Calling John Corbani: Spark plug and gap

Pietro,

I run NGK BPR7EIX Iridium plugs gapped to 0.03"-0.04". Have over 5,000 miles on latest set and they look great. Was never able to get much over 2,500 miles on conventional plugs before hard starting became a problem. I changed out a set of NGK Platimun after 15,000 miles and they were still fine, although obsolete. I run standard points with aftermarket replacement for the Dinoplex. Try the NGK Iridium, you will like them.

John

 

If I may make an observation, note that John is running an aftermarket (higher energy) ignition module. You indicated that you are running a stock Dinoplex, as am I. We likely cannot run the .030-.040" plug gap that he is, as our vintage 'plexes are electronically challenged & may not be able to bridge the wider gaps. I set my Iridium sparks at .022, which pushes the factory .016-.020" envelope just a tad. Others in this forum, as well as those folks with V-12s running a duo of Dinoplexes, have succeeded in coaxing a spark of .025" length before having to resort to more modern systems.
Pietro, we should consider the various upgrades/replacements to the Dinoplex that have been discussed in other threads. Modern super-high energy ignition systems firing larger plug gaps can better touch off the fuel/air mix, resulting in: More complete combustion, more power, lower emissions, quicker starting, better economy...as well as freedom from the infamous fouled plugs.
Search the site for previous threads/posts on this subject. John, and several others, have discussed the merits of each available upgrade. The consensus seems to be that any of the upgrades will result in a seat-of-the-pants difference. As I recall, your car is pristine; keepin' it stock appearing is a necessity. You could opt for the stealth unit with modern Bosch components hidden in your Dinoplex case.
Back to your original post, I trust you'll read this before you R&R your plugs. Let me know what you think.
Cheers,
Coop

 

Check your engine plate...tiny gap of .02" is pretty standard on stock coils..

My book (308GTB) indicates range of .015 - .025 MAX.......


More than that is crazy......unless throwing HEI spark of some sort.....

 

I would recommend staying within the factory specs for the gap with your stock ignition system. It is always nice to gap close to the small end to get a good spark. As the plug wears out it goes closer to the larger gap but will stay within specs when it's time to change the plug. If the gap is too large the spark will be weak and you may get oil or fuel fouling of the plug.

 

Pietro and all others,
You all have some points but there are unique factors with the platinimum/iridium plugs. And there are no differences in the output of the ignition system as long as the original coil is left in place. Dinoplex is just first generation transistorized ignition and only problem is the rating of the output transistors. 1968 transistors were pitiful in comparison to modern aftermarket replacements. Even 1975 replacements, not to mention 2007 replacements. When Dinoplex is working, there is just as much spark as the replacements can provide. With the same coil!

The small center electrode of the NGK plugs effectively increases the ability of the HV to jump the gap. There is no problem running a 0.02 gap but there is no advantage and there is less spark area open to the combustion chamber. I find that idle is better with the 0.03-0.04 gap and there is no problem at high RPM. I run up over 7000 now and then and it is sweet.

There is no comparison in lifetimes. The NKG plugs just get dusty, there is no physical wear during spirited highway driving. Track conditions will be different but NGK has plugs for that too.

I have over 20,000 miles on these plugs after trying all others. No comparison with conventional or other brands of plugs with small (but not as small) electrodes. NGK!

John

 

By changing the spark plug the ignition system is now not stock. On this non-stock plug you have found a gap that works well for your car.

My only concern in changing from the factory recommendation is that the heat range of the plug may not be correct. The wrong heat range can damage an engine at sustained high speed.

What is the part number of the spark plug you use?

 

Iridium plugs only come with resistor as far as I can tell. No change whatsoever compared to the Platinum that had no resistor. The resistor guarantees low erosion of the small tip and the radio interference reduction is a free byproduct. Resistor was originally to reduce radio noise in older plugs.

Funny thing happened during last rebuild. Mechanic was adament that my ignition wires should be replaced. He picked a resistor core wire and the car would not fire. Changed plugs, nothing! No matter which kind of plug was in. I told him that he just bought himself a set of wires and had him put the old solid core wires back in. Car fired right up. Car had Delco GM SS-550 plug wires when I bought it 21 years ago. Never had a problem and they are still in there.

John

 

Aren't Iridium's about $50 for six plugs?

I've been running Bosch platinums and they've been great with the MSD, but cost 80% less

 

Have not tried Bosch but did try AC platinum. Trick seems to be size of center electrode. If Bosch is same as NGK, probably work as well. AC is larger and idle suffers. I paid just over $8/plug and figure that is reasonable for 30,000-60,000 miles of no grief. MSD might make a significant difference. I have old Perma Tune box with original Magneto Marelli coil.
John