MSD6/258 Spark Plug Recommendation

[84_CJ7]

Got the MSD6 successfully installed and working - but still waiting on a carb swap to complete my tinkering.

I read somewhere that the MSD box likes cooler plugs. Is this right?

I'll continue to play with the gap - started at .050 - but has anyone found a happy medium? Don't want to put too much strain on the coil.

The only thing I ran in to that surprised me was the amount of ignition timing shift from the HEI module. I rotated my distributor almost to the point of no more available twist due to the vacuum canister hitting the block. I could probably pull and rotate the starting point of the distributor and get two more pounds of manifold vacuum.

I set the timing with the MSD at 8 BTC @ 1600rpm for a starting point.

Any thoughts or recommendations would be appreciated.

[Jim_Lou]

The only factor relating plug heat range and ignition module that I can think of is that a more powerful spark with a faster rise time can fire a fouled plug better than a weaker, slower ignition system. But there's no reason to ask for the plugs to be fouled just to prove the point. Plugs go with the engine, not the spark box.

[LEVE]

You're starting point for the distributor is correct. I wouldn't move it more unless you see a need. Often that need points to another problem that crops up. Then it's best to discover the reason for the change, root out the problem and solve it.

As for the gap, the MSD is just that... Multiple Spark Discharg over the dwell time. The spark plug is a pretty dumb device. It just sits there and endures a lot of heat and pressure and lets the spark jump from the electrode to ground. In your case, multiple times when a regular ignition system would only spark once. The gap should be about .050" to .055".

The biggest thing is that you don't want to create a hot spot. This occurs when you use the wrong plug. The hot spot can occur on the surface of a piston. Then the piston will heat up and can become so hot a hole will actually melt through the top of the pistion. So, use the stock plug for the engine and increase the gap.

If you're really wanting to fiddle a little try getting some index washers for the plugs. That will orient the electrode toward the intake valve. It squeezed a little more power out of the engine. Not a whole lot.. but if you like to fiddle, fiddle to your heart's content.

[84_CJ7]

Thanks. Good to know I was on the right track. Right now I'm going to leave well enough alone.

My replacement carb (2150) came in today - hopefully I can get it mounted this evening. Naturally I have to make another throttle bracket to accommodate the difference in these two carbs. The factory bracket I am using was just too good to be true.