Tech Information > Technical Discussion
The question...run in the cool dense morning air or less dense afternoon air??
Sumner:
--- Quote from: SPARKY on August 21, 2014, 02:38:29 PM ---Sum
Years ago I read that what made B'ville special --- its is real close to the cross over point of what you are trying to evaluate: HP vs Drag and that is was just about optimal---makes having a good intake system pretty important to be able to knock of about 1000' of DA
--- End quote ---
If you are gaining say 1 # of boost at 220 mph then you would still be back to the fact that that is less HP gain at the lower air density (high altitude) vs. more HP at a higher air density (lower altitude) and we are back to the fact of it is a 'wash' since as the HP goes up the drag increases to offset it. The car will run faster though but both at the lower or higher density altitude with the corresponding proper tune.
With a better intake we are making more HP and the car will run faster than say the 220 but the rules of air density going down (need less HP) and HP decreasing (due to increased altitude), with neither one having an advantage over the other still applies,
Sum
Milwaukee Midget:
Absolutely - It's less than 2% difference - the only consistent feature being the higher the adjusted altitude, the faster the car went.
It's a small sample, certainly not absolute, and there are variables not accounted for, but it does indicate a trend in this particular instance.
Here's how I broke it down last August . . .
--- Quote from: Milwaukee Midget on September 01, 2013, 01:28:32 PM ---Okay, let's go back to the run data -
Track orientation sw to ne
Date Time Temp Humidity BP D A Wind Wind Speed Mile 2 2 1/4 Mile 3 Note Air jet Timing
12-Aug 8:37 70.6 15 25.73 5863 ssw 1 102.464 Rookie 180 37
12-Aug 14:28 88.9 8 25.7 7008 s 4 109.781 114.844 115.886 180 37
12-Aug 17:08 89.8 7 25.66 7106 ese 9 111.12 115.185 116.698 180 37
12-Aug 18:42 90 9 25.65 7145 sse 10 112.234 117.155 118.069 180 37
13-Aug 9:25 71.9 31 25.78 5943 nnw 1 111.944 115.336 115.878 180 37
13-Aug 11:41 77.8 20 25.78 6279 ne 5 110.386 114.275 115.028 push start 180 37
13-Aug 15.29 88.4 9 25.73 6946 sse 5 113.319 116.444 117.293 175 37
13-Aug 17.57 91.5 6 25.68 7177 sse 11 113.586 117.161 118.257 175 37
14-Aug 11:07 79.2 22 25.77 6391 n 0 113.241 117.077 117.816 170 37
14-Aug 13.56 88.5 11 25.73 6965 n 3 114.456 118.141 118.693 165 37
Let's toss the highlighted rookie run and the push start as outliers, then separate by jet size -
On the 180 “rich” jets, my best speed was with a bit of help from a 9-10 mph sse wind, and we'll toss those –
12-Aug 14:28 88.9 8 25.7 7008 s 4 109.781 114.844 115.886 180 37
12-Aug 17:08 89.8 7 25.66 7106 ese 9 111.12 115.185 116.698 180 37
12-Aug 18:42 90 9 25.65 7145 sse 10 112.234 117.155 118.069 180 37
13-Aug 9:25 71.9 31 25.78 5943 nnw 1 111.944 115.336 115.878 180 37
We leaned out the mixture - we'll dump the wind enhanced outlier -
13-Aug 15.29 88.4 9 25.73 6946 sse 5 113.319 116.444 117.293 175 37
13-Aug 17.57 91.5 6 25.68 7177 sse 11 113.586 117.161 118.257 175 37
Switch to 170 jets
14-Aug 11:07 79.2 22 25.77 6391 n 0 113.241 117.077 117.816 170 37
Switch to 165 jets
14-Aug 13.56 88.5 11 25.73 6965 n 3 114.456 118.141 118.693 165 37
Final dataset -
date time temp rh bp adj wind 1mile 2mile 3mile jet timing
12-Aug 14:28 88.9 8 25.7 7008 s 4 109.781 114.844 115.886 180 37
13-Aug 9:25 71.9 31 25.78 5943 nnw 1 111.944 115.336 115.878 180 37
13-Aug 15.29 88.4 9 25.73 6946 sse 5 113.319 116.444 117.293 175 37
14-Aug 11:07 79.2 22 25.77 6391 n 0 113.241 117.077 117.816 170 37
14-Aug 13.56 88.5 11 25.73 6965 n 3 114.456 118.141 118.693 165 37
I'm going to take some credit here - most of the actual "driving" of the car is in the first mile - the one mile numbers are consistent enough for a rookie.
Compare the two best 1-mile times - and note the adjusted altitude, and wind direction and speed -
13-Aug 15.29 88.4 9 25.73 6946 sse 5 113.319 116.444 117.293 175 37
14-Aug 13.56 88.5 11 25.73 6965 n 3 114.456 118.141 118.693 165 37
I think we were getting pretty close on optimal jetting. I never did anything with the timing other than to take out the rev limiter after the rookie run.
I know this does not lead to a conclusion, but I think it leads to a direction.
--- End quote ---
Sumner:
--- Quote from: Milwaukee Midget on August 21, 2014, 03:02:47 PM ---Absolutely - It's less than 2% difference - the only consistent feature being the higher the adjusted altitude, the faster the car went.
It's a small sample, certainly not absolute, and there are variables not accounted for, but it does indicate a trend in this particular instance.
--- End quote ---
Am I reading the first graphic wrong?
115.886 at 7008 and 115.878 at 5943 (about same speed but different DA's)
and
117.293 at 6946 and then a faster 117.816 at a lower DA of 6391
If those are right then maybe we are seeing something else come into play,
Sum
SPARKY:
highlights the old adage
clean cars like the cooler air---dirty cars like the hotter air
Milwaukee Midget:
--- Quote from: SPARKY on August 21, 2014, 03:34:04 PM ---highlights the old adage
clean cars like the cooler air---dirty cars like the hotter air
--- End quote ---
That's where I think it's heading in my case.
I also think the database is too small to make any absolute conclusions - especially if you throw in driver inconsistency - which I'll own.
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