Let's talk spark plugs

i use the NGKBP6ES plugs as my "standard" carb 308 plug. i have no emissions stuff to worry about and run 55 idle and 135 main jets.

i have used the BP5ES plugs, but they only seem to work well on cars that are runing rich and not in a proper state of tune due to wear, carb float heights or carb sync bieng off.

this is just what i have seen and learned from my 4 carb 308s. i am not saying the 5 heat range is unsafe. i tested this theory on one of my old 308s by running the BP6ES plugs. plugs were near text book perfect when removed and read. i then installed a set of 8 BP5ES plugs. water temps were higher under load, and oil temps started to rise. not enough to cause a mechanical failure, but enough to notice under load from the " normal " 6 heat range.

i think the carb cars had a heat range of 7 for the OEM / emissions equipped cars.

 

A "hotter" plug is a bit longer and sticks into the fire a bit more, a colder plug a bit shorter and doesn't. You want it hot enough not to soot-up and cold enough not to blister. The general rule is you want to run the coldest plug you can with a soot problem. In therory a colder plug will let you run a bit lower octane if you are right on the edge. I've never heard of any of the things reaper says he had.

 

Expanding on what mk e says, the plug heat range is an indication on how well the ceramic insulator can use the metal jacket as a heat sink. The different amounts of allowed heat dissappation (sp?) are so the plug stays right in the sweet spot - hot enough for no oil fouling, no soot, cool enough that it doesn't self-destruct or become hot enough to start the fire without a spark. Probably you can can go a number either way from the right selection and still be fine, (especially since you pull your plugs every 500 miles to look at them! )

Running a cooler plug alone should not affect the engine oil/water temperature unless you have something else going on (detonation or fouling, for example).

 

I ran NGK BP6ESs in my '84 Mondial and they performed beautifully. Plenty of power, ran clean, no detonation, never a problem.

 

I run 5's and never had a problem. They burn very clean and I don't have any temp issues. My WT runs at 170* as does my oil temp. Car pulls great and I have no problems at slow speeds in 5th gear. I ran 6's once and after a while they would load up a foul. With cold starting without a choke they tended to foul and never come back until you pulled them and dried them up. No problem with the 5's. Also run the timing at 7* BTDC at 1000rpm. REsister wires and black extenders. So if you are running good with the 5's I'd stop worrying about tinkering and get out there and DRIVE. Had a super day today in NY and had fun out on the country roads. Enjoy the ride

 

Should I use the same thing for my 84 308 QV?

 

Not sure if this helps but i put one step hotter plugs in my '86 mondial3.2 and i noticed that it idles a little higher and now pops and backfires on occaison when i shut it down. Sorry, but not able to see what brand and number i used.