I have been using NGK DCPR8E/DCPR8EIX with my JE hi comp pistons. Have not had an issue with piston crown clearance. I have a mate that runs the NGK D8EAs and their iridium version with JE hi comps and skimmed heads (similar squish to no base gasket).
I have not dyno tested a comparison of these plugs.
Something I've just remembered. I have seen a Denso plug closed up by the crown of a Pistal piston in a 98 900 Monster. It was an X24EPR-U9. Probably a great plug, just a smidgen too long for that application. Upon comparison with a DCPR8EIX it did protrude a little more into the combustion chamber.
Any recommendations re plug reach and particular hi comp piston brands? My experience only runs with JEs and Pistals.
Road tested NGK iridium plugs yesterday, back to back on same road course with same fuel, same heat range. Tested up to half throttle "street legal" road test with plug chops
Coils are Kelley coils with Kelly leads and NGK caps. Max advance 2 deg less.
DPR8EA-9 chocolate brown color
DR8EIX light tan/Beige
Leaner looking plugs with the non projected reach plugs. I was a little surprised as I thought the projected reach plugs would give a more complete combustion. At a guess I would say that the particular porting/hi comp piston combination of this particular motor liked where the spark was over the piston crown and where the spark originated in the combustion chamber (with the non PR plugs).
In other words a more complete combustion event. Anyone have any thoughts on this?
From what I recall hearing, the projected nose plugs are better, up to the point where the ground electrode gets too hot.
Makes sense to me.
Have heard/read that if it's too close to the piston that it can be a problem.
A little more info here, and while it's from a long time ago, it's from one of the smartest engine guys (that would actually talk and write about stuff):
http://www.strappe.com/plugs.html (http://www.strappe.com/plugs.html)
I've read that, it's excellent.
I have used PR plugs when I can as they are theoretically better. I'm surprised at the non PR plug running "leaner". It gives the appearance of more complete combustion, or is it just running "hotter"?
Anyone know of any dyno testing regarding this?
Continuing testing.
Noticed that the PR plugs give a slightly faster idle, so thats one for the PR plugs. They do run a darker color which may just be a symptom of their more exposed nature in relation to the inlet charge. That is speculation. The quicker idle is good though and an indication of a more complete combustion event.
So why do the non PR plugs run a leaner looking color? Just because tnere is more complete combustion in a section of the chamber doesn't mean a more complete combustion in the chamber overall and this might offer an explanation. I find this stuff fascinating.
Anyway, the non PR plugs are an option with certain pistons.
Cheers.
They PR plugs may look darker due to being out further into the 'airstream' as you suspect.
As long as they don't overheat the electrodes on a hard run (fast uphill with pillion into the wind on a hot day), there's no loss in running 'em IMO.
Cheers SD
[beer]