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In a message dated 3/25/2003 8:48:25 AM US Eastern Standard Time,
marv@lancaironline.net writes:
> Perhaps an ice cold racing plug would be a better choice.
> > Lynn E. Hanover
>
> Hi Lynn
> What plugs do you use? Do you have any ideas on what it is in Avgas 100/130
> green that affect my sparky's.
> Ian
I use NGK R6725-115. At $25.00 each, they are probably more than is required
for aircraft use. I run one set all season without a problem. They are
retracted gap fine wire electrode in a very cold heat range. Obviously,
retracted gap would indicate that. I gap them at .010". We run two MSD 6-Ts.
We burn 93 octane regular unleaded car gas, now that we are going fast. The
timing is 27 degrees. We used to burn 87 octane without a problem. I use a
little over one ounce per gallon of RedLine Racing 2 cycle oil.
We also used up all of our piston engine plugs years ago without a problem.
Champion N-80 and N-82, also no problems. The bike shops have suitable plugs
for 2 cycle dirt bikes. I suggest that if you want a fine wire electrode it
has to be retracted or semi retracted. As you have noticed, they can melt
away and cause horrific damage. Getting a piece of fine wire that hot can
cause preignition and break an apex seal.
The gray stuff is lead. Big slow turning piston airplane engines have to use
very slow burning fuel. They cannot stand much ignition advance less the rods
fold up and go away, or a bearing packs up or a wrist pin...........well, you
know the drill. They need peak cylinder pressure well after TDC, so the fuel
burns S..L..O..W... So even low lead has a ton of lead in it. It is not at
all required in a rotary.
The rotary can run on crap. I used to add cheap dino oil to the fuel on top
of the 2 cycle oil, just to kill off some more octane. You can tell it is
smoking too much when it is sitting still, but once under way, you can't tell
the difference. This is with both leading and trailing firing at 20 degrees.
It also reduces engine wear to undetectable. Even when shifting at 9,300 RPM.
Another tip, if you will. When the plug starts to get dirty, you are offering
an additional path across the plug away from the gap. So eventually the plug
shorts out.
I gap very tight at .010". Although others use much larger gaps and dump the
plugs every week. With leaded fuel this may not last as long as it does for
me, but if you get stuck without some spares. You could knock off the big
chunks, and gap it tight and maybe get it going again.
This is also a great way to trouble shoot a secondary ignition problem. If it
is missing at high RPM. Regap the plugs tight and then if it runs fine, the
problem is in the secondary voltage. Like low battery, a wire going away,
dirty plug and so on. If you want to experiment with plugs, be sure to have a
spare junk housing to try them in. Just be sure that the ground electrode
cannot touch the apex seal. And on trailing that the electrode does not
bottom and crack the housing. This is not a big deal unless you try an
extended tip electrode which don't work well anyway.
This is important stuff to think about. The airplane engine is running at or
above a 100% duty cycle. The racing engine is not close to that. In each
lap, the throttle is fully closed on maybe 10% of the time. Once on every up
shift and down shift. And fully closed at high RPMs through long periods of
braking. The rotary can survive a little detonation, but won't take much
preignition.
Lynn E. Hanover
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