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Density alt, vapor press, or water grains???????? #1060204
08/23/11 01:18 PM
08/23/11 01:18 PM
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Posts: 10,542
BROOK PARK, OH
WILD BILL Offline OP
Senior Member of the Junior Dragster Club
WILD BILL  Offline OP
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I've been wondering this for a while. I currently have a TAG weather station to gather the data. I'm watching Temp, RH, BP, \and DA for all 4 cars. 3 on alcohol and the 4th on pump gas.

All I've ever heard about in the past was DA this and DA that. Then, I read the instructions for the TAG and it says the Vapor Pressure reading would be for Alcohol motors. I've never heard of VP until this.

However, I keep hearing people referring to water grains and some say this is one of the most important things to watch when trying to dial a car on Alky.

SO, what should I be looking at to get the best chance of understanding how it affects the cars?

My Tag won't do WG's so is there a stand alone meter that will or should I just bite the bullet and get a Kestrel?

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060205
08/23/11 03:18 PM
08/23/11 03:18 PM
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Bend,OR USA
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Cab_Burge Offline
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Buy the Kestrel for the water grains and wind information, use the TAG for predicting with its information based on RH You will see the trend on the ET differences between the little cars on alcohol versus the big car on gas.Do you keep two different data input logs for the big car versus the JRs? If not, why not, for predicting


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060206
08/23/11 03:19 PM
08/23/11 03:19 PM
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NC
440Jim Offline
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Check the TAG instructions etc for more detail.

IMO,
water grains, <water> vapor pressure, etc. are all related measurements refering to the amount of water vapor in the air. And alcohol fuels are more sensitive to this than gas fuels. Relative humidity doesn't capture the entire picture, since it is a ratio of the maximum amount of water vapor possible at a given temperature to the actual amount of water vapor. So if the temperature drops and the total water gains or water vapor pressure stays the same, the relative humidity still goes up since colder air cannot hold as much water vapor.

I think your TAG has all the information needed (Temp, RH, Baro). With 3 of the 4, it can calculate the other and even density altitude; in this case it can calculate dew point, water grains, or vapor pressure. Again check the instructions, but I bet it just wants to know which prediction method to use based on the fuel. One is temperature/DA biased and the other is humidity biased.

When the barometric pressure is 29.92"Hg (for example), the amount of humidity (water vapor) in the air is part of that (partial pressure of water vapor). So it might be 29.21"Hg of air pressure and 0.71"Hg of water vapor pressure.

Re: Density alt, vapor press, or water grains???????? [Re: 440Jim] #1060207
08/23/11 03:38 PM
08/23/11 03:38 PM
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
WILD BILL Offline OP
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I do keep separate logs for each car although I have never entered any of the data into the dag. It is setup for each separate car and can record 4 separate log books.

I have the Tag Dyno Log installed on my lap top that I use for my runs and then the data recorder for the Jrs has software that you enter the run info into.

All these have an entry for DA yet none have anything for VP or WG's

I'm not sure at this point if I can go back and back enter all the runs and weather for each car into the TAG or if it has to be done at the time of the race.

If it has to be done at the time of the race that would be next to impossible given the pace that I have to keep to run my car and the 2 girls. Dad is pretty self sufficient and rarely needs my help but when something arises on that car I need to thrash there too.

In other words, I'm often just jotting down notes on the times slips and then inputting the data much later when I have time.

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060208
08/23/11 04:13 PM
08/23/11 04:13 PM
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Romeo MI
MR_P_BODY Offline
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Quote:

I do keep separate logs for each car although I have never entered any of the data into the dag. It is setup for each separate car and can record 4 separate log books.

I have the Tag Dyno Log installed on my lap top that I use for my runs and then the data recorder for the Jrs has software that you enter the run info into.

All these have an entry for DA yet none have anything for VP or WG's

I'm not sure at this point if I can go back and back enter all the runs and weather for each car into the TAG or if it has to be done at the time of the race.

If it has to be done at the time of the race that would be next to impossible given the pace that I have to keep to run my car and the 2 girls. Dad is pretty self sufficient and rarely needs my help but when something arises on that car I need to thrash there too.

In other words, I'm often just jotting down notes on the times slips and then inputting the data much later when I have time.





Bill the TAG doesnt have any place to enter a water
grains reading so you wont be able to... with the
data thats in the TAG I can run dead on IF you dont make
any changes to the car... if you do make a change
to ANYTHING on the car you need to start another data base
(or delete the old data base if you dont have a open
log in the unit)... it only has 4 data bases in it

Re: Density alt, vapor press, or water grains???????? [Re: MR_P_BODY] #1060209
08/23/11 08:12 PM
08/23/11 08:12 PM
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
WILD BILL Offline OP
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Mike, that's great to know once I get the car sorted out to where I'm done making changes.

However, would the VP be better to watch or the DA? I think I can set it up different for each car. IE VP for the alky cars and then DA for the gas car. Would this be best?

Should I not worry about water grains using the VP as it takes that into account?

Kinda lost on which one I should be concerned with.

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060210
08/23/11 09:04 PM
08/23/11 09:04 PM
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Tallmadge, Ohio
Butch Offline
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Wow now I have a headache

Butch



'74 Duster 440
'04 Hemi Quad Cab Ram
'06 Pacifica
'78 MGB
Re: Density alt, vapor press, or water grains???????? [Re: Butch] #1060211
08/23/11 09:13 PM
08/23/11 09:13 PM
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Posts: 644
Minnesota
Barnstorm Offline
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airdensityonline.com....takes my headache away.


The little old lady from Pasadena is back!
Re: Density alt, vapor press, or water grains???????? [Re: Barnstorm] #1060212
08/23/11 09:25 PM
08/23/11 09:25 PM
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
WILD BILL Offline OP
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Quote:

airdensityonline.com....takes my headache away.




Actually it just made the headache worse.

How accurate is their info?

And better yet, how does one use all this info?

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060213
08/23/11 09:40 PM
08/23/11 09:40 PM
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:

Quote:

airdensityonline.com....takes my headache away.




Actually it just made the headache worse.

How accurate is their info?

And better yet, how does one use all this info?





Bill, if you use the TAG as a ET predictor you have
to stay with the DA(thats part of its calculations)
I've never had any problem using it

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060214
08/23/11 09:47 PM
08/23/11 09:47 PM
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Posts: 7,348
Mt.Vernon ,Ohio
VernMotor Offline
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I found this to be interesting. grains of water sure don't follow DA. looks like if I was dial the car by grains of water it would be diffidence than DA

http://www.airdensityonline.com/trackFor...29.212410708722

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060215
08/23/11 09:50 PM
08/23/11 09:50 PM
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Belpre,Ohio
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Quote:

Mike, that's great to know once I get the car sorted out to where I'm done making changes.

However, would the VP be better to watch or the DA? I think I can set it up different for each car. IE VP for the alky cars and then DA for the gas car. Would this be best?

Should I not worry about water grains using the VP as it takes that into account?


Kinda lost on which one I should be concerned with.






I have a TAG too Bill. I have not used it to enter ANY data yet. I have not gotten enough runs that are consistent/comparable/identical/etc to actually compile any predictable results. I am like you, trying to get the car sorted out and running like it should. I will not try to use the TAG untill I KNOW I have the car reasonably dialed in and the car and I are both capable of producing near identical time runs. After I get that accomplished, I will try to enter some good/comparable runs for the TAG to predict. No offense intended, but, maybe you need more good/solid passes before you try to predict with your car..


If you like drag racing, support your local track.
Re: Density alt, vapor press, or water grains???????? [Re: CHAPPER] #1060216
08/23/11 10:15 PM
08/23/11 10:15 PM
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Bend,OR USA
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I bought a used Performaire Eclipse weather station and predictor last year,so I'm not sure if the current TAG units are like the Performaire or not I have kept race logs for a long time, I use to have and used one of the first generation weather stations and predictors, that one went bad when the memory battery ran out That company has gone out of business also My point is your TAG needs current weather infomation to predict accurately, like Mike has already said, it doesn't do any good to enter it at home after the race I erase all the runs in the unit I have if I make a mechanical change to the car like changing carbs,jets, tires or what ever I select the multiple runs for predicting and then use that information, along with a grain of salt, to decide what I'm going to dial Don't use last weeks information to dial in for todays races Good luck, don't get overwhelmed with to much information, remember the KISS principals and use that


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Density alt, vapor press, or water grains???????? [Re: Cab_Burge] #1060217
08/23/11 10:28 PM
08/23/11 10:28 PM
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
WILD BILL Offline OP
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WILD BILL  Offline OP
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BROOK PARK, OH
I was laying with the TAG while out at the trailer today and found that I can indeed manually input weather data to store a run.

So, if needed, I could go back and enter all my previous runs with the weather at that time into the TAG.

However, we're getting a little off topic. Using the TAG isn't the concern so much as HOW I should use it?

Will it give ET predictions more accurately for alcohol cars in VP mode?

When using a TAG reading VP is that basically the same or equal to reading and using water grains?

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060218
08/23/11 10:55 PM
08/23/11 10:55 PM
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Minnesota
Barnstorm Offline
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I don't know what your'e looking for..we use a 10 year old TAG unit that shows DA hum baro temp. A beer cruise with a smart phone at Brainerd showed it to be within a 120 DA feet of the average of 31 different devices. I can't tune 120 DA ft. Cheap and accurate. FYI


The little old lady from Pasadena is back!
Re: Density alt, vapor press, or water grains???????? [Re: Barnstorm] #1060219
08/23/11 11:12 PM
08/23/11 11:12 PM
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Romeo MI
MR_P_BODY Offline
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Quote:

I don't know what your'e looking for..we use a 10 year old TAG unit that shows DA hum baro temp. A beer cruise with a smart phone at Brainerd showed it to be within a 120 DA feet of the average of 31 different devices. I can't tune 120 DA ft. Cheap and accurate. FYI




It doesnt matter if its off by 120ft just as long as
its always off 120ft.... you use that one unit on your
car ONLY.....
Bill I cant say weather the VP is better or not...
I've always used the DA on my unit(its about 10 years
old now) but I've always been VERY HAPPY with it and
its predictions to what the car will run... mine is
within a few thousandths, which is closer than you
need to dial... if it says I should run a 9.009 I
put .01 on the window but if its a .005 I go with
.00... its that close and the car is also

Re: Density alt, vapor press, or water grains???????? [Re: MR_P_BODY] #1060220
08/24/11 10:40 AM
08/24/11 10:40 AM
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Dandridge TN
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Quote:

It doesnt matter if its off by 120ft just as long as
its always off 120ft.... you use that one unit on your
car ONLY.....
Bill I cant say weather the VP is better or not...
I've always used the DA on my unit(its about 10 years
old now) but I've always been VERY HAPPY with it and
its predictions to what the car will run... mine is
within a few thousandths, which is closer than you
need to dial... if it says I should run a 9.009 I
put .01 on the window but if its a .005 I go with
.00... its that close and the car is also





My ten year old TAG consistently has predicted ET’s with in .003. I have run gas, alky and E-85, in three different cars and it made no difference. All I did was dump the data and start with a fresh data base when switching fuel and or cars. The key is you need a few good runs in the data base to accurately predict. Also like Cab said if you make any changes to the car dump the data and start over.

Re: Density alt, vapor press, or water grains???????? [Re: Dabee] #1060221
08/24/11 10:56 AM
08/24/11 10:56 AM
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BROOK PARK, OH
WILD BILL Offline OP
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Why the hell has this turned into a thread about the TAG's ability to predict ET

All I wanted was to try and understand the differences and importance's of DA, Vapor Press and Water grains and weather watching either VP or water grains would give me a better understanding of how the current conditions will affect the run.

Re: Density alt, vapor press, or water grains???????? [Re: WILD BILL] #1060222
08/24/11 12:10 PM
08/24/11 12:10 PM
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Syracuse,NY
CompWedgeEngines Offline
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My

Lets remember what we are trying to accomplish here. We want our " weather station" to help measure the factors in the atmosphere that affect our engines performance. What are those primarily?
1) Available oxygen
2) Amount of water vapor

How do we increase horsepower? We increase th amount of available oxygen to burn, which in turn allows us to burn more fuel. More fuel, more power. More power, faster we go.

Density altitude was originally, ( and still) used in the aviation industry. You will notice that Kestrel units are sold in places like SPortys Pilot Shop and so forth. A simple device for pilots to use. Pilots needed to know this to determine the amount of thrust they need, or could develop to lift the aircraft.

Density altitude takes into account temperature, humidity,and pressure. Systems like I use assume a 20.9% available oxygen.( per volume) . I sue actual oxygen as measured by the air sampler.

Water vapor is a biggie in my opinion. It affects the rate of fuel burn, the dilution of the fuel ( water,and we all know engines dont like to burn water)and it actually changes the density of the air. If you know how this affects your engines performance, you'll be miles ahead.

Again, what do we want our wetaher station to tell us? Its the ability to accurately tell us what changes in the weather are occuring.

There are some rule of thumbs:

200' rise in DA = .01 slow down ( gas)
400' rise in DA = .01 slow down ( alky)

While these are only guidelines, you must know YOUR combination, and start watching trends. DONT just look at DA, it is not the end all do all to performance. Watch those grains of water, vapor pressure and so forth, then start determining how that is affecting your ET, ALONG WITH, what you are seeing on DA. DO NOT depend on someone elses weather station to predict your ET. Although they may show "X" amount of DA change and so forth, you must stay consistent and use your own data from your own machine.

If you took a 1 degree change in temperature, a .1 Hg change in pressure, and a 10% change in humidity,or even a .1% change in oxygen, any of those could equate to a 100' or better change in DA.

Also trhink of those nights when you are racing, and the car keeps pickup up, picking up, picking up, and your thin king " holy cow. we are going to run a new best " by the end of the night. Then the car just stops climbing, the 60" stops getting better, and you may even slow down. Heck, the air is cooler, " i can feel it"...cold air equals fast right? Ooops, better check the humidity and water vapor....We just started to try and burn dew.

Look at ALL the data, get a feel for what each change ( especially minor changes) is doing to your ET, and just keep using it, using it and logging data. Dont get hung up on DA alone.

If you ever notice, what do the Pro fuel teams watch the most? Grains of water. ( it does affect them heavily beacuse of the comression factors involved with blowers and such, but effects ALL engines none the less.)

Good luck Bill. I will call you about that Junior deal soon too.

Todd


RIP Monte Smith

Your work is a reflection of yourself, autograph it with quality.

WD for Diamond Pistons,Sidewinder cylinder heads, Wiseco, K1 rods and cranks,BAM lifters, Morel lifters, Molnar Technologies, Harland Sharp, Pro Gear, Cometic, King Engine Bearings and many others.
Re: Density alt, vapor press, or water grains???????? [Re: CompWedgeEngines] #1060223
08/24/11 12:30 PM
08/24/11 12:30 PM
Joined: Dec 2007
Posts: 10,542
BROOK PARK, OH
WILD BILL Offline OP
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WILD BILL  Offline OP
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BROOK PARK, OH
Thank you Todd.

So, I need to start watching WG's as well as everything else or will watching the normal BP and RH along with Vapor Press give me a good idea of how much water is in the air?

Does anyone make/offer a stand alone devise for measuring water grains?

For the record, I really need to get a handle on this mainly for the small cars. They run on an index and if they are gonna pick up do to the conditions I can't just dial them faster. I have to either add weight or tell my drivers that conditions are right for them to go faster so they know they may need to do something at the stripe.

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