entropy
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posted May 28, 2009 03:07 AM
density altitude: corrections to fuel table to keep right AF?
I am double sure that there are folks on this forum who measure/calc density/alitude and make changes to their fuel maps accordingly.
I am a complete noob here, but losing a motor at Texas Mile almost surely due to running lean has me wanting to learn about DA changes and how much fuel to add/subtract to keep AF 12.5-ish.
The motor config must make a difference, but any starting point/directional info would be much appreciated.
Anyone wanna share??
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2000redrocket
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posted May 28, 2009 05:33 PM
ent are you talking about the AA reading? at maple grove it gives barometer, temp,humidity and a AA i think is actual altitude the air is like. if this is it a 500ft drop had my afr go .2 to .3 leaner. i actually pulled the bike to the track last time and got all runs from the loggger at .1sec scan. sucks the truck gets 20mpg on diesel and nings gets 36 to 39. i hate pulling the bike there.
i will let you know if my ecu does not fix the afr as the temp rises higher than last time.
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2000redrocket
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posted May 28, 2009 06:12 PM
 Edited By: 2000redrocket on 29 May 2009 02:21
for engine saftey someone on this forum could come up with a gismo that reads the output voltage from the wide band o2 sensor at whatever you set it at to pull in a relay to either cut out the engine or light one hell of a this is bad light so you shut down from your run. say your going to melt it afr actual dc voltage. i will ask my brother but it may be past him. i had the idea though.
http://autospeed.com/cms/title_The-Simple-Voltage-Switch/A_2476/article.html
looks like it is 32 bucks plus shipping. it is a steal on what you can do /protect with it.
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TRNorBRN6001
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posted May 29, 2009 07:33 PM
Some engineer has to have this in a book somewhere!
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2000redrocket
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posted May 29, 2009 07:39 PM
to go .2 to .3 richer or leaner i would only move my ecu numbers 2 higher or lower. going 5 if you are close is too much and will go past .
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whitehendrix
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posted May 29, 2009 08:47 PM
so, are you looking for an auto-corrective measure or math to manipulate the map depending on altitude and "weather" related numbers?
i'm sure something can be concocted out of the standard numbers available for pressure drop per X feet and temp drop per X feet and all that.
an A/F based "oh shit" light would probably be easy if the thing logs and has a programmable alarm channel.
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tcchin
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posted May 29, 2009 09:00 PM
Edited By: tcchin on 30 May 2009 05:11
I have some HRC setup data for carbureted 600cc Supersport engines. While the numbers themselves would be all but useless, the trends should be universally applicable. The setup data is arranged in a chart with ambient temp ranges listed along the horizontal axis and altitude ranges listed along the vertical axis. There are four temp ranges listed: 39-59F, 59-75F, 75-88F and 88-100F. There are also four altitude ranges listed: 0-999', 1000-2499', 2500-4999' and 5000-7500'.
As you would expect, the jetting numbers are richest at sea level and 39-59F and leanest at 5000-7500' and 88-100F, which is the diagonal path across the chart that goes from the lower left corner to the upper right corner. What's interesting is that the opposite diagonal coincides with a path of isoparametric jetting. In other words, your fuel demand at sea level and 88-100F is nearly identical to the fuel demand at 5000-7500' and 39-59F, and everything in between along that isoparametric diagonal line.
For every other cell in the chart, one change in range, whether it's ambient temp or altitude, will require a one-jet-size adjustment, or about 3-4% in overall mixture strength. (I suspect that the chart was configured this way on purpose.) So, if you used Andy's dyno on a 100F day to set up your fuel map, then went to Goliad for the Mile and it was only 65F, you would enrich your mixture by zero elevation cells and two ambient temp cells, which is two jet sizes (or 6-8%). However, if you were to go to Willow Springs on a mild spring day instead (2300' and 75F), that would be one elevation cell leaner and one ambient temp cell richer, or no net change in jetting.
YMMV. Use at your own risk. Do your own research before you risk your motor to something you read on the internet.
http://www.buckeyeaviation.com/manuals/mainjet.pdf
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tcchin
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posted May 29, 2009 09:08 PM
I would think that the "oh shit" light (OSL) would get a quicker and more accurate signal from exhaust gas temp. EGT is very well documented within the aircraft industry, and an EGT-OSL may already exist.
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2000redrocket
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posted May 29, 2009 09:27 PM
true egt has been around but reading about that card all you have to do is adjust the pot to the voltage of the bad afr and you can use the relay for anything you can dream up a diagram for.
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entropy
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posted May 30, 2009 04:20 AM
Edited By: entropy on 30 May 2009 12:35
Tim: that sort of relationship is what I am after, change in "air" = approx change in fuel map
I am hoping that rather than viewing temp & pressure separately, i can use 1 number, DA, to set up the relationship.
Yesterday i got my Kestrel 4250, and this morning i did the deed that every man dreads: read the directions, ugh!
in the setup process found out something cool, Google earth is able to show you elevations for any point on earth with damn cool resolution. It shows a known 10' change in elevation close to my house, COOL!
Now i can see temp, RH, barometric pressure, "real" pressure, altitude, Density Altitude.
This am i'll go to Andy's and test the ARC-2, but also note DA associated with the resulting fuel map.
After a while maybe i can establish a relationship: change in DA = required change in fuel map, like what 2000rr said..
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entropy
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posted May 30, 2009 04:33 AM
quote:
ent are you talking about the AA reading? at maple grove it gives barometer, temp,humidity and a AA i think is actual altitude the air is like. if this is it a 500ft drop had my afr go .2 to .3 leaner. ....
yep,
this is what i am talking about
thanks 2000rr, somehow i missed your input earlier.
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tcchin
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posted May 30, 2009 04:47 AM
Karl, I agree that DA vs fuel is the goal, but the only hard data that I had was temp vs altitude vs fuel. If nothing else, it's just another data point. Going back to aircraft, there are probably a lot of DA vs fuel charts available, as pilots live and die by that info. I'll see what I can find.
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2000redrocket
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posted May 30, 2009 05:29 AM
i imagin wonce you get the da chart in use for a while you can remove all their numbers and plug in your either pc or ecu numbers and make it cut and dry on the number to enter in the chart..have fun entropy.my fun got rained out last night. now a two week dry spell unless i go to maryland once.
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entropy
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posted May 30, 2009 05:49 AM
quote:
i imagin wonce you get the da chart in use for a while you can remove all their numbers and plug in your either pc or ecu numbers and make it cut and dry on the number to enter in the chart..have fun entropy.my fun got rained out last night. now a two week dry spell unless i go to maryland once.
how about Loring 1.5mi Aug 1-2???????
just slap 18/44 on it and FLY!!!
It would be great to finally meet you, see yr set up.
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entropy
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posted May 30, 2009 05:51 AM
quote:
Karl, I agree that DA vs fuel is the goal, but the only hard data that I had was temp vs altitude vs fuel. If nothing else, it's just another data point. Going back to aircraft, there are probably a lot of DA vs fuel charts available, as pilots live and die by that info. I'll see what I can find.
Tim, i wasn't running down yr ole method, just tring to simply for my alcohol & drug addled, calcified brain. Good luck on the dynos today!
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tshultz
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posted May 30, 2009 09:06 AM
quote:
quote:
i imagin wonce you get the da chart in use for a while you can remove all their numbers and plug in your either pc or ecu numbers and make it cut and dry on the number to enter in the chart..have fun entropy.my fun got rained out last night. now a two week dry spell unless i go to maryland once.
how about Loring 1.5mi Aug 1-2???????
just slap 18/44 on it and FLY!!!
It would be great to finally meet you, see yr set up.
Ive been trying to talk him into it.
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