Another Spark Plug Gap Thread.... LOL

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Vbb199

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Im in Alabama.


Ah ok.
Well if youre ever this way, have a beer.
And likewise, ill contact you, 1 beer for each hand, maybe 1 in my pocket.
 

Swearbody

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Im in Alabama.

Have you ever been to Legget NC. My uncle was the mayor before he got mudered during a home invasion. They just sentenced the fuckers to life...should have just brought them here to me.
 

Vbb199

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Have you ever been to Legget NC. My uncle was the mayor before he got mudered during a home invasion. They just sentenced the fuckers to life...should have just brought them here to me.


I have not, no. Thats pretty ****** up
 

Swearbody

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I have not, no. Thats pretty ****** up

Yep. Best most humble Christian man ive ever known. He and my aunt were lost to a few crackheads. Thought you may have seen it in the news since he was a mayor in NC bu it happened over a year ago. Fuckers tried to fight it in court. ******* fuckers ******* ****....
 

fast68chevy

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30k secondary voltage is very low.. HEI is 50 to 60k your gap for HE needs to be .045 for the ordinary normal common stock ac delco R series plugs. R45 TS or TSX is what i run in all my old v8 carb motors. a litle extra reach of the tip into the chambers for easier better starts and smoother runing better ignition.. and
there are also extended tip plugs for the oil burners etc.
 

QBuff02

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.060 over 454, balanced and blueprinted, Cast Iron 049 heads, hardened exhaust seats installed, heads machined down to 115cc chambers, 2.190 intake 1.880 exhaust valves installed, some proprietary bowl and port work, 10.25:1 compression, squared block and pistons are .005 below deck, .040 compressed thickness head gaskets, for .045 quench, semi custom ground cam installed on 106 centerline, full MSD ignition, NGK V-power 7 plugs, 16 degrees initial timing, running 110 octane. Started at .040 gap, seemed to run ok, but based off the ignition recommendations and the engine shop recommendations, increased gap by .010 in increments, found that my best starting hot or cold and cleanest running of the engine (smell of exhaust and response of engine) was when I got the plugs gapped at .065. It has lived just like that for over 2 years now with zero issues and happy motoring. Remember, voltage requirement is directly proportional to the gap size. The larger the gap, the more voltage is needed to jump the gap. Most tuners know that increasing the gap size increases the spark area to the air-fuel mixture, which maximizes efficiency. For that reason, most people add high-energy ignition systems. The added energy allows you to increase the gap yes, but still have enough voltage to jump the gap for a cleaner burn. Many think that the larger the gap, the better but on the back side of that, if the gap is too large, and the ignition system isn't capable enough or hot enough to provide the voltage needed to spark across the gap of the plug, or turbulence in the combustion chamber blows out the spark it will cause issues. Also why when you get to 12:1 and above or start using forced induction systems you start narrowing the gap back down on the spark plugs to the .035-.040 range, as turbulence and cylinder pressures can and will have a tendency to blow out the spark. But a hotter ignition will also combat this effect as well with tighter gaps. I would have never believed the wider gap on my engine until I experimented with it but it seems to work quite well in my application and I've been north of 6,000rpm many times with clean plugs and no detonation issues.
 
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Vbb199

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.060 over 454, balanced and blueprinted, Cast Iron 049 heads, hardened exhaust seats installed, heads machined down to 115cc chambers, 2.190 intake 1.880 exhaust valves installed, some proprietary bowl and port work, 10.25:1 compression, squared block and pistons are .005 below deck, semi custom ground cam installed on 106 centerline, full MSD ignition, NGK V-power 7 plugs, 16 degrees initial timing, running 110 octane. Started at .040 gap, seemed to run ok, but based off the ignition recommendations and the engine shop recommendations, increased gap by .010 in increments, found that my best starting hot or cold and cleanest running of the engine (smell of exhaust and response of engine) was when I got the plugs gapped at .065. It has lived just like that for over 2 years now with zero issues and happy motoring. Remember, voltage requirement is directly proportional to the gap size. The larger the gap, the more voltage is needed to jump the gap. Most tuners know that increasing the gap size increases the spark area to the air-fuel mixture, which maximizes efficiency. For that reason, most people add high-energy ignition systems. The added energy allows you to increase the gap yes, but still have enough voltage to jump the gap for a cleaner burn. Many think that the larger the gap, the better but on the back side of that, if the gap is too large, and the ignition system isn't capable enough or hot enough to provide the voltage needed to spark across the gap of the plug, or turbulence in the combustion chamber blows out the spark it will cause issues. Also why when you get to 12:1 and above or start using forced induction systems you start narrowing the gap back down on the spark plugs to the .035-.040 range, as turbulence and cylinder pressures can and will have a tendency to blow out the spark. But a hotter ignition will also combat this effect as well with tighter gaps. I would have never believed the wider gap on my engine until I experimented with it but it seems to work quite well in my application and I've been north of 6,000rpm many times with clean plugs and no detonation issues.


Hey thanks for the info!!

After i gapped mine to .060 from a .045 with the apparent "weak" 30k coil and ignition box, my performance noticably increased, while my cam kinda drops at 4500-5,000 theres no misfires or issues all the way thru the range.
Was a good mod. I was just getting collective ideas on everyones setups.

Was toying with the idea of a smaller gap, but i think ill leave it.
 

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Found some more interesting reading. A bit long but makes good sense:

https://www.badasscars.com/index.cf...duct_id=73/category_id=58/mode=prod/prd73.htm

What dictates the width of a spark plug gap is both the amount of voltage and amperage of your ignition system as well as cylinder pressure and air / fuel mixture density. The rule of thumb is that the more power an engine makes, the smaller the gap needs to be. Race engines (contrary to popular belief) use smaller gaps than most "stock" engines do because of higher cylinder pressures and denser air/fuel mixtures. This is because a small, intense spark is better for lighting a highly dense, very wet fuel mixture like you'll find in high powered race or performance engines, kind of like these new lighters you see these days with a small, intense blue flame. They light cigars, fires, etc., better in the rain or wind where a weak yellow flame that you get from a match or a typical Bic type lighter isn't as hot and easily blows out.

A smaller gap will yield a short, intense spark and will usually make the engine real responsive. A wide gap creates a longer spark arc but without sufficient "juice" from your ignition system, (including amps), it can be weak and yellow in color. So a small intense spark is much better than a big, weak spark, especially when dealing with richer fuel mixtures and more volumes of fuel being burned.

A good starting point and pretty much the all around best gap is .035". If you want to experiment to see what works best for your particular engine, ignition system, etc., then try going up to .040" and then .045", noting each time how the engine idles, responds, and pulls to your max RPM. Once you've gone bigger on the gaps, now try going smaller to .032", .030" and .025", and again, note how the engine runs. Whatever the gap was when the engine ran it's best overall, is where you should gap your plugs at.

Just an FYI; most very high powered blown gas, blown alcohol, and even blown fuelers run gaps as small as .026" (give or take) and use ignition systems that use 50,000 - 80,000 volts, but more importantly, up to 40 Amps! Amps are what kill you when you get shocked. Stun guns have up to 1 million volts, but no amps so they aren't lethal. Hell, static electricity you get when you shock yourself against a door knob or your car door can be upwards of 100,000 Volts or more, but does it kill you? Nope. Your house electrical current can kill you too, but it's only 110 Volts, BUT it has 15 - 20 Amps pushing that Voltage behind it. Get hit by your house's 220 Volt system are you will most likely die. Not because of the 220 Volts. Again, it isn't Volts that kill you (think of a stun gun), it's Amps. Most 220 Volt outlets are for running heavier equipment such as your dryer, a welder, etc., and have between 20 - 50 Amps behind them. That kind of current will light your ass up and fry you, but a 50,000 Volt jolt from a spark plug won't, unless you are screwing around with a serious ignition system like what a Top Alcohol or Fueler engine runs with 40 Amps behind them. They even have decals on the tops of the dual magnetos saying "Caution! Lethal Current".

Your ignition system may have lots of Voltage, but no Amperage. This is why even on high energy ignition systems, (CONTRARY to what their lame instructions say to gap your plugs at), you CLOSE the gap on engines making more power. Usually .035" is around the best gap, even though many instruction manuals say to open your gap to .045". Go ahead and try that, but when it doesn't run as good, or it drops cylinders at high RPM because that wider / weaker spark can't light the cylinders consistently, you'll know why. This gets even more true when you are running too rich and have too wet of a mixture. It's harder to light a fire in the rain than it is on a dry summer day. Inside your cylinder isn't much different.

On mild engines, (even you guys who have 400 - 550 HP), that isn't enough power to be concerned with on the gaps, and a gap of .045" will "probably" run just fine because you aren't burning enough fuel (a wet enough mixture) to cause cylinders to drop with a decent ignition system, but start getting over 600, 800, 1,000 horsepower and that .045" or so gap isn't going to work out too well. Either way, your milder engine WILL run better with .035" gaps instead of the .045" gaps that they tell you to run.

spark plug gaps
Now, while we're on the subject of gaps, a little extra trick you can do to your plugs is to do what's commonly called "side gapping" them. This is when you take a small file or a fine grinder to the ground strap and cut it back so it only covers about half of the center electrode. This exposes the spark to the open cylinder and combustion area more and prevents the shrouding that the full length ground strap tends to do on regular plugs. This can be worth a few extra horsepower, just as indexing a set of plugs is worth a few extra ponies. I have another tech tip on how to index spark plugs which can gain you a few extra "free" HP.

MY TIP: You can use one of these (LISLE 50850 IGNITION SPARK TESTER) and adjust it until you get a bright BLUE spark. Then measure the gap and set your plug gap accordingly. Do this for each plug since plug wire resistances vary slightly. It takes a while to complete this but should be worth it since it will give you a better indication of how well (or not well) your system is performing.
 

CoggedBelt75

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383 SB , 8:1, iron World Sportsman heads, belt driven intake, MSD 6 AL ignition box, MSD Blaster coil, MSD Boost Timing Master, MSD small cap dizzy, NGK UR6 plugs gapped at 33 (pulley change, 28), 93 octane no watered down pump gas
 

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