I gave you actual facts and you referred to them as old wives tales, when in actuality, you couldn't relate to what I said. Getting in to a pizzing contest with you ( and close minded people like you )is a waste of MY time. BTW, fuel cars do run a tight plug gap - but IT'S THE LARGEST GAP THEY CAN GET AWAY WITH! Light bulb come on yet???

I use .035... I did try larger but it didnt do
anything.. as said already.. a large gap is load
on the ignition system which can break stuff

.035 here MSD 6 AL, Blaster coil, firecore wires, NGK plug

I will say it one last time. You wanna run the largest gap you can get away with AND STILL BE ABLE TO LIGHT THE PLUGS - what ever that # might be. In your case, it was probably .035" I have an ignition system that is easily capable of 55K+ open voltage. Seen it on a scope. I run lots of boost - 21 psi in the lights. I also spray some water. Can't run gaps wider than .030" in that application. Ran the same ignition in a NA motor I was running. Could easily run .045 gap with no problem - and I did! In that application, why would I want to run a plug gap of .030"??? For more HP??? No way! Like everything else we do with race engines, you want to make full use of what you spent your hard earned $ on - because it equates to more HP. If you want to make full use of that big $ ignition system you bought, you should be using all of it. We do that with every other component in the engine. If you are concerned about putting undo load on stuff or breaking stuff, you are in the wrong hobby. The scenario I previously gave about the smog era and improved ignition systems is an example of why a higher voltage, larger spark, and longer ( in duration ) spark is better. Has nothing to do with the quality of the fuel, but with the extremely lean ratios coupled with the infusion of exhaust gas ( EGR) to control NOX - to meet emissions. Conventional ignition systems of the day couldn't lite it. Welcome to HEI! Higher voltage, longer duration (MSD )and bigger plug gaps COULD light it. No matter what causes a poor environment for lighting the fuel in your combustion chamber ( lean, rich, high CR, boost, N20, etc), higher voltage, larger spark, longer duration is always the better way to go. Hence my comment to the OP, " you want to run the largest plug gap you can and still be able to light the plugs".

What does it take for you... I said I tried larger
gaps and seen ZERO change in ET or MPH... that was
from a .025 to .060.. in .005 increments... you can
run what ever floats your boat.. I use .035 now and
have for a long time now... my 7AL makes the 55K+
and I have seen it on a scope also
EDIT
Maybe you play with emissions... I dont on any of
my cars that I race

std stroke 446 with MSD 7 with a 16 volt battery 11.6 to 1, ran .035 liked it... tried .040 didn't like it so much but still ran hard, was told I should run .018 didn't like that at all so went back to .035, next I will test ,032 and see.

Wow.......

Let me just put this thread this way, just because your AF meter reads 12:1 doesn't mean that that ratio is the same throughout the entire combustion chamber. There will always be some leaner areas and some richer areas. If a larger spark and a smaller spark would both light the mix, which one do you think would do a better job of lighting ALL the mix? If you don't run the largest gap your ignition system can support with your particular engine application, you will be leaving some HP on the table. I'm done!

Mag gap isn't relevant, they produce very little voltage at cranking speed and wouldn't start without a small gap.

Your argument is STILL based on "because I say so". You have given no facts, only your opinion and related things about new cars, which has zero bearing on the subject. While there have been several that claimed smaller gaps gave greater power......your reply is "you had something else wrong". Again, that's a "because I say so" argument.

And earlier, when I asked you to elaborate, I didn't see the post where somebody had already asked you to do the same and your answer to them. It didn't come up on my screen for whatever reason. Guess I hadn't refreshed the browser. But anyway, you got defensive and decided to be a smart azz about it, when I just wanted to see your reasoning.

With a magneto and 50+ pounds of boost our gap is .014.

You started the smart azz crap Mr "oldwives tale". That comment was unnecessary and to quote YOU, " has zero bearing on the subject". I can give you as many claims for a wider gap as you can for a smaller gap. Here are two from a very reputable source ( which I will not divulge - including his age). "Insufficient gap can cause pre-ignition, detonation, and engine damage." " A larger spark to the A/F mixture maximizes burn efficiency". Claims and opinions are just that. So are facts for that matter. We all have opinions, and YOU probably have one of the largest OPINIONS on this web sight!!

This conversation reminds me of the old time spark plug cleaner/tester machines. You could clean the plug and then test it by screwing it into a sealed chamber in the machine, hooking an ignition lead to it, and pressing a button to make the plug fire. Look in the window and turn up the air pressure until it blew the spark out like blowing out a candle. Higher pressure = harder to get it to fire. Only 2 options, turn up the voltage or tighten the gap.

My gaps have tightened up quite a bit over the years.

I run the maximium gap I can that won't miss at peak RPM at WOT
This is the United Staes of America and you have the rights and priveledges to run what you want

After doing some more reading on the web, plus im hitting it with a 100 shot of nitrous,Im going to stick with .035. Thanks everyone


BTW this car is race only, never to see the street

I would start at .035 and close it up until it slows down. Also you SHOULD be using a racing plug, and they have cut back ground wires, which effectively opens the gap without increasing it.

That's exactly what I said in an earlier post on this thread. " If you can lightem, the wider the better".

Today I happened to pick up an old (OLD from the early 90's) magazine. Can't even remember what is was. I think maybe Popular Hotrodding, but not sure. They had a story on different "performance tips". One was spark plug gaps. It said for Supercharged/Nitrous engines like .020 - .022 and high compression engines .022 - .025. They didn't mention MSD or anything like that so I'm figuring they were using old style electronic or points. Remember this was the early 90's.

I can see their point of close gaps. "Quicker" spark and probably a "shorter/fatter" spark.

That's just my take on their theory. Is it right or wrong? ?????

Here is the thing about modern ignition systems. It puts out, what it puts out. You can make spark jump a mile, but it will be no hotter and no more intense. It just is what it is. And as already covered, the MSD is a multi(ple) spark discharge, meaning you get more than a single pulse of spark per event. You get multiple sparks. An MSD is also a CD ignition, meaning capacitive discharge, which produces a VERY high spark voltage, by charging the coil quickly with high power. A digital 7 for example, produces 190 millijoules per spark. CD ignitions, while hot, produce a very short burst and that is why the Multi spark concept was designed. If the arc time is short, just make a lot of them.

Factory cars on the other hand, have "induction" type ignition systems and always have, which means the fire is relative to the saturation time on the coils and is a single spark. That's why old schools coils are so big. More windings, more saturation, more energy. The problem with induction ignition, is dwell time to charge the coil. Whats good at low speed, is not good at high speed, so it's a compromise at best and can't be adjusted. If you remember points days, the number was generally 32* of dwell. That's a compromise, because at low speed 15* would be better and at high speed 60* would be, but we couldn't do that. This is where HEI came in. It is basically a little computer that adjusts dwell time in relation to rpm, but it had a small range of about 15-40*. But ALL inductive systems still suffer from a thing called "roll off". Which means as rpm increases the saturation time on the coil gets too short to be efficient and spark energy gets weak.

Now that ignition basics and how it works are covered......do we want to talk about coils. Because the box is the box and makes the power it makes. It's ONE and ONLY job is to charge the coil. The COIL is what delivers the energy to the dist and or plugs and they come in various styles. Some have very quick peak energy and some have sustained energy. So as with any other part of a car, the TOTAL SYSTEM is what matters, not one individual component. Right box, wrong coil..the system won't work well.

I talked with an MSD design engineer last year when I bought my 7AL-3 unit, and he told me that the MSD spark duration was 20 degrees up to 3000 rpm. He also told me that for street cars to run a gap of .040, and for higher rpm strip cars, the gap was determined by the coil selection from MSD.

He also told me that as the rpm increases the MSD spark duration gets much shorter as per the design of the unit.

So, my understanding it was .035 -.040 depending on RPM and the MSD coil selection.

I have a Vertex Magneto on my Ford 427 engine, and the spark plug gap is .018, and the points are set at .014 - .016 as per the manual. I also run solid copper/steel plug wires and NGK plugs that have NO resistors, and fine wire electrodes.

Again, what I have been told by MSD and Pat Mason Racing Ignitions for the Magneto.

BR, Mark