Worn spark plugs power loss if there's no misfire?

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Truckedup
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Worn spark plugs power loss if there's no misfire?

Post by Truckedup »

Let's say you have a later model non high performance vehicle...You replace the spark plugs that are very worn with huge gaps..The engine appeared to run fine with the old plugs, no noticeable misfire , smooth, good acceleration.... Do you think the new plugs would improve power and or give better fuel mileage? Is a spark plug one of those things that function properly no matter how worn unless there is misfiring? Thanks
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roc
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Re: Worn spark plugs power loss if there's no misfire?

Post by roc »

Hey Truckedup, in my experience, a bad plug starts causing problem on conditions that's harder to ignite (e.g. high cylinder pressure). On a N/A engine, that's usually the bug after a throttle tip-in (when the combustion chamber is temporarily filled with nearly atmospheric pressure). On turbos, with boost goes up. I worked with Natural Gas vehicles in early 90's, man, NG is extremely tricky to ignite, and educated some about ignitions. I don't have experience with them hurting steady-state power before they reach that point.

PS.: Big fan of your race bikes.
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Re: Worn spark plugs power loss if there's no misfire?

Post by Truckedup »

Roc, I put new plugs in my wife's 09 Ford Ranger 4.0 5 speed, the engine seems to respond better when accelerating moderately through the gears.The old plugs were standard Autolite worn to nearly .080 gap (.054 new), the center electrode was rounded..New plugs are NGK platinum ...

Thanks for noticing my bikes...The double engine Triumph had some minor issues last year that prevented it's full potential.There are no guidelines for building this stuff, trial and error grass roots engineering. I'm working on it now ...I'm sure the Harley dominated 1350cc push rod class will take notice :D There also rumors of a super secret destroked big bore Harley Sportster for the 1000 cc class...
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Re: Worn spark plugs power loss if there's no misfire?

Post by In-Tech »

Hi Truckedup,
A few months ago I was tuning a newer stock vette with ~24k miles, stock AC-Delco platinum plugs and without PCM logged misfires I was seeing some weird things in my own datalogs. I screwed in a new set of NGK TR6 v-power copper and without having touched the tune yet, it picked up 20 RWHP. Outstanding...was it the new plugs, was it because it was 1 heat range cooler, or both? I tuned another 30 RWHP out of it and, needless to say, the customer was extremely pleased.
Again, no driveability issues to start with. Of course I would think age adds resistance to the plug, does that equate to retarded timing?
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: Worn spark plugs power loss if there's no misfire?

Post by Walter R. Malik »

Truckedup wrote: Mon Feb 19, 2018 6:49 pm Let's say you have a later model non high performance vehicle...You replace the spark plugs that are very worn with huge gaps..The engine appeared to run fine with the old plugs, no noticeable misfire , smooth, good acceleration.... Do you think the new plugs would improve power and or give better fuel mileage? Is a spark plug one of those things that function properly no matter how worn unless there is misfiring? Thanks
Not necessarily always a power increase but, that sure can happen; a large amount of power increase, too.
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Re: Worn spark plugs power loss if there's no misfire?

Post by roc »

Well... .080" isn't a gap, it's a distance! :shock: Joke aside, this is where the Natural Gas would school me... these plugs could run alright on gasoline, but it wouldn't drive around the block on NG (and customers would naturally complaint about the NG fuel system, until I'd loan them a good ignition system). Do you remember how the NGK iridium were gapped?

It's possible that those old plugs could still perform alright if your wife's Ford Ranger was automatic, which doesn't lug the engine as much as the manual box can. Lugging means higher charge pressure (harder to ignite).

As for the bikes, I wished I lived closer, I'd love to watch them in person. I admire you going against the grain, good for you. There's Burt Munro's The World's Fastest Indian, and there's Truckedup, the Fastest Triumph's!
Last edited by roc on Mon Feb 19, 2018 8:30 pm, edited 1 time in total.
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Re: Worn spark plugs power loss if there's no misfire?

Post by roc »

In-Tech wrote: Mon Feb 19, 2018 8:10 pm Hi Truckedup,
A few months ago I was tuning a newer stock vette with ~24k miles, stock AC-Delco platinum plugs and without PCM logged misfires I was seeing some weird things in my own datalogs. I screwed in a new set of NGK TR6 v-power copper and without having touched the tune yet, it picked up 20 RWHP. Outstanding...was it the new plugs, was it because it was 1 heat range cooler, or both? I tuned another 30 RWHP out of it and, needless to say, the customer was extremely pleased.
Again, no driveability issues to start with. Of course I would think age adds resistance to the plug, does that equate to retarded timing?
In-Tech, I'm not saying that's the case, but it could be. I think some modern ignition systems can react differently to different plugs and cause havoc until the right plug is installed. Hopefully someone more experienced (Tuner?) can confirm this theory.
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Re: Worn spark plugs power loss if there's no misfire?

Post by David Redszus »

Spark plugs with rounded electrode edges and excessive air gaps require greater voltage in order to fire.
The increased required voltage will result in a diminished spark duration. If the engine is sensitive to reduced spark duration then a reduction in performance can result. If a V-8 engine had 10% misfires, how would you know?
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Re: Worn spark plugs power loss if there's no misfire?

Post by bobalattie »

A perfect example of this is the 3 valve 5.4l ford engine from 2004-early build 2008.. fresh plugs make a huge difference in these engines.. I recommend new spark plugs at 50k all the time..
I’ve made believers out of a lot of people with this service interval.. very few actually make it to the 100k service interval that ford recommends...
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Re: Worn spark plugs power loss if there's no misfire?

Post by user-23911 »

A bigger gap will spark later.
A smaller gap will spark sooner.


But a smaller gap will also give a slower overall burn and a bigger gap will give a quicker burn.
So somewhere in the middle there's an optimum.


It's not going to make a lot of difference but it might be the same as adjusting the timing advance.
If you regap the old plugs there will be zero difference from new ones.
Unless you sell them for a living in which case you should always use new ones.
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Re: Worn spark plugs power loss if there's no misfire?

Post by jsgarage »

Off-topic, Truckedup, but don't worry too much about the Harleys; I'm old enough to remember when the Hogslayer used to come out and play....
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Re: Worn spark plugs power loss if there's no misfire?

Post by Circlotron »

Those skinny coils that fit down the hole to the plug are by necessity quite small and sometimes are relatively low energy. 25 milliJoules is not an unusual figure. As the plug starts to wear, the energy margin above what is necessary would get used up pretty quick in some cases. That might account for why some engines respond so noticeably to new plugs at relatively low mileage.
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Re: Worn spark plugs power loss if there's no misfire?

Post by Truckedup »

David Redszus wrote: Mon Feb 19, 2018 9:33 pm Spark plugs with rounded electrode edges and excessive air gaps require greater voltage in order to fire.
The increased required voltage will result in a diminished spark duration. If the engine is sensitive to reduced spark duration then a reduction in performance can result. If a V-8 engine had 10% misfires, how would you know?
Yes, it can be difficult to detect slight misfiring in certain situations ...I don't know at what point this can trigger a check engine light in a late model vehicle..
I've mentioned here before my 03 4.8 Silverado 5 speed that will flash the CEL if the engine is held at a steady 2500-3000 rpm with light load (second -fourth gear..I can feel the slight surging or lean misfire....To me, the stick Chevy has a more pronounced engine and transmission feel that the "numb" SOHC V6 and 5 speed in the Ranger...
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Re: Worn spark plugs power loss if there's no misfire?

Post by pdq67 »

My Buddy Doc took his old Jeep Cherokee in for an oil/filter change and they looked in their service records on it and said, "We've never did a full tune-up to it, how many miles does it have on it?"..

He looked and said, 175,000! Sucker had never been touched!

Well, they pulled the plugs and replaced them and there was no tips on the old plugs!

Doc said that it runs a lot better now, but was OK before the tune-up. Go figure??

I laughed!

Same deal with his old '70 slant-6 Duster. 175,000 miles on it and its valve cover had never been off! It ran fine sewing machining right along at idle.. And I laughed!

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Re: Worn spark plugs power loss if there's no misfire?

Post by Truckedup »

pdq67 wrote: Tue Feb 20, 2018 7:53 am My Buddy Doc took his old Jeep Cherokee in for an oil/filter change and they looked in their service records on it and said, "We've never did a full tune-up to it, how many miles does it have on it?"..

He looked and said, 175,000! Sucker had never been touched!

Well, they pulled the plugs and replaced them and there was no tips on the old plugs!

Doc said that it runs a lot better now, but was OK before the tune-up. Go figure??

I laughed!

Same deal with his old '70 slant-6 Duster. 175,000 miles on it and its valve cover had never been off! It ran fine sewing machining right along at idle.. And I laughed!

pdq67
I have owned five bought used Cherokee 4.0 's over the last 20 years... The engines are "easy" on spark plugs and standard copper plugs will show little wear in 25,000 miles..And replacing them usually shows no difference in performance...But 175k ? I have my doubts because the cap ,rotor and coil ignition used before 2000 would have likely be burnt into uselessness from the excessive voltage needed to fire the plugs..
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