altitude racing anomiles

altitude racing anomalies

So was racing at the nats and LODRS back to back races at Bristol Dragway. Class Top Dragster. Have raced there several times with some with a win and a couple r/u. At the Nats made very consistent runs and had a good DA/ET ratio which oddly was double what I usually find at basically all other tracks but it proved to be spot on for every run, driver just needed to wake up...

For the LODRS seemed to go back to my normal ratio, only explanation was different track prep??

During Q2 on friday I made my quickest pass 6.685 with 8 mph tailwind. DA was 3700. Q1 had different trans and Q3 was .03 slower than should have been for everyone so throw that one out.

Race day morning DA is 3000 no wind so trusted DA/ET ratio and predicts predicts 6.61. Car runs 6.54! (predicted. killed 12MPH and still broke out by .02) 5 MPH faster at the 1/8th. Same lane.

Kestrel Weather data for both runs
DT WD T WC RH WG HI DP WB AP BP AL DA AD RAD
s mph °F °F % gpp °F °F °F inHg inHg ft ft lb/f? %
6/20/2014 14:30 0 1.2 87.1 87.1 55.7 113.6 93.2 69.4 74.3 28.48 28.48 1356 3776 0.068 89.4
6/21/2014 10:30 0 3 73.9 73.9 82.3 109 75.9 68.1 69.8 28.42 28.42 1410 3011 0.07 91.4

Of course every incremental was a lot faster than Q2.

Track notes
Q2 temp 113
R1 temp 90. During burnout track very slick never offered to hook up all the way past 60'

Question is:

What could have made this dramatic increase in HP? Is this something that is unique to high altitude racing? The reason I ask is because I experienced something kind of similar at bristol several years ago.

A friend mentioned oxygen content increase because no wind??

Car setup is
RED with 526 Chevy 1471 littlefield HHR bird catcher 25# boost, powerglide trans

Thanks

 

Reply

I keep same pill on all weekend as I can change dial for weather changes. The weather data got jacked up above sorry. The water grains for slower run 113. Faster run 109. Humidity was 56 for slower run and 82 for faster one. Slower run ds curve almost a perfect gradual climb. Faster run has a pretty significant hump indicating a some spin then it grabbed and pulled back down. However 60' was 1.02 versus 1.00 for faster run.

Thanks

 

long winded

sorry mike my post was so long winded, but weather station data from kestrel posted above (sorry format got jumbled because of space I guess).

But what from that data would indicate a .10 ET increase?

The DA difference would only indicate a .04 ET increase based on established DA/ET ratio that has been databased over many years of this same combination and proven itself at other tracks and even this track the week before at the nats.

thanks for your time.

 

good info

good tips, didn't think about not being a linear relationship, will look into that further.

thanks

 

left foot

Will, thanks but not planning on getting that technical because my left foot still works (even though it is wooden!) but in this case where it picked up over a .10 (water grains within 3%) just had me scratching my head. I can drive a hun or 2 but not 11 hun I guess.

But I will give more thought to keeping same pill in for the weekend, my train of thought was that I needed to keep as many variables the same and use a DA/ET change ratio to determine how it was going to run (carry over from carb days). Mike has thrown a wrench into that philosophy. I have been decently successful doing this over the past 5 years but I am always looking to design a better "wally" trap.

BTW, thanks for the timing map advise it helped.

 

vapor pressure

educate me on actual vapor press and saturated vapor pressure, or does water grains take place of this?

thanks

 

Good one

Will; thanks for the laugh ! I can visualize that conversation perfectly......Jay being Jay...... and Norm's beanie cap propeller going supersonic !

Also, while I'm here....it's not just the jet, don't ever forget the effects of timing with severe altitude change (i.e. Denver) the fire WILL be in the pipes, meaning retarded and false thermocouple readings !


Bob Meyer
Meyer Race Cars / San Diego
2014 Our 49th Anniversary

 

Does Jetsize account for extreme changes in humidity and accurately adjust its main pill recommendation?

I've been told that GoW and Vp are telling you the same thing just in different units of measure.

GoW and dyno scenario.
So this spring we were running a well proven engine on the dyno and I am extremely confident in setting its main pill for the density altitude, in average humidity. It was raining outside and was fairly cool, about 60-65°. GoW was about 45 and I had to go about .015" larger in the main pill to color the plugs to the point I would have had for that DA in normal humidity.

I understand that air can't hold as much water when its cooler, but I don't understand;
-how there could only be 45 GoW in the air whens its raining outside?
-why with that low of GoW did it effect my tuneup that much?
-it appeared to me that I need to adjust for the humidity based on what the temp is, but than that is called relative humidity!!!

 

I just got the page over the PA here at Woodburn. Let's start with some basics.

Relative Humidity is complicated. Grains per pound of air is simple.

There are 7000 grains in a pound of anything. So if the GPP is 70, there are 70 grains of water in every 7000 grains of air. So that's exactly 1.0 percent.

But the water (at higher GPP) starts to affect the combustion process, cooling the gases as the water vaporizes. Some tuners advance the timing at higher water grains, some people add compression with thinner gaskets.

Casey wants to bracket race and not mess around with these kinds of changes. I get that. Oh . . . they just called us to the lanes!

Patrick Hale