The Official 356Talk Forum

NGK. BP6HS in any engine that has the clearance. B6HS on the others that do not. Sometimes a 7 heat range depending on the engine build.

I'm using 4111 NGKs in all my 356s. Good results in many cars, over many years. ………………..Jim.

NGK has 2 numbering systems for each part. 4111 is a BP5HS which is on the hot side. I would use a 6 on most street cars, 7 on modified engines or for very aggressive driving. The 5 is for gentlemen with very reserved and socially responsible driving characteristics, like Jim.

But we like Jim anyway.

I need a BP4HS for my sedate driving style.

Eric Wills wrote:NGK. BP6HS in any engine that has the clearance. B6HS on the others that do not. Sometimes a 7 heat range depending on the engine build.

Years ago, the "P" plugs seemed to avoid fouling better than the non-"P" plugs under the claim that the projected tip got 'dusted off' by the turbulence in the chamber. But that was long enough ago when we still got lead in the gas and I didn't bother overmuch with the quench clearance, so they worked.
While it could also be better QC on the plugs, a fouled plug has been pretty rare over the last, say 20 years in my experience. Tightening up the quench and using the non-"P" plugs hasn't delivered a fouled plug in a LONG time.

Eric Wills wrote:NGK. BP6HS in any engine that has the clearance. B6HS on the others that do not. Sometimes a 7 heat range depending on the engine build.

Ditto. Have used NGK BP6HS in both of my C coupes for over 15 years.

Chuck Young, my partner in crime builds all the motors here. About 30 per year. I use Carrillo rods, and Shasta Pistons and cyls. We balance and measure everything. He always says, why do you bother Jim, your cars only see 3500 RPM.

Cliff is right. ..Jim.

Cliff, is the vent in question facing the right direction. On my sons AC, I had it 180 degrees wrong, and it spit oil until I turned it around. ……………….Jim.

Hi Jim, I think you are right about the vent.

Like Eric said, be careful with projected nose plugs. Those marks on the piston crown are from the ground tang of projected nose plugs.

My engine had Denso W20PP's in it for 21,000 miles(oops, forgot to replace them earlier) and had no issues even after three long trips. Just installed NGK's. Will replace on regular basis in future.

Leo Dreisilker wrote:My engine had Denso W20PP's in it for 21,000 miles(oops, forgot to replace them earlier) and had no issues even after three long trips. Just installed NGK's. Will replace on regular basis in future.

My comment earlier suggests there is no reason for "P" (projected tip) plugs since lead was removed from gasoline; I'd say most any plug is pretty 'durable' now. I don't know if this is the direct result of the lead or some combustion by-products, but fouled plugs have become pretty rare.
Not sure what a "regular basis" is but you might wait until you find some issue. And if you are getting 21K miles from you current choice, well, I might change to those.
Aside:
Several years back (maybe more), I got the minutes from a Benz tech session where some questioned the recommendation of changing the plugs at 75,000 miles (that's from memory, but it was a really big number. I really think, from memory, it was 100K miles)
The only gripe concerned the build-up of deposits on the exposed threads, making removal difficult. No one suggested the plugs wouldn't do the job. And I'd also bet if you stuck with the recommended plugs, there would be no 'exposed threads' in your Benz.

It's not the same, but it seems like modern cars are typically still running perfectly on original plugs at 140 K miles. If it ran well, I wouldn't feel bad at still having my 356 plugs in at 21 K miles.

Around 15 years ago I bought a new Ford F250 with a V8. That engine had a very odd spark plug whose end looked like the St. Louis Arch. It was projected to put the spark kernel well into the chamber and I guess the arch allowed the spark to jump to the easiest to attain point. The plugs were not meant to be changed much but when you did you often had an expensive problem because they froze in place and long breaker bars and WD-40 had to be used. Unfortunately that doesn't always end well and the plug snaps in two. Then you had to make an attempt with a fancy Easy-Out and that didn't always work. Final step, remove the cylinder heads. Owners of these engines don't change plugs and pray for no plug failures.

Ron, although extended tip plugs do run cleaner they also have the benefit of placing the spark kernel deeper into the chamber and that results in a better flame front and more complete combustion in cases where there is room for them. On the other hand, if you remove "normal" tip plugs from an engine DO NOT install extended tip plugs unless you are 100% certain that there is room for them. A strong hit to a plug can break off ceramic chunks that are extremely hard and will score the hell out of your cylinders.