Originally posted by Pal:
I'm running a 68 250, bored .030 over. The head requires 5/8" nut plugs (narrow passage on the head). The distributer is from a 75, electronic ignition, separated coil. Now, with all that in mind.
What plugs and gap should I be using? I found plugs to fit, but gapped them to the 68 standard (.035). Should I be gapping these to .045 (or higher?) because of the E ignition? Currently, the truck performs ok (power), but gets poor mileage (about 12), and diesels at shut off. Thanks.
I've found that there are as many opinions on the correct gap for HEIs as there are guys runnin 'em. Supposedly, when they first came out, GM recommended a gap of .080. That seems a little wide to me....and it must have to GM too, because now most of the time the parts computers show a recommended HEI gap of .035 to .045. I've tried running both or either and I can't tell any difference at all between the two.
As far as the dieseling, 90 percent of the time I've found that it's because the idle is set too high. And many times it's because the builder/wrench can't get it to idle smoothly at anything less than 900-1000 rpm. In most of those cases, the culprit turns out to be a intake vacuum leak.
Just my experience.
