Spark plug questions

[OregonNed]

I’m looking at changing plugs in my truck. Mine has the original 327 motor with stock heads, a mild cam, Pertronix ignition and headers. I’ve been using the Accel shorty plugs with .375 reach. Since I tend to over analyze things, I have a few questions. Would it make sense to pick a model of plug with a deeper reach? Will that work with my set up? summits “will it fit filter”recommends the .375 reach, but I want to make sure I get the best performing plug size. I also wonder what the plug gap should be for my non points ignition. Pretty sure the last one were set to .035. Would a wider gap be preferred? Really appreciate the advice. Thank you.

[conoco]

I have the shorties on my 350 and they are gapped at .45. They were gapped at .35 after reading a couple different forums more people were at .45. My truck is noticeably different for the better at .45. You wouldnt think it would make that big of a difference but it very much does. I had to go with shorties because I was sick of taking the passenger side header off every time I wanted to change or look at the plugs.

[OregonNed]

Originally Posted by conoco

I have the shorties on my 350 and they are gapped at .45. They were gapped at .35 after reading a couple different forums more people were at .45. My truck is noticeably different for the better at .45. You wouldnt think it would make that big of a difference but it very much does. I had to go with shorties because I was sick of taking the passenger side header off every time I wanted to change or look at the plugs.

That is good info. Thank you

[chevy71super]

With an MSD ignition & box I increased the plug gap to .45 as well. I haven't driven it that much since the change but it idles and runs really nice and smooth.

['68OrangeSunshine]

Points:......035
HEI +
Pertronix:..045

[OregonNed]

Thanks guys for the advice. I also checked the Pertronix site too in their FaQs

[RustyPile]

The "shorty" designation refers to the overall porcelain length not the thread reach. That can be changed.. Your heads have the 3/8th inch thread reach and that dimension cannot be changed. If a long reach plug is installed where a short reach is called for, the piston will strike the plug and severe internal engine damage is the result.. The head design determines the plug type, i.e. head to plug seal design.. There are two seal designs -- gasket ring or tapered seat.. Your heads are the early ring gasket type.. Again, that cannot be changed. The ignition system type determines the plug gap.. Common points type plugs should be gapped at .035 - .040.. HEI ignitions can be gapped .040 - .060, depending on coil output.. A wider gap allows the coil to "build voltage" to a higher number before the spark finally jumps the gap... If the gap is wider than the coil can handle, it can lead to premature coil failure.. Also the spark (voltage) sees the gap as resistance and can possibly seek other routes to ground. You've probably heard the saying, "electricity seeks the path of least resistance"??. Arc pathways can form inside the cap and or rotor to ground.. These paths are the carbon tracks found when a cap or rotor has failed..

Heat range is another factor to consider when selecting sparkplugs.. Thankfully, the engineers have this figured out for us.. In a "stone stock" engine, go with the factory recommendation.. Reading spark plugs in modified engines is becoming a lost art - something a rank beginner has to master.. The heat range can't be "pulled out of thin air".. Reading a used spark plug goes a long way toward selecting the proper heat range..

[OregonNed]

Thank you for the detailed information. Very helpful. This is such a great forum for information.

[kaycee]

What headers you run ? I have a set of Hedmans on my 327 and a regular plug is all I need AC/Delco R45S

[geezer#99]

[quote=RustyPile;8835153]The "shorty" designation refers to the overall porcelain length not the thread reach. That can be changed.. Your heads have the 3/8th inch thread reach and that dimension cannot be changed. If a long reach plug is installed where a short reach is called for, the piston will strike the plug and severe internal engine damage is the result.. The head design determines the plug type, i.e. head to plug seal design.. There are two seal designs -- gasket ring or tapered seat.. Your heads are the early ring gasket type.. Again, that cannot be changed. The ignition system type determines the plug gap.. Common points type plugs should be gapped at .035 - .040.. HEI ignitions can be gapped .040 - .060, depending on coil output.. A wider gap allows the coil to "build voltage" to a higher number before the spark finally jumps the gap... If the gap is wider than the coil can handle, it can lead to premature coil failure.. Also the spark (voltage) sees the gap as resistance and can possibly seek other routes to ground. You've probably heard the saying, "electricity seeks the path of least resistance"??. Arc pathways can form inside the cap and or rotor to ground..




A bit wide on the points rusty.
Normally .016 to .019.

Oops! Senior moment!
Correct that.
‘‘Twas thinking points gap, not plug gap!

[OregonNed]

Originally Posted by kaycee

What headers you run ? I have a set of Hedmans on my 327 and a regular plug is all I need AC/Delco R45S

Very cheap long tube headers. Unsure of brand. Number 1 and 6 have too little room for a socket. I’m getting either a snap on specialty socket or another set I found to get them off. I hate pulling the headers loose and then having to replace the gaskets.

[geezer#99]

For hard to get at plugs I’ve used some of these.


https://www.amazon.ca/TEKTON-2580-8-...65070544&psc=1

Or one of these.


https://www.zoro.com/westward-box-en...93/i/G1907701/

[RustyPile]

Originally Posted by geezer#99

A bit wide on the points rusty.
Normally .016 to .019.

Oops! Senior moment!
Correct that.
‘‘Twas thinking points gap, not plug gap!

That's OK geezer, I understand.. I have those "moments" too..