The manual for my 85 L98 calls for a .035 gap on stock ignition. What should it be after adding the MSD coil and 8.5 wires. The plugs i took out were scorched around the ceramic. :confused:

 

You can take them out to .40 but it's not necessary. The farther you put them out, the longer the spark takes to get there, hence your hurting more than the possible gains of a larger gap. There is a happy medium in there somewhere, usually around .35-.45 where the spark is just right.

 

I've read a few interesting books on this spark plug gap subject and they all said basically the same thing:

No power increase can be realized unless the spark plug gap is increased over the stock setting. As an example, one of Jacobs' systems requires a .060 plug gap.

The problem with wider gaps is, like water, spark will always try to take the path of least resistance. The spark will always try to find a way to ground that is easier to jump than to jump the wider spark plug gap.

If it finds such a path, it'll jump there, rather than the wider gap. So you can end up with spark jumping to the exhaust, valve covers, from one wire to another, inside the distributor cap, etc., instead of jumping the gap at the plug.

When running higher output ignition setups and wider gaps, you'll always see cautions that proper plug wire separation/insulation etc. is essential to prevent the spark from jumping to ground at places other that the plug gap.

There are a lot of ways to address this problem, with sleeves over the plug wires, better plug wires, wire looms, distributor cap made out of better material, etc.

The problem may not show up right away either. At first all may seem well with running the wider gap, but after a while you may experience an occasional miss. Over time you may end up seeing all kinds of fireworks under the hood when the engine is at idle in a darkened garage.

So, you'll increase power by running a wider gap (assuming your ignition system is up to the task), but care must be taken to make sure all the components are top shelf.

Just my thoughts.

Jake

 

You'll make more power with a wider plug gap, period. The question then becomes, what can your ignition system fire reliably and how often do you change your plugs, etc.

I have an MSD digital 6 with MSD wires and an MSD coil. Factory spec on the LT1 I believe is .05, I run .06 without any problems. Just remember that as the plugs wear the gap will increase even further, and as stated above, misfires may start occuring. It's very easy to check / regap / or change my plugs. As such I run the bigger gap and just keep a close eye on them. If you never want to touch your plugs again just install a set of platinum plugs at the specified gap and forget it for another 100k miles.

The factory plug gap is a compromise. The initial plug gap has to be small enough so as to allow the plugs to wear somewhat and still function properly.

 

Thanks. Even after I gapped a new set of plugs to .060 I pulled them today and they are still toasted. :cheers:

 

Describe in detail what you're seeing on the plugs.

Jake

 

well the ceramic is still a nice brown color except there is a discoloration that looks seared and it has a cone shape to the mark tapering to the top of the plug. its dark brown

 

Jake, you are spot on about a wider gap causing the entire system to seek the shortest path to ground. One other thing to possibly mention is when no other path exists, everything in the system is really being taxed to jump the wider gap on the plug and eventually a shorter path or even a misfire will ultimately occur, hence your fireworks under the hood. One last note, the thermodynamic efficiency of the fuel burn is not so much the size of the ignition source as it is "when and how long" the ignition source is applied as well as the amount of turbulent flow in the air/fuel ratio. Since we really don't have much control over the turbulent flow once the engine is built, we must concentrate on proper timing and the curve in which it changes throughout the RPM range. What you are looking for is a fast burn. Normal gaps, say 0.35 - 0.40 are generally a good starting point but if you want to optimize the burn, there isn't much that beats a multiple spark with a normal gap.

My two cents.
Finally it's Ed

 

I've read that the benefit of the larger gap is to achieve a more complete charge burn.

 

And that's the fun of it, there are tons of conflicting ideas on just about everything, but the real funny part is if you contact Autolite, Champion, or even MSD, all you'll get back is, "please refer to your manufacturer's recommendation on plug gap."
A good example of electricity taking the shortest and easiest path to ground is the new three electrode plugs where only one of the electrodes actually spark, not all three.
I do still stand by my understanding that the larger the gap beyond normal range, i.e.(0.030 - 0.045), the more likely there will be a misfire as components degrade.
Ed

 

 

Maybe so, but man, this was hilarious!!.....

 

That's why Kman has been off this forum for 7 years and is driving a Yugo.

 

Actually, Jake passed away quite a few years ago.. He was a good guy...WW

 

I've read tons of his posts and always been amazed at his knowledge.

 

x2
keep the gap at .035