I came up with a plan onmeasuring the fuel consumption with the new
ignition using the RX8. The idea is to take the ignition trigger out
of the RX8 computer and transform it to fire the plugs six times
instead of only once. Then replacing the Kettering smart coils with
four of my ignitions.

This is a daunting chore if done over a wide range of RPM's but
rather simple if only one RPM is involved.

4000 RPM in top gear is 80 MPH so I chose that RPM. This will use the
recorded  OBD II combustion air flow data to calculatethe fuel burn
with one spark and six sparks.

See the attached  OBD data jpg.

The idea is to use 4 double pole double throw relays to select one
spark or six sparks while the engine is running. This way the engine
can be started on one spark and accelerated up to 4000 RPM and 80 MPH
on a flatroad.

Then six sparks are selected with the relays and data is recorded.
Back to back tests under the same atmospheric conditions, the same
RPM and the same engine load can be made every few minutes to detect
small changes in fuel consumption.

The attached schematic is for one ignition and one plug. This will be
reproduced for 4 spark plugs.

Please upload your comments and any better ideas.

Paul Lamar



I hope you have access to an old airfield or something (maybe the
ones that the Myth-busters use). I routinely monitor my fuel
consumption at the g/hr rate on the interstate and I find it
challenging to maintain any sort of constant burn rate. Any change in
speed is going to cause your measurement to be invalid unless you can
duplicate the same event during the base test.. What about an hour of
dyno time at a local tuner shop?

Daniel Tyler


We have this 300 mile long highway here in California Route 5 when at
certain times of the night and on certain days there is very little
traffic. Dead flat and dead straight.

Also the beauty of OBD  II it only takes about a minute to get a good
sample of fuel burn.  The raw  data is updated about every two
seconds and the sensors are superb. It does not use fuel flow sensors
which are historically unreliable. It uses the mass air flow sensor
and then injects the amount of fuel needed. The computer knows how
much fuel is being injected as it reads the O2 sensors to verify the
mixture ratio.

Chassis dyno's are not accurate (OK for HP) and engine dyno's are
$600 a day and up. Mostly up.


Paul Lamar

     If you say: 'Fuel economy', instead of: 'Fuel consumption', it can be of help to
    you feel good, anyway, in a Broadway show, they said: 'I'm feeling too good today'
       Have a good day. Best regards. Salud †

                Jose Gros-Aymerich
                  Madrid, Spain


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