gap for plugs - MSD box & dist.

The statement in post #2 is completely wrong, there is NEW technology. The writing mannerisms remind me of someone that has been banned from this site at least twice before....


Platinum, Iridium are just two of the new boys on the block.
The plug you are using is a hott-ish plug which is a good idea. NGK equivalent is a 5.

If you go to a Plat or Irid plug, you get two major benefits: long term reliability & higher spark energy which allows you to run a bigger gap. The smaller electrodes of P & I plugs require less firing voltage, which means they can run bigger gaps. The benefit of a bigger gap, exposing more spark to the mixture should be obvious. With a canister coil, I would use 0.055" gap, 0.060" gap with a an E core ign coil. MSD actually recommends 0.060" gaps up to 10.5:1 CR with the 6A box, & that is with stock coils & stock spark plugs.
Stock plugs on a 68-71 340, 10.5 compression is a Champion N9Y. Add a C for the newer plugs (copper). With your 9.5 compression you should be correct. A platinum plug would be a step up as you state, in Quilty. I use the Axcell distributor, duel point with the added Super Coil and the stock N9YC plugs, everything works fine. In believe, "if it is not broke, don't fix it". BTW, this motor is in my van, not car. Car is all stock.