I have been testing plugs along with long reach adapters. I started with an RPM drop of 120 with the standard NGK plugs... switching to Iridium Denso brought that down to 60 or so... the same Denso plugs in long reach form have the drop down to 40. All of the plugs seemed to work well with the exception of a single NGK installed in the bottom of #4 that accumulated quite a bit of debris.
The long reach adapters that I found are from
http://www.sparkplugadapters.com/services.html (they focus on farm tractor performance). The adaptors were cheap (6 each including shipping). They are machined anticipating a taper seat but will accommodate a gasket seat which is how it works out to be longer...
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| long reach auto plug compared with the long reach massive aviation plug |
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| these adapters are not ideal since they are cut to accommodate a tapered seal or a gasket seal... I added some high temp RTV on the threads to fill the void from the tapper cut |
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| after several hours plug color is looking very nice |
