Why are there so many plug choices? What parameters are most important? For example, my trick flow heads call for auto lite 3924 plugs. But nowhere else do I find them for mopar big block. I saw @AndyF recommend NGK plugs I think 6987. But they are not 440 either. Is it the heads, the block, the ignition, or what else? I have a efi sniper, 512 with hyper spark ignition and I have used the auto lites but wonder if they are correct for the application. Any guidance appreciated.
Spark plugs. Why is it so hard?
- Thread starter Kent mosby
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Kent, they probably recommend those plugs mostly I bet because they are the small 5/8 hex and easier to get to. I'm sure they are "whatever" heat range Trick Flow thinks is best.
448Scamp
Running Free
If you have TF heads they take a 3/4 reach 5/8 hex plug. Most BBM heads took a 5/8 reach 13/16 hex plug. The two are not interchangeable.
Heat range is a different discussion.
Here's a great article on plugs. It even mentions Autolite 3924's.
How to Determine Correct Spark Plug Heat Range
How to Determine Correct Spark Plug Heat Range
Scody21
Just send it
If the reach and threads are the same, then they can interchange to the smaller plug. You don’t want the bigger hex, only difference is the socket size between the two.
I run NGK BKR6E / 6962 in my J heads, Eddy RPM heads and 1.88 heads on my LA’s and my 5.9 magnum Ram.
On the small blocks, Champions first if you can find them, then Autolites, then what ever your head manufacturers recommend.
High Energy Ignition systems are now back down to .045 ths spark plug gaps instead of the .060 ths they used to recommend.
High Energy Ignition systems are now back down to .045 ths spark plug gaps instead of the .060 ths they used to recommend.
Spark plug brand choices is a bit like condoms....you buy your favourite brand.
I have always liked NGKs which was one of the few brands that would last in the early Honda 750 m/c engines. Lucky to make it around the block with Champion R6s...
But I digress, ah memories....
NGK heat range for a Mopar V8 is a '5'. Unless it is at WOT for long periods, has nitrous or other power adder.
I have always liked NGKs which was one of the few brands that would last in the early Honda 750 m/c engines. Lucky to make it around the block with Champion R6s...
But I digress, ah memories....
NGK heat range for a Mopar V8 is a '5'. Unless it is at WOT for long periods, has nitrous or other power adder.
Thanks for the assistance. What are your thoughts on iridium or platinum tip plugs. Any benefits or drawbacks?
448Scamp
Running Free
All that will do is make your wallet thinner. A good copper core plug is all you need.
Bad on me . I thought I was running auto lite. 3924. Nope. I using the ngk zfr6f-11g. also referred to as the 6987 NGK. I probably did this based on what Andy finkbeiner uses and recommends. These plugs have been through a bit. Some of my amateur mistakes were a leaking vacuum at the intake and a bolt on O2 sensor that leaks and caused the motor to run incorrectly. Finally, I ran the drag strip with plug wires 7 and 8 loose or disconnected. and burnt the 6 plug wire on the headers. Man, this feels like going to confession revealing all my failures. BUT, the reason I tell all of this is that I have learned a lot along the journey the past couple years and hopefully, I have corrected everything.
My question now is, Would you run them as is or buy some new ones? I don't know how to read the plugs to know if they are ok.
I did buy some plug insulators, fixed the wires, the 02 sensor was welded and the intake does not leak anymore.
Scody21
Just send it
If your still working on tuning, put some new plugs in. Otherwise, I’d run the set you just shared a pic of..
Those plugs really don't look all that bad. But, for $25 you could get a new set.
I got a new set. I had a $5 O'reilly's card that expires in a week so why not
Only difference is how long they last. Zero performance benefits.
Kent,
Platinum & Iridium plugs do have benefits, but they act like the 'silent partner'. You don't know they are there working in the background.
Bit of housekeeping first. Both std & specialty plugs have copper cores, which are imbedded in a steel case. I remember hysterical claims, by Champion I think it was, when NGK introduced the copper core that the copper would melt, ya da da....
Now, all the plug makers use copper. Plat, Iridium etc are precious metals & cost more. So there must be a benefit if car makers are willing to spend more on plugs.
There are numerous benefits, even for the hot rodder, most important being ignitability. When the spark is established from a cold metal surface, the phenomenon of electrical quench tries to extinguish the spark. The cold metal tries to absorb the heat, put out the spark. That becomes a misfire, not good for power, economy or emissions. By making the electrode smaller, the chances of quench are reduced. A 2.5mm diam centre electrode has 15 times more surface area than a 0.6mm tip. New problem now: thin steel tip will melt. Hence the use of high melting point metals like Plat & Irid for the centre electrode. Another benefit: less arc over voltage is reqd. From NGK, a 0.040" plug gap with std 2.5mm electrode that needs 21,000v to fire only needs 18,000v with an Irid electrode. That means you run a bigger plug gap with the same ign system; obviously the bigger the spark, the more chance of igniting the AF mixture. A gap that grows due to electrode erosion eventually causes a misfire. Erosion is less with P & I electrodes, so they can be left longer before checking the gap, plus they last longer.
Platinum & Iridium plugs do have benefits, but they act like the 'silent partner'. You don't know they are there working in the background.
Bit of housekeeping first. Both std & specialty plugs have copper cores, which are imbedded in a steel case. I remember hysterical claims, by Champion I think it was, when NGK introduced the copper core that the copper would melt, ya da da....
Now, all the plug makers use copper. Plat, Iridium etc are precious metals & cost more. So there must be a benefit if car makers are willing to spend more on plugs.
There are numerous benefits, even for the hot rodder, most important being ignitability. When the spark is established from a cold metal surface, the phenomenon of electrical quench tries to extinguish the spark. The cold metal tries to absorb the heat, put out the spark. That becomes a misfire, not good for power, economy or emissions. By making the electrode smaller, the chances of quench are reduced. A 2.5mm diam centre electrode has 15 times more surface area than a 0.6mm tip. New problem now: thin steel tip will melt. Hence the use of high melting point metals like Plat & Irid for the centre electrode. Another benefit: less arc over voltage is reqd. From NGK, a 0.040" plug gap with std 2.5mm electrode that needs 21,000v to fire only needs 18,000v with an Irid electrode. That means you run a bigger plug gap with the same ign system; obviously the bigger the spark, the more chance of igniting the AF mixture. A gap that grows due to electrode erosion eventually causes a misfire. Erosion is less with P & I electrodes, so they can be left longer before checking the gap, plus they last longer.
Straight from NGK. Note the electrical resistance in ohms of copper compared to all others. Copper is by far the best conductor. The only benefit to iridium and platinum as I said earlier is longevity.
NGK.com: NGK Spark Plug Metal Types
NGK.com: NGK Spark Plug Metal Types
448Scamp
Running Free
OEM’s use non copper plugs for durability as you say. Look at any late model engine and it’s a royal stinker to change plugs in most of them. Plus the average consumer doesn’t change plugs often enough and computer controlled stuff doesn’t deal with worn out plugs very well.
Other than the fine wire center electrode the copper core plugs will outperform all others. And you can get copper core plugs in a fine wire.
I use the NGK as much i can. Had everytime good experience and no fouling except there was something not correct, f.e. during a engine diagnosis on customer cars. I never use a plug that falls to the floor, replace it. Tuned 2 strokes, classic cars, Wankel, nothing bad.
NGK has a good product finder tool. The NGK has a wider heat range than old Bosch plugs, so they forgive more.
Study also the explanations what the numbers and letters tells you about the plugs.
NGK has a good product finder tool. The NGK has a wider heat range than old Bosch plugs, so they forgive more.
Study also the explanations what the numbers and letters tells you about the plugs.
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Pretty sure the Plat/Irid plugs also use copper, but not 100% sure. But it makes no measurable difference to the overall resistance in the spark plug circuit: The 'copper' is in the form of a slug encased inside a steel/nickel core of the centre electrode, about 0.5" long. What do you think the difference is in micro ohms between a piece of steel & copper, both 0.5" long? Then you ADD to the circuit because THESE resistances that are in series & become additive before a spark can be generated: rotor button resistance, rotor air gap, coil sec resistance, spark plug gap, spark plug lead resistance. Millions of ohms. Much ado about nothing.....
What I said about Irid/Plat plugs in post #15 about the extra benefits is 10000% correct.
From the Bosch Automotive handbook 9th edition, 1500 + pages.
" '[ leaning of the mixture ] is accompanied by an increase in the energy demand needed to ignite the mixture. By enlarging the electrode gap, it is possible to increase the volume ignited by the spark & thereby raise the energy content. However, enlarging the electrode gap requires an increase in ign voltage......The electrode gap should be......as large as possible so that the ign spark activates a large volume element & thus results in reliable ign of the A/F mixture by developing a table flame core."
Plat/Irid plugs allow larger gaps with the same ign system, reducing the chances of misfire & increasing the chances of complete combustion.
What I said about Irid/Plat plugs in post #15 about the extra benefits is 10000% correct.
From the Bosch Automotive handbook 9th edition, 1500 + pages.
" '[ leaning of the mixture ] is accompanied by an increase in the energy demand needed to ignite the mixture. By enlarging the electrode gap, it is possible to increase the volume ignited by the spark & thereby raise the energy content. However, enlarging the electrode gap requires an increase in ign voltage......The electrode gap should be......as large as possible so that the ign spark activates a large volume element & thus results in reliable ign of the A/F mixture by developing a table flame core."
Plat/Irid plugs allow larger gaps with the same ign system, reducing the chances of misfire & increasing the chances of complete combustion.
READ the NGK link I posted. The resistance difference is VERY measurable. Copper has them all beat by a good bit. Platinum and Iridium do not allow wider gaps. That's a fallasy. The only thing that "allows" for a wider gap is more voltage. I remember during the late 70s some of the GM HEI plug gaps were .080 and .120 and it was because the GM Hei was really hot and they all used a copper plug. Every one of them.
Thanks for all the good info input guys. Playing around with some mopar HEI Conversions here. Helps to understand things better.
Yes the HEI with the full 12 volt E Core coils do put out the hotter spark. Setting my plug gaps at the .040 ths range, as have heard you don't need the wider gaps as long as there is fuel there to burn. Wider gaps they were using in the lean burn smog area.
Fun to experiment with things.
95 Ford F150 has a nice simple 2 prong + - e core coil that is easy to wire in, runs cool on the full 12 volts, and runs correctly with the HEI setup.
Grabbed some parts from the local You-Pull-It yard to experiment with.
Yes the HEI with the full 12 volt E Core coils do put out the hotter spark. Setting my plug gaps at the .040 ths range, as have heard you don't need the wider gaps as long as there is fuel there to burn. Wider gaps they were using in the lean burn smog area.
Fun to experiment with things.
95 Ford F150 has a nice simple 2 prong + - e core coil that is easy to wire in, runs cool on the full 12 volts, and runs correctly with the HEI setup.
Grabbed some parts from the local You-Pull-It yard to experiment with.
Right! Wider gaps = more resistance and more resistance is hard on ignition coils of all kinds.
448Scamp
Running Free
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