miles on 14.69 pounds of fuel. At a fuel weight of 6.25 pounds
per gallon that is 2.35 gallons an hour or 27.66 MPG!

The excessive fuel consumption of the rotary is an urban
myth perpetrated by lead foots. If you use all the 250 HP
you are going to burn the fuel.

Notice the weight of a gallon of fuel varies according
to the temperature. One must also pick a flat road on
a windless day near sea level.

This is a very accurate way of measuring the steady speed
fuel consumption. It is the way some cars are able to display
the MPG in real time on the instrument panel.

Just about any OBD II software that runs in a note book
computer will work.

Paul Lamar

Spark-current-LS1-V-MSD.jpg indicates the duration of spark from
the LS1  coil is greater than that of the MSD coil, although the MSD
coil has  greater energy, it is expended in a shorter time.  While
the MSD spec  says spark duration is 1.2 ms, their graph indicates
1.0 ms.  Whether the greater energy or the longer duration is of
more value is  probably a question that can only be answered by testing.

Victor

Thanks Victor. As always your messages are insightful.

BTW On my list of things to do is build a CD ignition system
that fires every 10 degrees for 40 e-shaft degrees or so.
Unlike a piston engine the mixture in a rotary is
in close contact with the plugs for at least that long.
The expansion stroke is 270 degrees rather than 90 in a
piston engine. At 3000 RPM one rotation takes 20 ms
so expansion time is at least 15 ms so 1.5 ms is hardly
adequate IMHO. 3000 RPM is the cruising speed of an
RX8 car.

At high RPM the rich mixture is thrown out towards the
plugs. One reason the rotary  will run leaner than a
piston engine.

Paul Lamar

A sparkplug that will spark for each 10 deg, or in a series along a
specific degrees of an engines rotation will be very beneficiary, but
only in the start up sequence. Once it is running, only a very specific
ignition point will do.

The optimum condition sought after, is when the charge has reached
it's  burn peak pressure at the time of the engines  highest compression
position.

The flame front in gasoline  is so slow, that ignition spark has
to be  administered well before peak compression position, in order
for the gas  to reach it's own higest burn pressure to coincide with
that point. (  that is our famous "advanced timing").

The time when the engine moves towards it's higest mechanical
compression point, and at the same time, the gasoline is burning
and  busy expanding to it's peak pressure, is wasted energy, where
the engine  has to move against a continous build up of pressure.

Another spark 10 deg after, is going to be a waste spark, and do
nothing, but if instead , another spark could be administered
simultaneously at another location, the expanding  burning gasoline
sphere each sparkplug is responsible for igniting, will be travelling
lesser distance , than one single sphere caused by one sparkplug.

Thus shorter time can be achieved to reach peak pressure and thus
advanced timing can be set closer to peak compression position, (
or in  pistons..TDC), thus lesser back pressure in the compression stroke.

Downside is a possibility of knock, when two flame fronts are expanding
from two different positions in the combustion chamber, and the
travelling shockwave is compressing unburned gas/air mix in front
of it,  this however usually not an issue, airplane engines and many
car engines  have double spark plugs.

Another way to cheat the backpressure in the compression stroke is
to  introduce an aromatic like Acetone, (If you have a compsite
aircraft,  stay out of that)  or Hydroxy gas.

The idea behind the Hydrogen generators sold and installed, ( lot
of  hype and lot of scams, and a lot of overinflated numbers....but
they do  actually work though) is to have a hydrogen cell that will
run out of  the alternators pull, thus produce hydrogen and oxygen..
Typically they  pull about 20 Amps, so that is around a half of a
horsepower, they ( the  good ones) can typically produce about 1.5
to 2 liter /min.

A normal soccer moms van, a 3 liter V6 ...typical,... that runs in
freeway speed will run in maybe 3000 RPM, and thus exchange 1500 liter
of gas through that engine every minute, that pretty much shows
that the  Hydrogen ( in this application) is not a fuel,...... 1.5
liter against
1.5 cubic meter....one tenth of one percent in volume.

The way it acts is to treat the back pressure during the build up.

Hydrogen and Oxygen ( Hydroxy) have a flame front of 10.000 ft/sec.
Probably one of the highest flame fronts amongst explosives, not many
things will beat it.

Hydrogen, the smallest existing atom, will in comparison with fuel
particles, be like Hindenburg and Hydrogen will be like indians
everywhere shooting fire arrows on the blimps, setting the
whole Hindenburg on  fire...(...-" Oh the humanity"....,) quicker than
quick. Gasoline is still the fuel, Hydrogen is merely the firestarter.
Gasoline will still burn slow, but we will get close to
simultaneous  start of the fire.

Here we come back to the topic again, thus, we will be able to retard
the advance timing for a lesser pump loss during the compression
stroke.  Many that run Hydroxy set the advance timing to 10 or 15 deg.
(the exact point will only be known in a dynamometer though)

So either way it is done, with added components, like Hydroxy, or
Acetone, or with a very strong spark that will really get the  fireball
going ( preferebaly with a pretty good shockwave in the beginning,
to  cover a bigger initial ignition volume) , or with multiple
points of  ignition, or a combination of applications,  is a matter
of choice and  method, as long as the air/fuel mix is put on fire,
and are given the  opportunity to build up to it's peak pressure as
soon as ever possible,
( and at the same time get no knocks) , and be able to start andcomplete the process as close to TDC as possible.

Anything that will help avoid as much as possible the backpressure
building up during the compression stroke, will be beneficial.

I have never seen a four or six spark plug engine, that would be a
kicker, placed in such a way that they strategically cover the
floor so  to say, each one simultaneoulsy fired with a snappy spark.

A rotary will, by it's basic design, lend itself to that much
better,  than a piston engine where the valves are competing with space.

Roger

Paul,After reading Roger's post about multiple flame fronts I got
to wondering if you know what ignition advance Axiro uses with their
side by side plug arrangement aircraft engine. Is there a link for a
service manual for that engine as used in a sailplane?

george grimes

No I don't  but perhaps Poul Woelfle will tell us as he is on here.

Poul Henrik Woelfle AIXRO <ph.woelfle@woelfle-engineering.com

Paul Lamar

Paul,

To go alnog with George's query, do you know what the timing of the 26B Le
Mans three plugs was?

Dale Davies

You got me there again. I don't think it was mentioned in
the Le mans paper. Most of the racers run fixed 22 degrees BTDC.

At low manifold pressure low power 3200 RPM the
RX8 goes as high as 44 degrees BTDC. It seems to vary
a lot 36.5 to 44.

Paul Lamar