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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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