Double platinum spark plugs made me lose power. WHY? - Page 2 - JeepForum.com
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post #16 of 48 Old 08-29-2021, 06:07 AM Thread Starter
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Originally Posted by leadsled jeep View Post
I used to design spark plugs for turbine engines back at Unison in FL twenty years ago. I am a materials engineer (MS) though specializing in ceramics.

Pt electrodes should be used when erosion is the main concern. Sparks liberate a tiny bit of metal with each event. Pt resists erosion better than standard plugs. Thatís why plugs round off over time. Spark ya like to jump from sharp corners & these erode over time. Iridium does much the same thing. If you have trouble getting to / reaching plugs to change then yes by all means use them. If access isnít a problem thereís only the downside of slightly greater resistance and slightly less energy with each spark event.

Double ground electrodes is a marketing ploy also really. It does allow the center electrode to use more of its sharp edges BUT it also shields the gas from the spark also. Gimmic really.
Thanks for the explanation.
I had no idea about the resistance of the copper Vs. platinum and the spark each one produces.
It makes a little more sense now why those plugs made me lose power, if the spark is weaker.

I have 4 Jeeps. 3 with the 4.0, and one with a old AMC V8 (401). They all have copper plugs in them, and now they will never have anything but copper plugs.


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post #17 of 48 Old 08-29-2021, 06:27 AM
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So bad spark plugs can bog down an engine without misfiring? I always thought if a plug was bad it would misfire. I am having a hard time buying the theory that weak spark plugs can make an engine have less power without misfiring. I will have a chance to prove it to myself. I have a WJ that seems to have less power than my other one. It does have platinum plugs and runs nice and smooth though. If I put some champion copper plugs in it I should notice a nice power increase right? I'll try to make time for that experiment in the next month or two and I'll report back whether it was a waste of time and money or not.


Platinum plugs made my 76 Camaro a completely different car . I have never looked back to the old AC plug days.
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post #18 of 48 Old 08-31-2021, 04:26 PM
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They can. I won't (can't, lol ) get into why, I believe it has to do with the energy of the ignition. I race an old Harley in vintage drags, it is VERY finicky about the plugs. And believe me, old drag racers riding old crap will try any trick in the book for a .01 of a second. The fancier and more modern the plug the crappier it runs, and it is running dual plugs. And I think that is the key, I have 2 plugs firing off the a dual outlet coil but it is still only one coil, and it is not a wasted spark ignition. It runs noticeably better on lawnmower style Champions (R5's, can't get much more basic than that) with the electrode cut back to terminate exactly halfway across the diameter of the center electrode and indexed with the gap toward the intake valve.

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post #19 of 48 Old 09-07-2021, 09:10 AM
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Saying an engine would “bog down” with platinum plugs when it was designed for standard plugs would be a gross exaggeration. Think of it as “best spark event possible” and “best flame front” as sufficient energy is discharged.

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post #20 of 48 Old 09-07-2021, 02:49 PM
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Quote:
Originally Posted by leadsled jeep View Post
I used to design spark plugs for turbine engines back at Unison in FL twenty years ago. I am a materials engineer (MS) though specializing in ceramics.

Pt electrodes should be used when erosion is the main concern. Sparks liberate a tiny bit of metal with each event. Pt resists erosion better than standard plugs. Thatís why plugs round off over time. Spark ya like to jump from sharp corners & these erode over time. Iridium does much the same thing. If you have trouble getting to / reaching plugs to change then yes by all means use them. If access isnít a problem thereís only the downside of slightly greater resistance and slightly less energy with each spark event.

Double ground electrodes is a marketing ploy also really. It does allow the center electrode to use more of its sharp edges BUT it also shields the gas from the spark also. Gimmic really.
There is also a bit of electrical engineering and physics in the overall system equation. From a power/energy standpoint, the rule is that maximum power transfer is obtained when the load impedance equals the source impedance. One can substitute resistance for the word impedance to make things simple, but since we are talking about a pulse of energy, it is really an AC circuit and not DC. If platinum sparkplugs (e.g. the load) have a different impedance than the copper (which they do) then the energy created by the field collapsing in the ignition coil is not totally transferred to the sparkplug. Generally speaking, it take ~20K volts to make a sparkplug spark. The interesting thing is that the high voltage potential is required to begin ionization of the gas, and the voltage goes to near zero after ionization and the current flow sustains the ionizaiton. If there is less current (directly affected by the plug resistance) the spark will become weakened, thus directly affecting the ignition of the fuel.
Been many years since I studied this phenomena so I can't quote numbers, just the physics behind it. I am sure there are studies out there identified how much a resistance change in spark plugs affects energy transfer. We see it as 'a badly performing engine'
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post #21 of 48 Old 09-08-2021, 10:46 AM
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Quote:
Originally Posted by leadsled jeep View Post
Double ground electrodes is a marketing ploy also really. It does allow the center electrode to use more of its sharp edges BUT it also shields the gas from the spark also. Gimmic really.
Interesting....
I had an old Alfa Romeo Alfetta, they used Golden Lodge 2HL spark plugs, they had 4 ground electrodes
All old Alfa Romeo in that age used that spark plugs.
But the engine behaviour was deeply different if using single ground spark plugs...


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post #22 of 48 Old 09-09-2021, 05:35 AM
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Yes. Some designs are quite BAD about masking the spark exposure with extra ground electrodes. I’ve seen some that were horrible. Those look quite good actually as they are all four off to the side only.
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post #23 of 48 Old 09-09-2021, 05:38 AM
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Look at my profile pic and see the single L ground electrode. That blocks the spark to some degree as the spark won’t see the fuel behind the electrode. Now imagine another like it. I’ve seen worse even.
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post #24 of 48 Old 09-10-2021, 10:22 AM
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I remember back in mid-90’s I had a 95’ Dodge Avenger and changed Spark Plugs out to a performance brand called Split-Fire (4x Prong)...Can’t remember if it did any better then stock, but probably Snake-ish Oil.
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post #25 of 48 Old 09-10-2021, 03:12 PM
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[QUOTE=leadsled jeep;41352285]Look at my profile pic and see the single L ground electrode. That blocks the spark to some degree as the spark wonít see the fuel behind the electrode. Now imagine another like it. Iíve seen worse even.[/QUOTE


Yep, and why many index them to point the open end toward the intake valve. On my super tall dome piston Harley I have 2 plugs per cylinder and they both point open end toward the intake/top of piston area.
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post #26 of 48 Old 09-10-2021, 09:21 PM
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Quote:
Originally Posted by mak_v8 View Post
Interesting....
I had an old Alfa Romeo Alfetta, they used Golden Lodge 2HL spark plugs, they had 4 ground electrodes
All old Alfa Romeo in that age used that spark plugs.
But the engine behaviour was deeply different if using single ground spark plugs...




Those must have been fun to "gap".

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post #27 of 48 Old 09-10-2021, 10:58 PM
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All this debate can be settled by me. Anyone who is into cars should know to only use the plugs specified by the manufacturer. The engineers spent lots of time choosing the right plug that works with the engine and ignition system. Don’t let the dimwit at autozone talk you into more expensive plugs that he claims are better but in reality worse. Ive heard at Chrysler training that the wrong plugs on a hemi put out a different radio frequency causing issues with the tire pressure monitor and other electrical systems. Imagine trying to diagnose that
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post #28 of 48 Old 09-11-2021, 07:22 AM
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Originally Posted by rjh41388 View Post
All this debate can be settled by me. Anyone who is into cars should know to only use the plugs specified by the manufacturer. The engineers spent lots of time choosing the right plug that works with the engine and ignition system. Don’t let the dimwit at autozone talk you into more expensive plugs that he claims are better but in reality worse. Ive heard at Chrysler training that the wrong plugs on a hemi put out a different radio frequency causing issues with the tire pressure monitor and other electrical systems. Imagine trying to diagnose that

So those 50 year old AC plugs are still the best plug to use in a 50 year old car? No progress has been made in the last 50 years? All my old GM V8's love platinum plugs and I don't have to replace them every year. I could never get 2 years out of the old AC's.


I still can't wait for that nice power increase when I put those copper plugs in my WJ. Hopefully this month.
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post #29 of 48 Old 09-11-2021, 11:15 AM
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Originally Posted by WJ60 View Post
Those must have been fun to "gap".
@WJ60 ,
LOL
In theory that plugs were supposed to last 4 times the single ground ones, and their four gaps were not adjustable.

Today these plugs are no more produced and there is a market born around new and used plugs...; you can see crazy prices around the web.
Alfa Romeo entusiasts have always problems...
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post #30 of 48 Old 10-14-2021, 04:48 PM
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Thanks for the fix. Had the same problem, pulse a slight miss due to too much anti-seize on a few plugs. Cleaned up the holes and put stock plugs in. Runs great now.
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