Gap in spark plugs?
Banned
Joined: May 2003
Posts: 6,661
From: LA (lower Alabama)
Re: Gap in spark plugs?
Originally Posted by BLinindoll
.050" is factory gap.
.050 gives ya a tad smoother idle and sells a lot of opti's and tune ups.
If the opti gets a little weak and can't jump .050 then the juice backs up in the cap and causes carbon tracking.Juice has to go somewhere.
Registered User
Joined: Apr 2004
Posts: 459
From: East Greenbush, NY
Re: Gap in spark plugs?
Well if the opti can't make the .050" gap then wouldn't you agree it's time for an opti anyway? If it were me, I would rather put in an opti if it needed it instead of squeezing some more life out of it. IMO if the opti can't do what the factory set it up to do, then it's time for a new one. If your muffler rotted out, would you pinch the exhaust pipe to quiet it down? No, you'de buy a new muffler. This is all JMO.
Last edited by BLinindoll; Apr 30, 2005 at 08:12 PM.
Banned
Joined: May 2003
Posts: 6,661
From: LA (lower Alabama)
Re: Gap in spark plugs?
Originally Posted by BLinindoll
Well if the opti can't make the .050" gap then wouldn't you agree it's time for an opti anyway? If it were me, I would rather put in an opti if it needed it instead of squeezing some more life out of it. IMO if the opti can't do what the factory set it up to do, then it's time for a new one. If your muffler rotted out, would you pinch the exhaust pipe to quiet it down? No, you'de buy a new muffler. This is all JMO.
If you know anything about DC electricity then you will understand why.
Would be a bit of stupidity to pinch an exhaust and don't run mufflers anyway.
Do you know why they narrow the gap in FI or NO2 cars,it's the same principal. It just makes damn sure the plug fires and the .050 adds nothing but a big bill down the road.
Registered User
Joined: Jul 1999
Posts: 1,041
From: Robinson, IL
Re: Gap in spark plugs?
I was getting ready to redo my plugs and was wondering if .050 was too much. I was thinking about .040 since I run an MSD D6. ANy others have a comment about the gap with OEM opti and also for those with an MSD box?
Registered User
Joined: Dec 1969
Posts: 27,730
From: Little Rock, AR
Re: Gap in spark plugs?
IMO, the only reason you would make the gap smaller is for special circumstances (forced induction, nitrous...). The stock system was designed with enough power to be able to jump the gap of .050". With an added MSD, you would certainly think it would have even less of a problem doing it. I always thought the bigger gap was an advantage. 
Banned
Joined: May 2003
Posts: 6,661
From: LA (lower Alabama)
Re: Gap in spark plugs?
Originally Posted by shoebox
IMO, the only reason you would make the gap smaller is for special circumstances (forced induction, nitrous...). The stock system was designed with enough power to be able to jump the gap of .050". With an added MSD, you would certainly think it would have even less of a problem doing it. I always thought the bigger gap was an advantage.
Just like FI cars.
Wider gaps came out when the smog laws came into effect.
Not saying wider won't work( it does as long as the opti and wires are in good enough shape to jump the gap) but your opti will last longer with narrower gaps.
Registered User
Joined: Dec 1969
Posts: 27,730
From: Little Rock, AR
Re: Gap in spark plugs?
If you are only worried about e.t.'s then you use whatever works for you. 
For a daily driver, the factory recommendations should work fine. From my understanding, it is in the upper rpms that a narrower spark gap may have a slight advantage.
For a daily driver, the factory recommendations should work fine. From my understanding, it is in the upper rpms that a narrower spark gap may have a slight advantage.
Registered User
Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
Re: Gap in spark plugs?
If you're using stock plugs then just run the stock gap. If you're using a plug that isn't necessarily made specifically for the engine, you need to run a gap that's more ideal for that plug.... probably .035-.040. Just check with the plug manufacturer.
One thing about it is... if you ARE running a more generic SBC plug, gapping it wide will cause the electrodes to be unparallel and you'll get some weird wear which could lead to problems.
-Mindgame
One thing about it is... if you ARE running a more generic SBC plug, gapping it wide will cause the electrodes to be unparallel and you'll get some weird wear which could lead to problems.
-Mindgame
Registered User
Joined: Jul 1999
Posts: 1,041
From: Robinson, IL
Re: Gap in spark plugs?
Originally Posted by Mindgame
If you're using stock plugs then just run the stock gap. If you're using a plug that isn't necessarily made specifically for the engine, you need to run a gap that's more ideal for that plug.... probably .035-.040. Just check with the plug manufacturer.
One thing about it is... if you ARE running a more generic SBC plug, gapping it wide will cause the electrodes to be unparallel and you'll get some weird wear which could lead to problems.
-Mindgame
One thing about it is... if you ARE running a more generic SBC plug, gapping it wide will cause the electrodes to be unparallel and you'll get some weird wear which could lead to problems.
-Mindgame
How do you define "more generic SBC plug"? A copper? I am about to install a set of NGK iridium plugs (listed for an LT1). I am sure they don't make the generic list. Any recommendations on a gap for this plug with my mods? BTW, I changed wifey's Lexus RX300 oem iridium plugs at 112k miles. I was amazed that all six held the oem recommended gap with all those miles.
Registered User
Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
Re: Gap in spark plugs?
From NGK's website:
I'm not an NGK user so I can't speak from personal experience.
I do use Champion and Champion has a # designation (believe it's the last #) which tells you whether the plug is a "wide gap" plug or not. Factory plugs tend to be of the "wide gap" variety, mainly for emissions reasons. If I were running a Platinum factory type plug I would probably stay closer to the factory spec but my first try would be to run them at .040. If they run fine there, then just gap them that way every time you use that plug.
As the NGK advice insinuates... there are lots of variables. LR's advice is based around running a spark plug in an engine making ~150hp more than stock. How many people are in that boat or better?
Personally... I've always had great results running gaps in that range.
So don't rule it out. You'll have to try it for yourself.
If the car runs well with a tighter gap then so be it. The gap will open up over time (precious metal & iridium plugs less than others) and that does work the ignition system harder. Aftermarket boxes and hotter coils... well maybe a little wider. Just depends.
On a side note, there are other ways to get a better spark kernel. Different types of electrodes like the thin wire type work well for that, although they don't last as long.
-Mindgame
Frequently Asked Questions
Q: Do I need to set the "gap" when installing a new set of plugs?
A: Maybe. A spark plug part number might fit hundreds of engines and, although the factory will typically set the gap to a pre-selected setting, this may not be the right gap for your particular engine. Insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy. It is always best to check the gap against the manufacturer's specifications.
Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology) you can open the gap from .002-.005".
If you have any questions, please contact the NGK Sparkplugs Tech Staff here. The manufacturer of your vehicle, the company that produced the aftermarket products you've used and/or your mechanic are all additional sources of gapping information if you've modified your vehicle.
Q: Do I need to set the "gap" when installing a new set of plugs?
A: Maybe. A spark plug part number might fit hundreds of engines and, although the factory will typically set the gap to a pre-selected setting, this may not be the right gap for your particular engine. Insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy. It is always best to check the gap against the manufacturer's specifications.
Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology) you can open the gap from .002-.005".
If you have any questions, please contact the NGK Sparkplugs Tech Staff here. The manufacturer of your vehicle, the company that produced the aftermarket products you've used and/or your mechanic are all additional sources of gapping information if you've modified your vehicle.
I do use Champion and Champion has a # designation (believe it's the last #) which tells you whether the plug is a "wide gap" plug or not. Factory plugs tend to be of the "wide gap" variety, mainly for emissions reasons. If I were running a Platinum factory type plug I would probably stay closer to the factory spec but my first try would be to run them at .040. If they run fine there, then just gap them that way every time you use that plug.
As the NGK advice insinuates... there are lots of variables. LR's advice is based around running a spark plug in an engine making ~150hp more than stock. How many people are in that boat or better?
Personally... I've always had great results running gaps in that range.
So don't rule it out. You'll have to try it for yourself.
If the car runs well with a tighter gap then so be it. The gap will open up over time (precious metal & iridium plugs less than others) and that does work the ignition system harder. Aftermarket boxes and hotter coils... well maybe a little wider. Just depends.
On a side note, there are other ways to get a better spark kernel. Different types of electrodes like the thin wire type work well for that, although they don't last as long.
-Mindgame
Registered User
Joined: Aug 2000
Posts: 146
From: Sterling Hgts, Mich
Re: Gap in spark plugs?
my crapidfires are gaped at .060,and i spin my motor way up to 6700rpm!!!,,(holycrap!!!! 5years later and it still runs,stock bottomend,and 10bolt rear,NO BULL**** HERE) 