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Spark plugs and heat range

rvdave

Well Known Member
Is there a relationship between heat range of plugs and running lop and what would be the science behind that either way? I mean lop operation usually means throttling back(?) which reduces map which changes timing on most ei systems, does a colder or hotter plug make any difference to get to lower fuel burns lop?
 
heat range has nothing to do with cylinder performance or ability to ignite the fuel charge and certainly not related to timing. You want a heat range that leaves the plug hot enough to burn off deposits, but cool enough to not create pre-ignition.

Larry
 
Plug heat range for a given engine design is usually selected on the basis of sustained hp output levels. Ideally this keeps the firing tip warm enough not to foul during idle operation and cool enough to live and not cause pre-ignition at full power.

Where a stock Lycoming often uses an 8 heat range NGK, some operators use 9s (1 heat range colder) with no issue and we'd normally use a 10 or colder plug in a race engine which is seeing a lot more heat than a stock application.

LOP operation generally splits idle and full power ranges so nothing special is required here. CHTs and EGTs are not at maximum during LOP.
 
I need the brain trust on this one. I have an IO-320 B1A in my -9A with dual LSE plasma III ignition and 9:1 compression pistons. I am not the builder. The original builder ran NGK BR8ES plugs but Klaus "told" me to run the Denso IK27. As far as I can tell, the Denso is slightly cooler plug than the NGK 8 heat range. I'm just going by the charts I can find on Professor Google. Before my trip to the Caribbean in March, I put in all new NGK BR8ES plugs. They now have approximately 100 hours on them. I fly LOP, as a practice. Took the plugs out today as I'm going to do a compression check and they're all black, making me think the plug is too cool a heat rating. My confusion is that my pistons are 9:1, not 8.5:1 so, if anything, they really should want a cooler not hotter rating, right? Can someone give me some knowledge and guidance here?

Thanks in advance for everyone's thoughts,
David
 
Denso 27s are about the same as NGK 9s. IMO IKH24s or NGK 8s should work fine for you. A half point of CR isn't significant here.
 
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