Slant 6 Turbo 68Dart Project

It is a real thing, depending on on how many atmospheres are in the cylinder - it increases the gap by that many times. So ~14psi for one atmosphere, 150lbs of compression (kinda) would be 10.7 something. Let's say it's 10 times. SO a gap of .040 @ 10 atmospheres would be 400 thousandths, which is kinda close to 3/8 of an inch. That requires a bit of voltage to cross that gap. I'm not sure how much though - that part of the math I am unfamiliar with.

For every .125 you are talking an 1/8 of an inch though.

@.035 the spark would jump ".350" and at .028 it's .280 (in a perfect world).

Then you add pressure - jump distance increases.

So if a slant is meant to run a .045 and there is "150psi" of compression, and no boost, then the gap jump is .450 if my math is right (which it could not be, and air is not necessarily perfect, and you may not have 150psi in a cylinder, but for the example you do)...

So @20psi of boost, I'd think you want to reduce the gap by about 1.3 atmospheres . So you have 170psi compression now -

170 /14 = 12.14.
150/14 = 10.71

At 170psi the gap is 12.14 times the amount it is. So a .045 gap is really .546

At .035 it is .425 which is slightly less than the gap at .045 Naturally aspirated.

If you were able to get a good median estimate of all the cylinders in your car's compression and found the actual conversion table - and measured by an actual atmosphere - AND found the exact awesome gap an N/A slant is meant to run at - you may be able to figure out the EXACT gap to reach the same specs at 20psi.