Interesting discussion about spark plugs taking place on the Egg site. Seems the Eggs are consuming spark plugs at a rather high rate. Jan is recommending spark plug change at 50 hours (3000 miles, automotive).
Haven't seen pictures, but sounds like very high combustion temps and or pressures to wear a plug at this rate. What do you gearheads know about this?
The EZ30 Subaru has a relatively high specific output (83hp/liter). This would be like a 500hp O-360. OEMs typically fit an NGK 5 heat range to low specific output engines like the naturally aspirated EJ25, 6 heat range to engines like the EZ30 and 7 heat range (higher NGK number is colder) to the Honda S2000 which has a very high specific output of 108-120hp/ liter.
Often when auto engines are used for racing, we select much colder plugs to get reasonable life and reduce the possibilities of pre-ignition. The turbocharged Toyota 2TCs I prepared for road racing were happiest with 8s, having a specific output of over 200hp/ liter as an example.
It seems the low output EJ25s are getting over 850 hours on a set of plugs with little wear but the EZ30s are showing high wear in a fraction of that time. I've recommended trying 7s for these engines and reporting on the life. My own EJ22 turbo was showing high plug wear in 100 hours on $2 7s so I've gone to platinums this time and may try iridiums next.
Engines being flogged like this invariably are often not happy with stock heat range plugs.
Eggenfellner on Spark Plugs
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