Plug gaps, small or big?

[69ss]

I was always told if you have a good ignition, the bigger the plug gap the better. I have mine set at .050 which is what my ignition instructions said to use. I have a 10.7to1 aluminum headed 496bbc with hyd roller and performance dist HEI and run 93 octane fuel. The engine runs good and never misses a beat but I have been lurking on some other forums and read these big gaps are not necessary. Here is what I read from another forum. I have alot of faith in what this person says and feel he is correct but all I have ever read before is the bigger the gap the better. What do you guys feel is correct in your opinion?

I am a huge advocate of not running large gaps in perfromance deals
They do nothing except,,,
They will tend to fire a very lean mixture which is harder to get started
GM ran large gaps for one sole purpose
To fire stupid lean mixtures in low compression engines that were far from efficient & had very little cylinder pressure compared to a performance engine.
In my opinion wide gaps have no place in a higher compression performance oriented engine & are a misfire waiting to happen as cylinder pressures go up.
I have never seen any power in the .045+ gaps recommended by some
I have never seen any loss of power at .030-.035
A Vertex mag uses .020 & less with no issues in some pretty stout deals
This whole wide gap idea is again in my opinion another example of monkey see, monkey do... print it in enough magazines it must be true crap
It has it's place but I do not feel this place is in performance engines.

Here is another quote that I found about the small gap theory.

Voltage rating (KV) of the coil is what the coil is capable of, not what it fires each strike.
Voltage requirements rise from, heat... pressure... and gap
Increase any of the 3 variables and the KV required to fire increases.
An engine at a 150 BMEP load requires about 20 to 22 KV to fire a .025 gold-palladium gap versus same engine at .015 gap takes about 15 KV. I know this from systems I have worked on at work, not play. With real-time firing KV on display.
My engine theoretically sees 216BMEP. I figger .025 gap is all the risk of misfire I want at 8000rpm and 216BMEP. Hard to alter the heat, and the pressure is what we are after, therefore gap is all I can really control.
Just me

[beaker60]

I've read pros,,and cons on this subject,,,I've been told by several really good builders,that if you have the voltage,you're better off running wider gaps,,,and then by other great builders,,"never go over .035",,,so I'm not sure what to believe.I can tell you this,,,and again,,it might have been my imagination,,but it always seems like,,I have a more consistant run,,using narrow gaps,,it seemed like with the wider gaps,,,I lost a little power.What i have started doing is running .040 gap,,it's sorta a give and take approach,,I have the voltage to jump .050,,,but at the same time,,and I'm not sure if this is true either,,,,,why make the igniton system work any harder than it needs to,,I figure .040 is right in between,,and it works for me,,,so I guess,it's left up to you to see what works best for you.

[dieselgeek]

No mention of the distributor gap? odd.


Things change with distributorless ignition. The distributor gap - and distributor phasing - play a large part in how the ignition system works (or doesnt).

[vincenelson]

Increasing the gap on the plug increases the resistance across the plug. This increases the volatage required to fire the plug. Also increasing fuel charge and load on the engine also increases the resistance, and the voltage required to fire the plug. Anytime the resistance increases the voltage must increase to ionize the gases across the gap. The thing to remember is ELECTRICTY IS A LAZY TEENAGER....it likes to take short cuts home and do as little work as possible. When the gap becomes too high in resistance the chances of firing the gap vers taking a short cut home becomes the problem. Leaking plug wires, traveling down the side of the insulator, jumping to another terminal in the distributor becomes a real problem. RPM also reduces the dwell time of the coil charging which also reduces the total amount of energy your ingition system is able to produce. .030 to .035 is a safe measurment to fire a plug and produce good heat energy to fire the cylindar with a good electronic ingition system.

[joedoozer]

I have wondered this as well. I have never posted the questions because.......we all know how forums can be. The fear of the "you are a dumb a$$ and shouldn't be racing if you can't gap a spark plug response". Every thread has one, and in most cases it kills the thread or turns into a bickering contest.

I have a 10:1 iron head 350 on pump gas. MSD 6AL ignition, nothing fancy. MSD says to gap them big for lower compressions, .055 I think (just guessing here). At the time I was running AR134's for plugs. They have an open style gap, the ground electrode doesn't shield the center electrode. So when I tried to gap it at .055 it looked very strange. Because the ground electrode was so short, it was pointing upward at such a large gap. I spent most of the season running those plugs at .035 and had no problems. It made good power and the plugs looked great. I now run NGK's that have a normal ground electrode and have gone to .045 gap. I haven't noticed any changes in performance or plug readings. I get the same performance from the NGk's as the Autolites at half the price.

[69ss]

[quote="joedoozer"]I have wondered this as well. I have never posted the questions because.......we all know how forums can be. The fear of the "you are a dumb a$$ and shouldn't be racing if you can't gap a spark plug response". Every thread has one, and in most cases it kills the thread or turns into a bickering contest.

I understand completely. So from what I'm reading on here, everyone thinks the smaller is less stress on the ignition and will get the job done. It makes sence to me. Thanks for your replies!

[vincenelson]

Nice car!!

[bigjoe1]

I have been dyno testing for over 40 years. The ONLY time I have ever seen plug gap make any difference is when you make it BIGGER.. I one instance, I got a 22 horsepower INCREASE by going to an 080 gap, from a 035 gap. I will admit, that is a real big difference, but I have had several guys tell me that the big gap was a big HP increase. I always run them at 055 to 060 in my serious race engines- The big gain was on a 990 HP big block, and the engine just would not make over the 1000 HP number.. When I did this, it was a really big deal, to make 1012 HP


JOE SHERMAN RACING

[dieselgeek]

I have been dyno testing for over 40 years. The ONLY time I have ever seen plug gap make any difference is when you make it BIGGER.. I one instance, I got a 22 horsepower INCREASE by going to an 080 gap, from a 035 gap. I will admit, that is a real big difference, but I have had several guys tell me that the big gap was a big HP increase. I always run them at 055 to 060 in my serious race engines- The big gain was on a 990 HP big block, and the engine just would not make over the 1000 HP number.. When I did this, it was a really big deal, to make 1012 HP


JOE SHERMAN RACING

So doesn't that mean that you cured a misfire problem? I've tested gap differences in engines from 200hp all the way up to 1800+ and the only time changes to the ignition system involved power gains was when I was fixing a rather glaring misfire issue.

[bigjoe1]

There was NO miss fire involved in both cases.. It just made more HP , plain and simple.


JOE SHERMAN RACING

[dieselgeek]

There was NO miss fire involved in both cases.. It just made more HP , plain and simple.


JOE SHERMAN RACING

Were you monitoring AFRs in each cylinder to know for sure? Perhaps you cured a misfire that you weren't hearing?

[smeg]

I have tried bigger gaps in lots of engines and have always made more tq and hp with around .033". Tried .040" to .050"" and always made more going back down. This was with MSD and ICE systems.
But I have never tried .060" plus, so I will give that a go when I can.

[MadBill]

I have been dyno testing for over 40 years. The ONLY time I have ever seen plug gap make any difference is when you make it BIGGER.. I one instance, I got a 22 horsepower INCREASE by going to an 080 gap, from a 035 gap. I will admit, that is a real big difference, but I have had several guys tell me that the big gap was a big HP increase. I always run them at 055 to 060 in my serious race engines- The big gain was on a 990 HP big block, and the engine just would not make over the 1000 HP number.. When I did this, it was a really big deal, to make 1012 HP


JOE SHERMAN RACING

So doesn't that mean that you cured a misfire problem? I've tested gap differences in engines from 200hp all the way up to 1800+ and the only time changes to the ignition system involved power gains was when I was fixing a rather glaring misfire issue.

I've had engines miss at light throttle due to accidentally tiny gaps (~0.010) but there's no way you can cure a misfire by going up from a large gap to a huge one...

[dieselgeek]

I have been dyno testing for over 40 years. The ONLY time I have ever seen plug gap make any difference is when you make it BIGGER.. I one instance, I got a 22 horsepower INCREASE by going to an 080 gap, from a 035 gap. I will admit, that is a real big difference, but I have had several guys tell me that the big gap was a big HP increase. I always run them at 055 to 060 in my serious race engines- The big gain was on a 990 HP big block, and the engine just would not make over the 1000 HP number.. When I did this, it was a really big deal, to make 1012 HP


JOE SHERMAN RACING

So doesn't that mean that you cured a misfire problem? I've tested gap differences in engines from 200hp all the way up to 1800+ and the only time changes to the ignition system involved power gains was when I was fixing a rather glaring misfire issue.

There's no way you can cure a misfire by going up from a large gap to a huge one...

Stranger things have happened.

But I highly doubt such large gains from something as simple as "opening up a plug gap" - EVERY dyno tuner I know, if they had this happen, would immediately stop their testing and go back to the narrower gap, to PROVE that what they believe is happening, is what's really happening. This kind of stuff doesn't just "happen" in a modern engine development program.

When I hear someone say "We picked up XX big hp numbers by increasing the gap (or changing to Magic Brand plugs)" and they DON'T immediately follow that up with a backup run to prove their "findings" - then I pretty much know that this person is missing something else entirely, And at this point, who knows what other large power gains their questionable testing and tuning approach is leaving on the table?

[JWebb]

During my younger years of Karting, we did lots of dyno testing, and those engines would always show gains from HUGE gaps, and would actually continue to increase until the magneto just couldn't jump the gap. At the end we were cutting 2/3 of the ground strap off and running .090" gaps.

It is kind of an apples to oranges comparison though.