Will the engine run "OK" with only one plug per rotor firing?  How
 convenient of Mazda to include two spark plugs.

 Matt Naiva

 It will but the power out depends on which
 plug. The top plug you may hardly notice
 the lower plug you will have a significant power loss.

 You need to change the old type plugs every 50 hours.
 Rotaries fire twice as often per rev than
 a piston engine. At a given prop RPM four times
 as often as a 2500 RPM direct drive aircraft
 engine. Now this is for the old style metal plugs.

 The plugs in my RX8 are Iridium and we have no
 data on the life of these plugs in aircraft service.
 A car cruises at 3000 RPM on the freeway so it might
 be half as long as the rotary. I have 30,000 miles
 on the plugs I have in there now. At an avg. speed of
 60 MPH that is 500 hours. However it is unlikely they
 will last 25 hours in aircraft service.

 I also notice they are charging a lot of money for these
 plugs.

 Paul Lamar


Hi Paul,
I take it you mean the lower(leading) plug firing, you will not notice a
difference. The upper plug (trailing) firing will contribute to a
noticeable
power loss.

Dale Davies


I said it right.
The leading plug (lower) you WILL notice a difference.
The top plug  (trailing) you may not notice a difference.

You can see it in this picture. The top hole (trailing) is very small
with the plug mostly shrouded.  This is why it is not all that effective in
firing the mixture on its own. It is mainly there to fire the residual
un burned hydro carbons that have not burned because of the squish
effect.

The hole must be small as some of the compression pressure will be lost
to a leak as the apex seal passes over it.

Note my invention back in 1975 :)

Paul Lamar


Has anyone considered using a slot in parallel to the apex, instead of a
small hole for the top plug?

Ed Carver

Not that I am aware of.

Paul Lamar