[2009Prius]

Originally Posted by thecheese429

I was wondering if anyone had done tests on this, then decided to do my own. I have a 4 banger, so changing gaps across the board is not time intensive at all.

I changed the gaps, and then checked the vacuum. Then I changed the gaps, and checked the vacuum again. Here's the data:

          Gap (inches)       Vacuum reading (In. Hg)
Test 1:    .025                       16
Test 2:    .040                       16.5
Test 3:    .045                       16.7
Test 4:    .050                       16.7
Test 5:    .060                       16.9
Test 6:    .080                       16.7

No, my gauge doesn't have decimals, but the needle moved so little between tests that I figured I should use decimals.

My question is how this relates to FE. Does higher vacuum mean higher efficiency?

Originally Posted by thecheese429

Yes, the vacuum was measured at idle. The spark advance, EGR, and even idle speed are computer controlled, so I believe that the spark did change stuff, and then the computer compensated for it.

For those who are wondering, I am running a .040" gap now

And what is the manufacture's gap spec for your car? Thanks!