New to me MSD 6A box. What is realistic spark plug gap?

i have around 9.8- 10.00 compression by the way.

 

Thanks for the heads-up about platinum. I didn't know that.

So, now it is sounding like 55-60? I will be nearly DOUBLING my gap this afternoon...

 

GAP is relative to Compression Ratio

The basic rule is that as compression ratio increases then spark plug gap decreases.

This means if your following the factory specs for gap on a stock 302 with 8:1 compression then your probably throwing away some of your ignition's true ability. Remember that facotry spec's are based on a 15,000 volt coil. With MSD and a good coil you should be putting out no less than 40,000 volts.

 

I swapped coils right after I got this car. It has the Accel SuperStock coil. Yes, I know, not the best, but is it even decent?

If not, I will have to look into a better one.

 

I always run the plug gap as small as I can keep the engine idling smoothly.
The smaller gap allows the coil to discharge with a lower voltage and higher amperage.
The higher amperage is what ignites the fuel. Higher voltage than what is required to fire the plugs causes wear in the coil, the plug wires and means you have to change plugs more often.
Under power, when the pressures rise, the voltage will go up but not enough to cause the ozone damage to the wires and coil. (corona discharge)

Run what works for you - each car is different - each engine is tuned differently so what works for me might not work for you. Experiment with your rig and your tune to find out what works best on your application. Never tune yours to the same specs as someone else's just because it works for them. There is probably something that will work better for your application.

 

The pertronix ignitor is the point eliminator kit right? Why run it at all? The points will work with the MSD6 and last forever.
I ran .055 when I was running MSD ignition
clint

 

Got rid of the points years ago. Pertronix starts right up and has no wearing parts. So snap it in and forget about it.

 

I was wondering if anyone knows whether you can also advance the timing as you increase the gap of the plugs? I remember reading about that. Well actually, I remember doing that to the 351 I have in my bronco and it worked OK but I'm not sure if that's appropriate.

 

mo, on the fuel injected fords you could advance the timing from the factory seting of 10 degrees up to 14 degrees if you ran premium fuel. the msd boxes allow your spark to be more powerfull to over come the elivated cylinder pressure caused by running a higher comperssion ration, adding nitruous or, boosting a motor.

 

Thats exactly why you can run more gap when using MSD. MSD increases both the voltage and amps. Running the smallest gap possible just means you might as well throw away the MSD box and run off points and a coil. You mentioned your running the smallest gap possible because of idle issues, then you probably have something else wrong with your car like A/F ratio or timing. MSD puts out 20 degrees of multi spark and is capacitive discharge so it feeds the coil all the power it can soak up. If your having problems with idle running .035 on a stock motor then I would look into other possible problems.

 

Well, I haven't driven it yet. And probably won't until Friday (rain forcast for today and tomorrow). But after putting all the plugs at .060 it started right up and idled fine.

I was very amazed that it would run. Having never used MSD and it is a hidden improvement (you cannot see the spark or the gapped plugs). I expected to hear a lot of spit and sputter when I tried to start it or not have it start at all, and was pleasantly surprised when it just lit right up!

Also, .060 is HUGE! In fact, one of the straps nearly broke off where it is welded to the plug. I could feel it get real easy to move, so I tossed it and put in a new one so I don't have to worry about it coming off and bouncing around a cylinder.

 

Want to see how strong an MSD is, grab a plug wire end and have someone hit the key for you.

 

A coil will only produce enough voltage to jump the gap - no matter what power system you have driving it. Running a small gap means you have more power reserve to fire the plugs under extreme conditions, it means that the wires will last longer and it means that you will be able to go longer between tune-ups.
I didn't say I had idle issues - I said that I run the smallest gap that will still allow the engine to idle smoothly - too small a gap won't fire the rarefied mixture at an idle - Big gaps will easily fire the idle mixture. Big gaps require higher voltages - especially under power where a smaller gap is better. My engine is tuned perfectly - for me. It idles at 550 rpm in drive, smooth as silk, 10 BTDC with a total advance of 34 at 2800 rpm. The carb only goes to a slightly rich mixture under very heavy acceleration. I get 20 -21 MPG and all the power one would expect from a factory stock 302 with 100000+ miles on it. I don't have problems with my engine or tune-up.

 

I'm not going to get into the gap argument, But from personal experience i have found, No matter what kind of box or coil. If you build enough cylinder pressure, The wider the gap the more chance of a misfire. I have had misfire problems on a few Blower, Nitrous fed cars. Reducing the gap below 40 thousandths has always cured the problem. I personally run 35-40 thousandths gap and have never had any misfire issue.

 

Paul - I am not getting your theory.

V = I x R and P= (V^2)/R

So you are saying you reduce the gap which reduces the voltage required to cause the arc/spark. I am thnking the gap reduction is a reduction in resistance in the circuit. So, if voltage is down across the gap, and resisance is down(again I assume this), it seems to me that electrical power at the gap is reduced. How can this be good for firing off the fuel?

My model is incomplete as I don't have the R reduction to V reduction ratio. Just trying to understand the theory.

Jamie