Dyno Readings ?

[MCMIKE]

What does the VAPOR PRESSURE refer to on the dyno sheets,and how will that affect actual trackside tuning.I had one pull with .15 and the other with .48, pulls were made on seperate days.

[Chris Uratchko]

It's a calculation of moisture in the air. You tune your ignition timing to this measurement. Higher the VP, more timing requirements.

Another tool for timing is Grains of Water, which might be a little more accurate, but both are good indicators.

And all of it is subjective for every engine. Some engines want X amount of timing for every point in VP, others are not as sensitive.... so there is no real good rule of thumb, at least in my opinion... I used to think .1 of VP was about .5 degree of timing but.... again, subjective and relative to the engine.