Steve,
 As Paul and many others among our group have said, many thanks for
 sharing
 your wealth of experience with rotary installations. Can't beat hands on
 experience. Getting back to the CDI vs Conventional ignition, the rotary
 is a unique case because the spark plugs can't protrude into the chamber
 at all. Since the sliding seals prevent that I would think that a plug
 that presented the electrodes as close as possible would be best. I read
 that VW was experimenting with a no-side-wire plug and apointedprojection
 on the piston to fire to. I don't know if they ever used it inproduction.
 The spark actually jumped to the piston. I thought that this typeofsystem
 would be perfect for the rotary. The plug could be closer to the rotor
 without a side wire and the long spark would be perfect to ignite the
 lean mixture. Having the plug closer would even bump the compression a
 little. Just thinking out loud but it seems like a possibility.
 Bill Jepson

 We always removed the spark plug washer to move the plug closer.
 Works great. There are washers available from Mazda.

 Skip

 Skip did you use no washer or the substitute washer from Mazda Any
 measurable difference in performance or other, such as different carbon
 patterns on rotor at disassembly

 Steve Beckham

 Steve, We took the washer off. It was a drag race application. The gain
 was only measurable at the track clocks. We thought we had a secret
 performance gain, then we found that Mazda Speed offers washers to
 move the plug in or out.

 Skip

 Steve, I'd like to say some more about the spark plug issue. The
 sparkplug
 washer trick did not have any effect on charged cooled rotaries. In fact
 is was a negative effect. Don't know why that was. What did work is we
 changed from a 14mm spark plug to a 10mm spark plug and gained some real
 hp and torque. Ten to twelve hp on a single rotor. There is a serious
 leak when the apex seal goes over the hole or any hole in the
 rotorhousing.
 So the smaller the hole the better. I'd like to reduce the Mazda. I don't
 know why they don't. Just about every mfg has gone to a smaller
 sparkplug.

 Skip
 -

 That is only for the trailing plug Skip.
 There must have been something else going on with the Rotamax.

 Paul Lamar

 Thanks Skip...no doubt about the factor of the apex seal going by the
 spark
 plugs.I remember at some point one of the Mazda factory guys in the early
 1990's telling us they dealt with this factor when they did the three
 sparkplug modification for the four rotor LeMans project.They were using
 castings with an additional sparkplug above the two original
 sparkplugs to
 address the highly quenched trailing end and its poor flame propagation,
 they made the plug hole as small as possible.It demonstrably worked to
 address fuel consumption byburning some of the fuel that was before
 simply
 going out the exhaust pipe.

 But having said that, the leakage was clearly
 evident because while it actually improved fuel consumption, the
 volumetric
 efficiency of the engine dropped according to the Mazda folks.About the
 simplest way they addressed the high-to-low pressure area flow was to
 keep
 the plug hole as small as possible.For our application of the engine to
 sustained high power settings involved in aircraft use, at this point in
 development and using proven technologies, it seems the three sparkplug
 approach with this small hole would work well to substantively address
 the
 issue of this highly inefficient and quenched area in the combustion
 chamber.

 But Mazda is driven by the automotive production market and it is
 clear they ran the numbers and more cost-effective to develop the two
 sparkplug side port RX-8 to reduce the overlap and improve BSFC for road
 cars.Just wonder whether deep in the bowels of Hiroshima whether a group
 of people have, or arepresently working to save this little engine by
 experimenting with more than one option, includingUncle Paul's turbo
 compound ideas.If not, it is because their hands are tied financially by
 short term cash flow and profitabilitythreatening car companies.The
 Mazda organization has some amazing, smart folks who remain inspired by
 their rotary "father", then later Mazda Chairman Yamamoto.It seems they
 must have already, or are currently exploring the TC option to see
 what it
 could hold for this little engine by putting to work that unusually high
 amount of energy going out the exhaust pipe.

 Meanwhile, absent any major
 changes in design, we know a three sparkplug approach works to improve
 the
 burn and improve fuel mileage.Yasuo Tatsutomi told Yoshinori Honiden they
 had to reduce fuel consumption 10-15% to win LeMans with an rpm band that
 could range from 6,000-9,000.To do that with a standard, homogenous
 charge
 engine is like climbing Mt. Everest. They simply could not have done it
 without those rotor housings.Even with them, the LeMans drivers had
 strict
 orders from Yoshinori Honiden to lift and early/coast at the end of the
 straight and soft pedal through the corners. The primary goal was fuel
 savings but it was also easier on the engine heat flux.In this respect
 they even went from black to silver paint on the upper engine cowlto
 address temperature issues.

 The previous year the ceramic exfoliated inside
 the engines. Aircraft race duty cyle is harder--no lifting at the end of
 the straight stretch and going into corners-- and we are attempting to do
 that using what are basically warmed over, off-the-shelf production parts
 for grocery getters.That is a serious challange no matter how we slice
 it.
 But in the words of Nobuhiro Yamamoto (he headed up the third gen RX-7
 engine development),after the LeMans effort,"We can no longer say we
 share major components between the production and racing rotaries.But we
 are still a very close bunch--the rotary people!"A rotary brother indeed.

 -
 Steve Beckham

 Steve,
 I seems to me that the idea to use a small plug would be very"doable".
 Filling the spark plug hole and using the 10mm plugs to keep everything
 tighter to the chamber seems like a good idea. Motorcycles have been
 using the "little" spark plugs for years sothey are available. Using
 10mm plugs would also be a better way to add the far trailing plug.
 I think using the standard housings and trying to do the milled side
 plates, (all steel nitrided),and staying with all p-port will get us
 closest to the proper aircraft configuration.
 Bill Jepson

 I understand that a flush (or nearly so) spark plug was tried but that
 the
 problem with it was carbon trace arcing/shorting.Could a plug be designed
 that was truly flush with the housing surface which was kept clean by the
 passage of the apex seal - eliminating any carbon buildup?The
 sealing/insulating material would have to be designed to be cut/eroded by
 the apex seal, and not cause the seal any damage.

 Matt-

 And tolerate super high temperatures :)

 Paul Lamar

 Paul,

 Sorry. Mouseititis again. It appears NKH is working on a 10 mm size
 spark plug for the rotary though they wouldn't commit on when it would
 be available for the racing community. They did show me long narrow ten
 mm plugs but they where the bent tang type normally found in piston
 engines. A good guess is they made some concentric iridium tip types
 for Mazda engine research use only. Speaking of which. If you follow
 the course of Mazda engine development you can understand why they are
 playing with dual fuels, specifically the addition of hydrogen. The
 all-hydrogen engine was for testing and probably good PR. Hydrogen or
 better yet, on board generated H00H makes sense if injected in small
 amounts (less than 0.4% by weight) right after gasoline is injected and
 the intake port closes. This would imply the hydrogen fuel is injected
 at the top of the housing. Looking at the 16X housing pictures you can
 see this is so. The H2 burn rate is so rapid that it solves a lot of
 problems associated with trailing plugs and multi sparks. The hydrogen
 or Hydroxl gas fuel first ignites and this in turn ignites the fuel
 droplets.

 My interest in smaller footprint dual plugs was in trying to make the
 dual plug insert a bit narrower to minimize both the liner welded area
 and inner water passage restriction. Closer together also brings both
 sparks into the central rotor depression area instead of near the rotor
 edge. Having the sparks nearby in my thinking would minimize an
 asymmetrical pressure on the rotor face in case one ignition system
 failed.

 Dual fuels adds complexity, as do sequence fired capacitors without a
 doubt, but a loss of the hydrogen injection would not be a show stopper.

 Doug in Japan

 Some of this is discussed in Kenichi Yamamoto's Rotary Engine Bible-1981.
 http://www.wankel.net/~krwright/cars/rx7/manuals.html, page 50-ish

 While people are talking plugs.
 Has anyone experimented with single pronged side fire plugs or RX8 fine
 wire leading plugs VS the older plug styles?

 I have read of folks getting better mileage with side fire plugs:
 http://www.mazspeed.com/sidefire.htm
 http://www.rx7club.com/showthread.php?t=656700

 I have wondered if adding flame front channels from the rotor recess
 towards the apexes might help with the squish areas, possibly with
 trailing negative split.

 Has anyone measured the difference in fuel economy with/without wasted
 spark on the leading plugs?
 Leading to getting rid of the trailing plug entirely, in favor of twin
 leading plugs (at least move the trailing closer to the leading).

 Cheers
 Cary


 yes I have.

 Skip

 Well Skip can you tell us what you found? :)

 Paul Lamar

 Cary,

 Thanks for posting those threads from the RX forum.I plan to go back to
 NGK now and see how many models they have out on their new long skinny
 10mm plugs. I am ready to cut a dual plug insert next weekon the
 test configuration housing so a smaller footprint would make me happy.
 Yes modifyingplugs to side fire may seem to be a hazzle but if they
 last much longer and more importantly are more efficient then that is a
 acceptable trade-off.Question remains on how much energy it would
 takes to fire the smaller plugs. I guessthis means we would also
 have to search for different coils to power them.

 Doug in Japan

Hi Doug;
The 10mm plugs sound like the way to go.
I'll probably try a set of the side fire plugs in the car shortly.  I'll
try to drive
like grandma to pseudo scientifically measure it :)
I expect the side-fire plugs and close plug location will help most with
low
power and leaned out economy modes.  The closer proximity of the plug
and reduced interference of the single electrode should help with
ignitability.
A larger .055"+? gap and stronger spark would probably help as well.

I'm curious, what plug configuration /location have you selected for
testing?

 http://www.wankel.net/~krwright/cars/rx7/manuals.html, page 53
Figure 4.54, always struck me as an interesting chart.  If I interpret
it correctly,
a singleplug results in slower, more complete burning and gets slightly
less HP.
hmmm
Not sure if there is an optimal mechanical advantage factor going on based
on the flame front - need to look at the rotor/eshaft location.
It also me strikes me as a quick fix for passing emissions...
Cheers
Cary


Cary,

On the test engine I have committed to going with leading dual plugs side
by side and leaving the  14mm dia. trailing plug in place with the idea
to see the performance difference between using it or not.  For various
reasons I will not install a 3rd trailing plug.

It would be nice to be able to seal the trailing plug hole without having
to take the engine apart and weld and grind it flat,  but a good way to
do this hasn't occurred to me yet.

Yes I would like to go with 10mm leading plugs.

I found this on-line catalog of Denso plugs and their NGK equivalent.
Perhaps we can find something that will work well..

www.globaldenso.com/en/products/aftermarket/plug/catalog/asia/pdf/
pdfcatalog_asia_all.pdf

Regards

Doug in Japan

Hi Doug,
While you have the engine apart, make a dummy plug that will fit into the
spark plug hole. Make it exactly the same as the business end of the
standard spark plug, but put a "snout" on the electrode end that is
the diameter of the hole in the rotor housing and sufficiently long
to project into the combustion chamber. Touch off the end in the chamber
with a grinder until flush. MARK EACH ONE with position and installation
torque as more or less torque could change it's orientation in the hole
when reinstalled. (Alternately, you could match mark the plug and housing
with adjacent, carefully placed, punch dots). Now you can do your testing
with a spark plug in place the remove it and install the "dummy" plug for
comparison tests.

REMEMBER TO POSITION THE PLUG IN THE HOLE IT WAS MADE TO OCCUPY. Dave M