but its spread over all the links, if you can get that skill mastered your well ahead of most guys who fail to take the time and effort to learn that skill
guys frequently ask me what plug gap to use, Provided your ignition functions correctly and your using the correct heat range plugs and a reasonably close fuel/air ratio and timing advance, Ive never seen any improvements in gaps tighter or wider than .045.
Ive never seen any advantage to gaps over .045 and Ive seen plug gaps as wide as .060 or under .035 cause misfires with some ignitions in a FEW applications so after years of testing and racing I generally set plug gaps at .045, if your having issues with misses at .045 its not the plug gap thats the cause,its some other problem with your ignition or fuel/air ratio or ignition timing advance,high resistance ignition wire, moisture,a bad coil,loose connections, firing order or arcing ignition etc..
BTW some of the older guys will remember that the SBC used to have 13/16" spark plugs and they were changed to the smaller 5/8" style in the early 1970s, and if your wondering why they changed it was because they found that smaller diam. plug threads allowed slightly larger coolant passages and allowed moving the plug location slightly closer to the exhaust valve and also allowed a slightly changed angle all of which allowed lower emissions, better control on combustion and less chance of stripped or cross threading plugs.
post very clear pictures of your spark plugs, label the cylinder # they came from, and measure the fuel pressure you can tell a good deal if you know those factors and how to read plugs.
most engine misses are related to either fuel/air ratio changes or ignition, so the first step is isolate the problem, or the cause, it could be the timing, advance curve, fuel pressure , a vacuum leak,or a defective ignition etc, you need to do a few tests
http://www.harborfreight.com/3x-magnify ... 94367.html

having a spark plug holder with numbered holes and a good inspection tool helps

http://www.summitracing.com/parts/PIT-229/
Ive found its a whole lot faster to use a quality IR temp gun, to locate a individual cylinder that's mis-firing as it tends to run significantly cooler than adjacent cylinders, or hotter if its a vacuum leak at times, as lean F/A mixes tend to run hotter
(Ive used this one for years)

http://www.professionalequipment.com/ex ... ermometer/
Wide temperature range from -58 to 1832°F (-50 to 1000°C)
many temp guns don,t read high enough or accurately enough
http://www.professionalequipment.com/ex ... ermometer/
that you can use on the engine to check ALL 8 exhaust temps, individually, this quickly locates plugged injectors or vacuum leaks ETC
Wide temperature range from -58 to 1832°F
when selecting an IR gun for automotive use, you really want to be able to read from 0 F deg-about 1400F deg. to cover most conditions you'll test for
READ THRU LINKS AND SUB LINKS
http://www.4secondsflat.com/Spark_plug_reading.html
viewtopic.php?f=70&t=3949&p=25481#p25481
learning to correctly read plugs is a KEY FACTOR in learning how to tune and diagnose engine conditions, ignition temperatures,fuel/air ratios and detect detonation
example
Here is a link to AC Delco for information on the codes.
On the R45TSX for example:
R=resistor spark plug
45=heat range
T=tapered plug
S=extended tip
X=wide gap
http://www.acdelco.com/parts/sparkplugs ... cation.jsp

some reference chart info
http://www.sparkplug-crossreference.com ... ence8.html
http://www.spark-plugs.co.uk/pages/tech ... htm#ISOJIS
http://www.summitracing.com/parts/msd-3508
http://www.pcmforless.com/index.php?opt ... &Itemid=56
http://www.mirage-performance.com/tech/sparkplugs.html
http://go.mrgasket.com/pdf/sparkplugs/U ... erence.pdf
http://www.autorepairinstructions.com/?cat=7
viewtopic.php?f=70&t=9
http://www.kennedysdynotune.com/Spark%20Plug%20Tech.htm
IF your trying to tune an engine or track down a problem,When you inspect plugs ,pull all 8 plugs , drill some (8) 1/2 holes in 2 parallel lines in a 12"" section of 2"X6" wood and label the holes, to indicate the cylinders
2-4-6-8
1-3-5-7
so you can stick the porcelain ends , of each plug ,the wires snap onto, into the holes so you can photograph and inspect the tips and electrodes in clear detail as they can tell you a great deal about the engines running conditions
viewtopic.php?f=50&t=892&hilit=+socket
I frequently get asked what brand of plugs I use or suggest,
Ive had good luck with
AC DELCO
NGK
BOSCH PLATINUM plugs
most gapped at .043-.045
these are companys making a decent plug, your engine might run better with something else but Ive had good results with these brands
all work well in most LT1 and L98 chevy SB engines
just stick to the single electrode ground designs as in most cases Ive found the multi ground plugs cost more and don,t provide ANY improvement, and before you go linking in tests showing plug brand XYZ makes 5- 7 extra hp you should realize any decent experienced dyno operator can rig the results that much, either way at will, and if company xyz pays you several hundred dollars to show their plugs provide a small margin of extra power you can bet your butt the dyno operator will find it!
and when the next company ABC stops by for a TEST, you can bet they also show a small advantage
reading plugs can tell you a great deal, but if you don,t read thru and understand the linked info youll be at a big disadvantage heres a very useful chart, depicting plug conditions to look for indicating combustion chamber temp and air/fuel ratio indicators
http://www.4secondsflat.com/plug_chart.html
http://www.4secondsflat.com/Spark_plug_reading.html
http://www.dragstuff.com/techarticles/r ... plugs.html
http://www.custom-car.us/ignition/spark ... range.aspx
http://ngksparkplugs.com/tech_support/s ... p?mode=nml
http://www.autorepairinstructions.com/?cat=7
viewtopic.php?f=70&t=5428
http://www.power-21.com/AutolitePower21 ... preads.pdf
http://kb-silvolite.com/article.php?action=read&A_id=63
http://www.autohausaz.com/html/spark-pl ... wires.html
http://en.wikipedia.org/wiki/Spark_plug
http://www.ngksparkplugs.com/techinfo/s ... lation.asp

http://www.verrill.com/moto/sellingguid ... rchart.htm
http://www.strappe.com/plugs.html

cross reference
http://www.angelfire.com/extreme4/skido ... ERENCE.htm
viewtopic.php?f=50&t=1853&p=4848#p4848
QUOTE
"Heat range
The operating temperature of a spark plug is the actual physical temperature at the tip of the spark plug within the running engine. This is determined by a number of factors, but primarily the actual temperature within the combustion chamber. There is no direct relationship between the actual operating temperature of the spark plug and spark voltage. However, the level of torque currently being produced by the engine will strongly influence spark plug operating temperature because the maximum temperature and pressure occurs when the engine is operating near peak torque output (torque and RPM directly determine the power output). The temperature of the insulator responds to the thermal conditions it is exposed to in the combustion chamber but not vice versa. If the tip of the spark plug is too hot it can cause pre-ignition leading to detonation/knocking and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator causing a loss of spark energy or the actual shorting-out of the spark current.
A spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug. A spark plug is said to be "cold" if it can conduct more heat out of the spark plug tip and lower the tip's temperature. Whether a spark plug is "hot" or "cold" is known as the heat range of the spark plug. The heat range of a spark plug is typically specified as a number, with some manufacturers using ascending numbers for hotter plugs and others doing the opposite, using ascending numbers for colder plugs.
The heat range of a spark plug (i.e. in scientific terms its thermal conductivity characteristics) is affected by the construction of the spark plug: the types of materials used, the length of insulator and the surface area of the plug exposed within the combustion chamber. For normal use, the selection of a spark plug heat range is a balance between keeping the tip hot enough at idle to prevent fouling and cold enough at maximum power to prevent pre-ignition leading to engine knocking. By examining "hotter" and "cooler" spark plugs of the same manufacturer side by side, the principle involved can be very clearly seen; the cooler plugs have more substantial ceramic insulators filling the gap between the center electrode and the shell, effectively carrying off the heat, while the hotter plugs have less ceramic material, so that the tip is more isolated from the body of the plug and retains heat better.
Heat from the combustion chamber escapes through the exhaust gases, the side walls of the cylinder and the spark plug itself. The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature. A cold plug will not materially cool down an engine's running temperature. (Too hot of a plug may, however, indirectly lead to a runaway pre-ignition condition that can increase engine temperature.) Rather, the main effect of a "hot" or "cold" plug is to affect the temperature of the tip of the spark plug.
It was common before the modern era of computerized fuel injection to specify at least a couple of different heat ranges for plugs for an automobile engine; a hotter plug for cars which were mostly driven mildly around the city, and a colder plug for sustained high speed highway use. This practice has, however, largely become obsolete now that cars' fuel/air mixtures and cylinder temperatures are maintained within a narrow range, for purposes of limiting emissions. Racing engines, however, still benefit from picking a proper plug heat range. Very old racing engines will sometimes have two sets of plugs, one just for starting and another to be installed once the engine is warmed up, for actually driving the car."
learn how read the spark plugs their condition will tell you a good deal about cylinder burn conditions, get an IR temp gun,vacuum gauge and timing light they are a great tuning and diagnostic aid,as they can indicate problems like a clogged cat or faulty ignition, etc. don,t solely relie on a single indicator
http://www.strappe.com/plugs.html
http://performanceunlimited.com/illustrations/sparkplugs.html
http://www.dragstuff.com/techarticles/s ... rence.html
http://www.ngksparkplugs.com/techinfo/s ... country=US
the plugs are normally done (the electrodes cut back)with a dremel tool cutting disk




http://www.autorepairinstructions.com/?cat=7




heres a good indication of plugs running a bit rich at idle and real lean in the upper rpm range

keep in mind that different brands of plugs will have different lengths that can be critical with ignition wire to header clearances
http://www.centuryperformance.com/spark ... g-192.html
http://www.carcraft.com/techarticles/sp ... index.html
a few places to look for more info on plugs
http://www.centuryperformance.com/spark ... pg-26.html
http://www.dragstuff.com/techarticles/h ... plugs.html
http://www.youtube.com/watch?v=fiMM2S0aADM
http://opc.mr2oc.com/online_parts_catal ... _plugs.jpg
http://www.gofastzone.com/techtips/sparkplugs/sparkplugs.htm
http://www.ngksparkplugs.ca/documents/partnumberkey.pdf
http://www.autohausaz.com/html/spark-pl ... wires.html
http://www.acdelco.com/html/pi_plugs_ident.htm
http://www.autolite.com/framer.cgi?page=http://www.autolite.com/products/racing.htm
http://members.uia.net/pkelley2/sparkplugreading.html
http://www.circletrack.com/enginetech/c ... index.html
http://www.atlanticjetsports.com/_techtalk/00000005.htm
http://www.strappe.com/plugs.html
http://www.babcox.com/editorial/cm/cm59910.htm
http://www.4secondsflat.com/Spark_plug_reading.html
http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf
http://www.nightrider.com/biketech/spkplghnbook.htm
http://www.tsrsoftware.com/sparkplug.htm
viewtopic.php?f=70&t=1809&p=4671#p4671
http://www.gnttype.org/techarea/engine/plugs.html
http://www.dansmc.com/sparkplugs1.htm
http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp2.asp
http://www.pajjakid.com/ubipa/sparkplugs.htm
http://www.edelbrock.com/automotive/sparkplugs.html
http://www.bullittarchive.com/Maintenance/Sparkplugoverview/
http://www.powerarc.com/sparkplug.htm
http://www.carcraft.com/techarticles/64378/
http://www.wakularacing.com/TechnicalInfo.htm
viewtopic.php?f=55&t=109
http://www.geocities.com/MotorCity/Flats/3877/spark.html
viewtopic.php?f=44&t=773&p=1123#p1123
BTW IF YOU WANT TO AVOID ETHANOL LACED FUEL
http://pure-gas.org/