Spark Plugs

[BobBray]

What is the general consensus on spark plugs these days? For a long time I was running the specified AC C44NS commercial plugs in my 351E. Even though obsolete, they were readily available on Ebay fairly cheap. Truck ran O.K., but it did tend to run on a bit shutting off when good and hot like after a long drive in traffic. I was thinking the plugs might be a little too 'hot' for non-commercial driving. I changed the plugs to the currently recommended platinum AC 41-828, gapped at .040. Runs better! Quiker starts, smoother hot idle and no run-on. I do have a Pertronix ignition with their 3.0 ohm 'Flamethrower' coil, so I am sure the increased gap is not an issue. The old C44NS showed no fouling, oil or excess carbon deposits, insulator tan, end of electrode gray, moderate gap increase.

[Prowbar]

I am running the 478 on propane mostly. Propane burns hotter meaning you need colder plugs. The porcelain on the AC R44XLS plugs in the 305 and 478 was very white. I switched to R43XLS plugs and they are still on the hot side, but a little better.

I am now running NGK BRP6ES plugs (same heat grade as the 43) and I like the NGK plugs better. Can't say I noticed a smoother idle or anything.

I was running the HEI ignition but switched back to points. I find more joy in keeping things original/OEM than aftermarket stuff. No difference in idle or cold starting for me. Still using the stock coil with the resistor wire.

[AZKen]

Commentary, not aimed at anyone:

It really does not matter brand wise. The right threads, the right protrusion into the combustion chamber and gap is all that matters. Plugs are not high tech. They just make a spark. The only moving part is the hype. Condition of motor, rings, timing, rich, lean, manifold heat leaks are what fouls a plug. As some folks have found, going "Hot" is not advantagous and can cause trouble.

Don't fall for sales words like "Hot Spark", "Flamethrower" "performance plugs" "Split Fire"..................We have VERY LOW RPM "Non performance", reliable, high torque, super engineered motors that run on any properly gapped spark. Just make sure you have good plug wires.

[Prowbar]

I agree on that, Ken. A good spark plug won't fix an engine that had bad rings, leaking valves, poor A/F ratio or the like.

[BobBray]

There's a lot of 'gimmicky' spark plugs out there, I agree they don't really work any better than standard plugs. One thing I noticed about the original C44NS plugs is that the center electrode is quite recessed, which usually means hotter plug. The 41-828 electrode protrudes further out. Not sure what the number mean on newer AC plugs, other than '41' means spark plug and the '800' series means 'platinum'.