Randy,

 

What you said is, of course, contrary to my experience and the recommendations made by Light Speed Engineering.

 

Which plugs had "the tips burns down fast or the ceramic crack under the pressures" and what were the pressures?  Were the plugs ever dropped?

 

Are you sure the coils shorted internally because the auto plug gaps were getting larger or were the coils placed in too hot of an environment?    What plugs were used?  It is hard to imagine internal coil arcing in the absence of any plug gap or even the absence of a plug altogether.

 

Which actual auto plugs cracked under full power and/or had the electrodes burned away?  What were the other engine conditions?

 

I have run my 9:1 CR injected 320 at takeoff power (racing is like that) for hours on end with no difficulty - no difficulty with either the EI or the Denso IK27's - where the timing and A/F ratios have been appropriate for the power and the coils are located in an area behind the engine that usually reaches 70C.

 

Anyway, you might find it interesting to read:  http://sparkplugs.com/pdfs/iri.pdf even if you only skip to the conclusions at the end.

 

You might consider getting rid of your massive electrode plugs altogether: http://www.ramaircraft.com/Maintenance-Tips/Spark%20Plugs-Fine-Wire-vs-Massive.htm as it appears that while the fine wire plugs cost three times as much, they also last more than 3 times as long.

 

You may wish to poke around the web for info on the differences betwixt Champion and Unison (Autolite) iridium plugs.

 

BTW,  I noticed that you re-gapped your aviation iridium plugs (out of the box the gaps are too small for EIs, .016-.018.).  This is a very difficult task with Champion plugs (they are happy to re-gap them for you).

 

Finally, I didn't even try the LSE recommended W27EBR (27 heat rating for higher compression engines) since they seemed too cheap.  I did try the W27EMR-C plugs (triple massive electrode), but didn't like them because I could not control all three gaps (well, that was one reason).

 

 

In my 360 I use Iridium plugs with my Jeff Rose EI. They work great. Set to .035.

I wouldn't use car plugs in an aviation engine. They don't work well.

I've seen the tips burns down fast or the ceramic crack under the pressures.

One multiple failure I've seen is on a friends very low time Legacy that has had 3 shorted coils on his LSI system.

This was from the Denso auto plug gaps getting larger from wear then eventually arcing inside the coil.

Another failure in a 360 I've seen from auto plugs is the ceramic cracks under full power and completely burns away the electrodes, damaging the cylinder.

Aviation plugs are made for aviation use and can take the abuse. They last much longer and rarely fail. All the Lancair's in my group stopped using auto plugs.

Uppers are Massives with a mag and lowers are Iridium with an EI.