NGKBP6ES & BP7ES Plug Test

[William2]

On my rebuilt stock SE engine with Delortto carbs I started using NGK BP7ES plugs. After a long drive I checked the plug colour and found the centre electrode to be correct and the outer metal rim of the plug to be slightly sooty. I then did the same run using BP6ES plugs. This time the centre electrode was similar (grey/brown) but the outer rim was completely clean with no soot. Is it therefore better to stick with these plugs?
The engine idles and picks up with no hesitation so I assume the jetting, etc is fine.

[rgh0]

BP6ES I have found best like you for a normal road twincam engine in normal mixed city / country road driving. BP7ES only really needed in a road car if doing lots of continuous high speed full throttle driving in places like German autobahns or the equivalent

cheers
Rohan

[ecamiel]

what plugs are folks using for hot (160 HP) street motors on the street and for track events? Currently using BP6ES

Eric
64 S1 Hart

[Paul Chapman]

Hello William

I am also now using BP6ES plugs in my tired Twin Cam and it runs a lot better than when I used BP7ES's.

[terryp]

My two old +2s both on Dellortos were definitely happier on BP6ES but the funny thing my current Elan with Strombergs prefers BP7ES, the BP6ES I had originally fitted becoming slightly over burnt.
I think it must be a case of fit and see.

Terry

[HampshireMush]

My S4 SE with Strombergs, which has had some engine mods done by Oselli by a previous owner, came with BP5ES but kept fouling so after reviewing this forum I changed to 6's. Still was getting problems occasionally so had a regular routing of cleaning them. I met another owner at Brooklands one day and he suggested going back to 7's which is what is in the handbook.

I have been using 7's for several months now and they have been by a long way the best - no regular cleaning and engine has run fine hot and cold.



John

[Galwaylotus]

My S4 SE with Strombergs, which has had some engine mods done by Oselli by a previous owner, came with BP5ES but kept fouling so after reviewing this forum I changed to 6's. Still was getting problems occasionally so had a regular routing of cleaning them. I met another owner at Brooklands one day and he suggested going back to 7's which is what is in the handbook.

I have been using 7's for several months now and they have been by a long way the best - no regular cleaning and engine has run fine hot and cold.



John

There must have been something else at work there as BP5ES is a hotter plug than BP6 or BP7. If fouling was caused by too cold a plug then going to 6 or 7 would have made it worse. See NGK's explanation: http://www.ngk.com.au/spark-plugs/technical-information/heat-range-explanation

[RogerFrench]

I wonder if there's some confusion between different makes. NGK heat range numbers run the opposite way from Champion, for example.
Champion N7Y is equivalent to NGK BP7ES (roughly), but a NGK 5 burns hotter, a Champion 5 burns colder.

Also, Stromberg engines run a bit hotter than Weber or Dellorto, explaining Terry's findings.