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.phpt=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 single plug 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

Ok Guys,
Some of the comments seem to be a little off base. The Smaller plugs should
require the same amount of energy to jump the GAP. The smaller loop-over
sidewire should allow the plug to be a bit closer to the combustion chamber.
That would make the gap a bit more accessible to the mixture, which MAY help
the combustion. The smaller recess should make for a tiny bit higher compression.

The best thing would be for NEW housings to be DESIGNED for the smaller plugs
which would allow the water jacket to be closer to the plug well and it might
help prevent cracking in that area under extreme power use. Mazda versions having
some small trouble cooling that area.I do like the idea of being able to run the
tiny coil-on-plug coils used on the modern motorcycles. Those coils are super light,
and usually are a ferrofluidic type which is great for low hesterisis. These coils
need to work on machines that have a 13,500 RPM redline on the street! They seem a
perfect choice for the multiple spark regimen of the rotary. Take a look at the
newest Honda or Yamaha 600's for good examples.
Bill Jepson

Bill you're exactly right. There is a small group of us that
are intending to mfg. a rotor housing using the small plugs
based on testing results we have accumulated.

Skip

This I got to see :)

Paul Lamar

Dave, Skip,

Thanks for the idea.I noticed that the inside of the trailing plug hole
had a little bevel on it where the factory no doubt took off the burr
after drilling. Wouldn't this small depression still allow some gas
to move from the compression stroke to the exhaust stroke

Bill

Thanks for the lead to the 10mm bike coil on plug info.About the
leading plugs.I was thinking about making a step shaped rectangular
stainless 303 insert with radius ends.It would have dualplug holes
and slip inside a milled out leading plug area of the housing, TIG
welded on the inside, and interface fit on the outside. Another plate
with gasket and plug holes is then bolted both to the outer housing as
well as the insert providing a water tight seal and mechanical strength
between the inner and outer housing. If the stainless insert had
grooves machined onto the outside where contacting coolant so much the
better for heat transfer.CHT sensor could be built into the insert as
well.Existing hole and boss is pretty muchmilled out with this
operation. Water passages should be a few millimeters wider on each side.

It would send you a Rhino file, except the by Windows based lap top just
died.

Doug in Japan

Doug,
I'll look forward to seeing the drawing when you getyou computer running again
Bill Jepson

By the wayDoug, if you were able to weld in an insert you would probably need
to dosome annealing of the welded area. This is a hot area which gets locally
much hotter than the area around the intake port. I am not sure why to run two
plugs inthe leading position anyway,unless it is to ensure lighting a lean
mixture. I believe that running the multiple spark system Paul was talking about
would be more productive. Running a conformal insert with the small plug in it
in BOTH of the conventional locations makes more sense to me. I would like to
see a dyno chart report of improved function with dual plugs in the leading
position before I would do it.All of the information that I have seen in the
past shows that losing the leading plugwas a 80% loss of power, and the loss of
the trailing plug caused a 20% power loss. The key here is thatnon-turbo at
least the trailing plugs are NEEDED and sagnifigant. Filling the area close to
the rotor and getting the plug as close as posible are the only idea that I
think works. Theidea of the "sidefire" modification allows you to put the
conventional plug closer to the combustion chamber safely, that is all it does.
Bill Jepson