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I Searched All Forums And Couldn't Find An Old Thread On This. What Should I Gap My Plugs At? I Got A S.b.c. 383, Accel Hei, Accel Plugs, 8.8 Mm Wires. Thanks...

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I've always ran between .035" to .045" depending on the compression, power adder, etc... Higher compression, nitrous, boost, etc. requires a tighter gap.
 

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The same.

Large plug caps are for lower compression lean burn engines. And if used in a normal or high compression engine it will enhance detonation.

This may sound confusing.

The wider the gap:
The longer the spark travels, the longer it travels is also longer in time.

The Shorter the gap:
The spark travels very short and is very fast
Less time!


If the plug has too much time, it will ignite all the fuel before the compression cycle is completed, causing detonation.

When the spark plug fires it starts the power cycle, usually before the compression cycle has completed, so that compression can also help with the complete burn. if the burn is completed to much you have detonation.

Same as to much timing advance.

I hope I wrote this were you can understand.

Instruction and illustration has never been my cup of tee. Hands on verbal instruction is my main suit.

Al
 

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The same.

Large plug caps are for lower compression lean burn engines. And if used in a normal or high compression engine it will enhance detonation.

This may sound confusing.

The wider the gap:
The longer the spark travels, the longer it travels is also longer in time.

The Shorter the gap:
The spark travels very short and is very fast
Less time!


If the plug has too much time, it will ignite all the fuel before the compression cycle is completed, causing detonation.

When the spark plug fires it starts the power cycle, usually before the compression cycle has completed, so that compression can also help with the complete burn. if the burn is completed to much you have detonation.

Same as to much timing advance.

I hope I wrote this were you can understand.

Instruction and illustration has never been my cup of tee. Hands on verbal instruction is my main suit.

Al
Made good sense!! Same reason we used to sometimes widen or tighten gaps on certain lean cylinders on the dyno. Nowadays with programable ignition systems (MSD 7531, etc..) you don't hear so much about it anymore. With the boxes we can pull timing from each individual cylinder to balance out the egt's..
 

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Hi


Do you guys have pretty good luck with Accel spark plugs?


I have had so many problems I have not used them in years.


Just wondering


Thanks

Jeff
 

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Just to be a devil's advocate... Al

wider gaps and closer gaps are not really all that different when you consider the speed of light. 186,000 miles per second.. what you talking about in speed difference between .032 and .045 gap is less than nano a second or two....

the difference from where I see it is the gap..... the current has to bridge and how much ionization needs to happen to make the spark jump... the greater the distance the hotter the strike... the arc is hotter the greater the gap.... thats you detonation..... hotter spark... with the same heat range plug
 

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Just to be a devil's advocate... Al

wider gaps and closer gaps are not really all that different when you consider the speed of light. 186,000 miles per second.. what you talking about in speed difference between .032 and .045 gap is less than nano a second or two....

the difference from where I see it is the gap..... the current has to bridge and how much ionization needs to happen to make the spark jump... the greater the distance the hotter the strike... the arc is hotter the greater the gap.... thats you detonation..... hotter spark... with the same heat range plug

The way I understand it is the tighter plug gaps give a more intense spark for a shorter duration while the larger gaps produce a weaker spark over a longer duration but has a tendency to be too weak for higher cylinder pressures and more commonly will lead to a miss-fire or cross-fire in the distributor cap (because it's the easier path) and will fire the next cylinder WAY too soon because it's the next closest terminal (especially if the phasing is a smidge off, since EVERYBODY checks that.:rolleyes:.).. The real difference comes with flame propagation. The larger gaps can start a larger flame front and thus cause a faster burn (and possibly detonation). Besides, @ 4000+ rpm, everything happens in micro & nano seconds.:D

When it comes down to true performance applications, it's not the gap that causes detonation, but the longer thinner ground strap that's found on most stock replacement plugs. It has a tendency to turn into a glow plug because it can't dissipate heat fast enough. That's why most of your performance plugs have a short, thick ground strap and the all out racing series plugs have ground straps made of inconel..:eek: The reason a lot of racers are staying away from them is because they would rather melt the strap and put the fire out than melt or break a piston..

As for the Accell plugs....I rank them in the same category as the splitfires....Junk. The standard NGK plugs tend to be a bit shorter than the A/C Delco or Autolight counterparts (for tight fit applications) and I've had great luck with them..
 

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Hi Veno.


Do you think the spark jumps at the speed of light?


I agree that typically a wider gap requires a higher level of coil saturation and thus a higher voltage spark.


In my opinion the issue can get kinda complicated by a lot of factors. I have seen where just changing a camshaft design will alter flame travel enough to require a different plug gap.


Like D-Man was saying, I have certain applications that i will use different gaps in different cyls, and to complicate things even more I have seen several instances of what worked the best on a dyno not give the best results on the track.



I guess in my uniformed view I see the spark plug and/or gap greatly influencing the "effective" timing of air/fuel ignition.


One of the major drawbacks to larger than needed gaps on a high compression, high rpm engine (again in my opinion) is that it is much harder to jump the gap the higher the cyl pressure is, and this can cause a high speed misfire or worse.


To me the cyl temp and plug heat range kinda go hand in hand.


Like I said, in my opinion its kind of complicated and Im sure I have complicated it even worse.



Jeff
 

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Just to be a devil's advocate... Al

wider gaps and closer gaps are not really all that different when you consider the speed of light. 186,000 miles per second.. what you talking about in speed difference between .032 and .045 gap is less than nano a second or two....
i would think this would not be the case!
we are more concerned with the speed of the heat wave,not light. heat has a much slower speed than light.

heat is a mechanical waveform.(will not travel through a vacuum) light is a radiant waveform(will travel through a vacuum).

heat waveform is effected by density(compression) so the spark gap has a significant effect.

on a sidenote:

light is a very special waveform!! it is actually BOTH radiant and mechanical....

it will travel through a vacuum as i mention previously AND is effected by gravitational pull. therefore a mechanical waveform as well....

holy crap! did i say all that?!!!
 

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Like D-Man was saying, I have certain applications that i will use different gaps in different cyls, and to complicate things even more I have seen several instances of what worked the best on a dyno not give the best results on the track.

Jeff
Difference between the dyno load and a real world sustained load causing a lot more cylinder heat build-up. That's why a slightly fatter tune-up is typically faster in the real world vs what the dyno said makes the best power #'s..
 

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To me the cyl temp and plug heat range kinda go hand in hand.
Im sure I have complicated it even worse.



Jeff
No, you just opened anouther factor.

No you opened anouther can of worms!

Yes, Thats what you have done! HA HA!!!:yes::yes:
 

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No, you just opened anouther factor.

No you opened anouther can of worms!

Yes, Thats what you have done! HA HA!!!:yes::yes:

That ain't no kiddin..:devil:

Now for the loaded question....
What's a hot enough plug to stay clean under n/a conditions but not be too hot when the boost comes in..say 10 to 14#'s?? :D
Or worse yet, a 10:1 motor with 36# of boost, running Sunoco 118 fuel??:eek: Too much part throttle and idleing in the pits will kill a plug or two (fuel foul).. :confused:

Sometimes it's just impossible....and the only answer is change them often..:yes:
 

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Hi Veno.


Do you think the spark jumps at the speed of light?


I agree that typically a wider gap requires a higher level of coil saturation and thus a higher voltage spark.


In my opinion the issue can get kinda complicated by a lot of factors. I have seen where just changing a camshaft design will alter flame travel enough to require a different plug gap.


Like D-Man was saying, I have certain applications that i will use different gaps in different cyls, and to complicate things even more I have seen several instances of what worked the best on a dyno not give the best results on the track.



I guess in my uniformed view I see the spark plug and/or gap greatly influencing the "effective" timing of air/fuel ignition.


One of the major drawbacks to larger than needed gaps on a high compression, high rpm engine (again in my opinion) is that it is much harder to jump the gap the higher the cyl pressure is, and this can cause a high speed misfire or worse.


To me the cyl temp and plug heat range kinda go hand in hand.


Like I said, in my opinion its kind of complicated and Im sure I have complicated it even worse.



Jeff

Agreed Jeff
just pointing out distance related and time span required.. most of the time when gaps are opened.. the same plug is used increasing the heat on the plug.. a colder plug should be used to off set the increase in heat.

Yes electricity travels at the speed of light in a vacuum... in a cylinder where artificial atmosphere is introduced it slows some.. but not to the degree of early ignition which is what Al is pointing out ... and it would be early base on AL's findings... in stead of late based on the conditions in the cylinder.

based on the artificial atmosphere of the cylinder the spark would be late... wouldn't it?

Jeff I agree with your findings and observations.... I just wanted to point out that spark did not slow down to a measurable difference in the .013 difference in gap. and that the time in travel would not be so great that it would create detonation by lengthing the duration.. the spark would have a tendency to create late ignition rather than pre-ignition. wouldn't it?

i would think this would not be the case!
we are more concerned with the speed of the heat wave,not light. heat has a much slower speed than light.

heat is a mechanical waveform.(will not travel through a vacuum) light is a radiant waveform(will travel through a vacuum).

heat waveform is effected by density(compression) so the spark gap has a significant effect.

on a sidenote:

light is a very special waveform!! it is actually BOTH radiant and mechanical....

it will travel through a vacuum as i mention previously AND is effected by gravitational pull. therefore a mechanical waveform as well....

holy crap! did i say all that?!!!
you have to agree that a spark is electricity and not light... tho both travel at the same speed in a vacuum... right? the spark and heat generated by the spark is a byproduct of the arc...and its amperage.... amperage is the heat.... the voltage is ability to make the jump, amperage is the force behind the jump.... 10 volts with 500 amps will not jump very far. but 10,000 volts with only .45 mili amps can jump a good bit farther....

Static electricity is a good example of this.. not much amperage by high voltage... if mere light could ignite combustion gases then spark gaps and spark plugs would be irrelevant.
 

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Agreed Jeff
just pointing out distance related and time span required.. most of the time when gaps are opened.. the same plug is used increasing the heat on the plug.. a colder plug should be used to off set the increase in heat.

Yes electricity travels at the speed of light in a vacuum... in a cylinder where artificial atmosphere is introduced it slows some.. but not to the degree of early ignition which is what Al is pointing out ... and it would be early base on AL's findings... in stead of late based on the conditions in the cylinder.

based on the artificial atmosphere of the cylinder the spark would be late... wouldn't it?

Jeff I agree with your findings and observations.... I just wanted to point out that spark did not slow down to a measurable difference in the .013 difference in gap. and that the time in travel would not be so great that it would create detonation by lengthing the duration.. the spark would have a tendency to create late ignition rather than pre-ignition. wouldn't it?



you have to agree that a spark is electricity and not light... tho both travel at the same speed in a vacuum... right? the spark and heat generated by the spark is a byproduct of the arc...and its amperage.... amperage is the heat.... the voltage is ability to make the jump, amperage is the force behind the jump.... 10 volts with 500 amps will not jump very far. but 10,000 volts with only .45 mili amps can jump a good bit farther....

Static electricity is a good example of this.. not much amperage by high voltage... if mere light could ignite combustion gases then spark gaps and spark plugs would be irrelevant.

Veno, I know so little about this stuff, and what I do "think" I know is very badly corrupted with aging, Im not sure of anything!


Will a spark jump n a perfect vacuum?


And Im not sure that the speed a spark travels is even close to the speed of electricity/light, but it may well be.

I would think you could accurately measure the time difference in plug gaps with a good oscilloscope, but again I may b way off base.

As far as the dyno/track deal goes, I just don't think that a "typical" dyno will accurately simulate the different acceleration curves that a typical drag car sees on a pass. And in my opinion the rate that that an engine has the "capability" to accelerate is a very big factor in determining a proper ignition timing.


I have to be honest with you D-Man I wouldn't have a clue about plug ranges for a supercharged application, I would have to call somebody, that could help me. Like 1-888- pick a plug:)
 

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Ok, Veno think about this.

Plug reading are taken at WOT!

So lets just take a Engine turning 7500rpm.

Thats 7500 rpm = 125rps

125rps = 62.5 ignitions PS

Thats 360 degree rations x 62.5 rotations per second.

And we are dealing with only .01 degree of the rotation!

So thats 62.5 x 360 = 22500 degrees of measurement per second.

And we are dealing with .01 degree of ignition time.

So we take 22500 and X the 10th power = 225000

So we take 0.1 second and divide by 225000=
.44444444444444444444444444444444e-8 millisecond per fire at the plug.

So do you think that time is not relevant?

This is when theory of time collides with actual mechanical measured time.

And it is a fact it makes a difference.






10 microseconds: 1/100000 second
100 microseconds: 1/10000 second
1 millisecond ms: 10-3 = 1/1000 second = 0.001 s
1 centisecond cs: 1/100 second = 0.01 s
1 decisecond ds: 1/10 second = 0.1 s
• • • 1 second s: 1 second • • • reference
 

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Ok, Veno think about this.

Plug reading are taken at WOT!

So lets just take a Engine turning 7500rpm.

Thats 7500 rpm = 125rps

125rps = 62.5 ignitions PS

Thats 360 degree rations x 62.5 rotations per second.

And we are dealing with only .01 degree of the rotation!

So thats 62.5 x 360 = 22500 degrees of measurement per second.

And we are dealing with .01 degree of ignition time.

So we take 22500 and X the 10th power = 225000

So we take 0.1 second and divide by 225000=
.44444444444444444444444444444444e-8 millisecond per fire at the plug.

So do you think that time is not relevant?

This is when theory of time collides with actual mechanical measured time.

And it is a fact it makes a difference.






10 microseconds: 1/100000 second
100 microseconds: 1/10000 second
1 millisecond ms: 10-3 = 1/1000 second = 0.001 s
1 centisecond cs: 1/100 second = 0.01 s
1 decisecond ds: 1/10 second = 0.1 s
• • • 1 second s: 1 second • • • reference
Al, I think I am confused. Are you saying that is the speed of the ignition?

Or spark?

Or is it just time of cycle at 7500 rpm.

The spark surly isn't the same as the cycle time is it?



Jeff
 

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OK Al

186,000 miles per sec. X 5280 feet" = 982,080,000.00 ft per sec.

982,080,000.00 ft per sec. X 12 = 1,178,496,000.00 inches per sec.

1,178,496,000.00 inches per sec. X 10= 11,784,960,000.00 per .10 inch per sec.

11,784,960,000.00 per .10 inch per sec. X 10 = 117,849,600,000.00 per .010 inch per sec.

or am I all screwed up here
 

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Al, I think I am confused. Are you saying that is the speed of the ignition?

Or spark?

Or is it just time of cycle at 7500 rpm.

The spark surly isn't the same as the cycle time is it?



Jeff
I just showing when the plug fires in relation to the power cycle of the engine. It has a great effect in such a small amount of time.

And how it plays in time to the effect of the performance of the engine.

Moving the timing in milliseconds in the engine power cycle has great effects. And even as small in time the spark plug fires is relative. It's a mechanical proven fact.

If it was not, what would it matter what we set the plugs at.

Veno's point is the gap is irrelevant, based on how fast the energy crosses the plug gap.
 
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