water grans

How important is water grain's to your tune-up. I haven't payed that much attention to it in the past but maybe i should. We raced over the weekend and and ran the same tune-up Sunday morning as we had Saturday evening with similar weather readings except air temp Sunday morning was up 3 degrees and density gauge was up 1 point. The only thing i didn't check sat or sun was water grans. The car was 11 hundredths quicker on sunday. Car is a blown alcohol altered running a 7.60 index class.

 

We run an 8.0 boat. Blown, alcohol. For us water grains are important....well... bear with me.
It seems as the 100 grains is the magic point where it kills et. Back here humidity is common as is heat. If we are in the 75 to 90 range, no issues. Around 95 it starts to kill et a little. After 105, it kills et a bunch. Like from 85 to 110 would kill .1 et easily. Pay attention to it. It will put ahead of the competition.
I hear the gas guys aren't affected as much as us alky guys.
Oh, we have a mild piece. It takes 13# boost to run the 8.0 et. We step up to 20# to run a 6.0 et @ 1000', so not a huge power level involved here.
Wags
Oh, once it goes over 120 to 130, it does not effect et as much as 95 to 105. Hope that helps.

 

Wags,
Just out of curiosity, where are you taking your readings, at the pit or at water level? Back when I was running boats, (shortly after the Stone Age) I would send the son of one of my crew guys down to the water with a density guage (yes I know....archaic, but thats all we had then...) and get a reading. Some places we ran the pit area could be as much as 75-100 feet higher than water level and the readings could change as much as two tick marks on the guage. Of course water grains was a term seldom if ever heard back then, and I've often wondered with todays tech instruments what kind of reading you would get at water level as opposed to being a little higher up on the bank.

 

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I'm surprised to hear that you wouldn't suggest to compensate with fuel mixture since changing compression and boost is a lengthy ordeal. Please explain

 

Thanks for the input on this. It looks like i need to start adding water grans info into my log book and keep better track of how it affects our car. Nitrous is not allowed in the class and changing static compression is out of the question. Right now i am tuning 40% blower,50% timing and 10% jet so i can always adjust boost to compensate. Some testing will probably be in order to come up with a boost to water grans ratio. I also need to check with Kestril to see if water grans are taken in account when checking density altitude on the weather station. BTW Wags, i still rely on my trusty air density gauge quite a bit. It was up 1 point and i should have tuned for it. Thanks,Bob.

 

Water grains slows down the flame travel in the chamber. (As water does not burn, etc.)
Back in the hay-day Warren always told me to up the timing to get the flame started sooner as the water grains went up.
I have always run it that way with good results, but different engines have liked different changes in increasing timing. (So you have gotta play with that to find the happy medium.)

 

Our combination responds well to timing changes so that's an option also. We'll have to play with it a bit and see what works the best. I would be interested to no how jetting relates to this also. We are usually pretty fat on the jet, that's why i don't tune much with it.

 

Wannabe, you hit the nail on the head...you put more leed in it after I watch my wet bulb and dry bulb and do the calculating if it is over 100 I add more timming 2 to 3 deg. Dave

 

very true mike, what I will do is add 1 maybe 2 degs only.Dave

 

What do you use to measure water grans or how do you calculate it out.

 

i bought this kit it comes in a black case if you want i will send you the name of it tomorrow.Dave

 

yes if you could thank you.

 

This is what i have but haven't been keeping track of the water grain's, but that is going to change.http://www.nkhome.com/pdfs/kestrel-library/racing_brochure.pdf

 

Water grains free source

For many of the land tracks in the US & Canada, check airdensityonline.com

Once a track is selected, air density, density altitude, grains of water, and corrected & uncorrected barometer are provided for that track. A forecast prompt is provided to get air density, denstiy altitude, and grains of water forecasted out a couple days. For example, here ia a link to Indy: http://www.airdensityonline.com/trackForecast.php?trackname=OReilly%20Raceway%20Park&bar=28.952891051151

All data is from the nearest National Weather Service Center to that race location.

If boat racers are interested in water grains for boat racing locations, email a request to the web site.

In the tracks local to us, we have dry air in the day time and humid air in the evening. I have seen a water grains change equivalent to a half inch of mercury on the air pressure scale. That is significant.

On page 117 of our book, 5000 Horsepower On Methanol, an example of 107 grains of water is illustrated for a typical race engine. It is over one pint of water per minute going through the engine example.

Bob Szabo
bob@racecarbook.com
www.racecarbook.com
www.airdensityonline.com

 

We check it at water level, next to the water (cause I can't get the crew chief to swim out to the track) ROFL
Wags

 

I use the Computech Race Air Pro. The pro has somee engine calculations that are handy for me. I had the earlier Computech deal that you had to plug some numbers into their calculator. The racer Air Pro is very repeatable. My this I mean crew chief can check air, look in the log book, and dial an 8.0? in almost every pass.
It does all the calculations for you and displays them in a scroll screen. Temp, humidity, baro pressure, adr, da, water grains, wet bulb, dr bulb, etc.....
It has a build in fan, several jet, cr, et prediction programs built in.
http://computechracing.com/index.php?main_page=product_info&cPath=1&products_id=29

Oh, the comutech guys turned me on to water grains a few years ago. For us bracket guys, it helps greatly.
Good luck.
Wags