Dial in question
 

What is the difference between water grains and vapor pressure?

How would you use that measurement to predict +/- when dialing a small block stocker?

Any insights would be accepted.

Re: Dial in question
 

GRAINS OF WATER-is a measurement that has to do with how much oxygen has been displaced in a cubic foot of air in relation to the maximum amount of oxygen that is normally present in that same cubic foot--a normal cubic foot of air has about 8000 grains of water & 21% of oxygen so if the amount of grains decreases to say 7500 grains then you will have a larger percentage of oxygen available to the engine and the result is more power --- more grains of water means less oxygen available and results in a corresponding decrease in power.
WATER VAPOR PRESSURE- has to do with humidity and barometric pressure---generally when you have high humidty you will have a lower barometric pressure reading but part of this is related to ambient air pressure too--- so if you have a warm humid day you will have a lower barometric pressure reading which generally results in decreased performance--- you can also have a high humidty cooler temperature situation but have an increase in barometric pressure and still have a lower engine performance. That's because of the absence of available oxygen due to the increased grains of water in the air
Basically Grains has to do with the percentage of water in the air and pressure is the weight of the water in the air

Hope this helps--- google it and read up on it you will learn quite a bit about how & why Grains affects engine performance --also look at Vapor see what it has to say

Re: Dial in question
 

Got that Joe.

Re: Dial in question
 

Lee, clear as mud, but i do understand the concept.

Now I want to figure how to quantify it.

Can anyone give me their formula for grains or vapor pressure? Is there one?

Which one is more accurate as a mesurement of HP?

Re: Dial in question
 

Once you get a grasp on it it is really not that hard to figure what your performance should be with a given set of values. This is why it is so important to keep records on past performances--FED 387

Re: Dial in question
 

Most people I know use correction factor or DA. My car doesn't change much based on vapor pressure, nor water grains. I have a friend that gets hung up on the barometer. I can dial mine off the trailer within 01 (1/8th mile) just looking at the correction factor (except in Topeka LOL).
However, I have thought the same questions that you are asking...