Dial in question

Joe DeMarzo · 08-08-2014, 11:37 AM

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.

FED 387 · 08-08-2014, 12:54 PM

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

Lee Valentine · 08-08-2014, 02:42 PM

Got that Joe.

Joe DeMarzo · 08-08-2014, 03:18 PM

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?

FED 387 · 08-08-2014, 03:41 PM

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

cad · 08-09-2014, 07:18 AM

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...

08-08-2014, 11:37 AM	#1
Joe DeMarzo Senior Member Join Date: Oct 2002 Location: Mahopac, NY Posts: 666 Likes: 48 Liked 114 Times in 9 Posts	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. __________________ Joe DeMarzo 1317 STK

08-08-2014, 12:54 PM	#2
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,349 Likes: 329 Liked 280 Times in 150 Posts	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 Last edited by FED 387; 08-08-2014 at 01:31 PM. Reason: incorrect percentage posted should be 21 not 23

08-08-2014, 02:42 PM	#3
Lee Valentine Senior Member Join Date: May 2004 Location: Brookfield, CT Posts: 708 Likes: 13 Liked 322 Times in 68 Posts	Re: Dial in question Got that Joe. __________________ Lee Valentine 1661 STK

08-08-2014, 03:18 PM	#4
Joe DeMarzo Senior Member Join Date: Oct 2002 Location: Mahopac, NY Posts: 666 Likes: 48 Liked 114 Times in 9 Posts	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? __________________ Joe DeMarzo 1317 STK Last edited by Joe DeMarzo; 08-08-2014 at 03:19 PM. Reason: spelling

08-08-2014, 03:41 PM	#5
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,349 Likes: 329 Liked 280 Times in 150 Posts	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

08-09-2014, 07:18 AM	#6
cad Senior Member Join Date: Apr 2009 Location: Omaha, NE Posts: 673 Likes: 141 Liked 72 Times in 40 Posts	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...