Another Gnarly MSD Distributor Cap

[Excaliber]

One advantage is the multiple spark discharge that occurs in the lower rpm ranges. This keeps the plugs burning extra clean and assures a more complete combustion than a single spark system, like the dura spark. The downside of the extra clean plugs is it makes it all but impossible to "read" them, if you were so inclined to do so. Most folks either don't know how or don't bother.

[Bobcat]

Interesting what Barry said about plug gaps . I was talking to Rob Pond the other day and he said he preferred .035 gap and no larger than .040 ( for many reasons ) .... every engine builder has his preferences and valid reasons to back them up . Plugs were AR 3923 .
Ernie ... correct , the new MSD ignition systems make it more difficult to read a plug , but where you really must read a plug for WOT mixture is at the base of the insulator , and that is shielded so you can get a good reading of the fuel ring , which will be a ring about 1/16" wide and a light gray if WOT mixture is correct . It takes at least one 1/4 mile run at full throttle and a clean engine cut to be color the insulator .... and a GOOD plug reading light . You can be dead on for WOT and still have a white insulator . Mid range , as you said is more difficult .

[undy]

I'm running a Standard Ignition "Blue Streak" cap 'n rotor on my Pro Billet and have had it on for 9,000 miles (3 years) and it still works fine. It's for a "points" SBC. Dump the MSD caps.

[patrickt]

My engine builder recommended a gap of .040 and the Champion RC9YC5 plugs, which is what I use with my full MSD setup and my Edelbrock heads. Edelbrock recommended one notch warmer, the RC12YC5 plugs in fact. MSD recommends that you go colder than what the head manufacturers recommend, so I guess they would want to see the RC9YC5 plugs. They also recommend a little bit wider gap than .040 with a 10.6 to 1 compression ratio, like I have. I've always had good luck with Champions, but WTF, there's no shortage of guys that say they're crap either.