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Old 05-23-2020, 07:44 AM
rvdave rvdave is offline
Join Date: Jun 2005
Posts: 426
Default Spark plugs and heat range

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?
Dave Ford
Cadillac, Mi
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Old 05-23-2020, 07:54 AM
lr172 lr172 is online now
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,870

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.

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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Old 05-23-2020, 08:00 AM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,604

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.

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 439.3 hrs. on the Hobbs,
RV10 95% built- Sold 2016

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