what to change on altitude correction.

[kaeman]

I tune at an altitude of 225 ft above sea level. I have my engine running pretty good with high load afrs of 13.4 to 12.7 without ego correction above 90 kpa. I went to the local dragstrip Saturday night it is at 500 ft above sea level. I forgot to turn on ego compensation and made my passes, the afr for my runs were 15.4 to 14.3.... not exactly power making numbers. how should I adjust my barometric correction curve to reflect that I was too lean. I used to go to reno but then the engine was 17.5 to 17.2 lean at idle and I just quit going, didn't want to see if I could ruin the engine.
first file is current msq, second file is at race track, third file is test launch before going to track.

idle stumble fix analyzed3.msq

2014-08-02_second pass redding_modified.msl

2014-08-02_10_modified.msl

[dancrev]

Not an answer, but the change in atmospheric pressure from 225ft to 500ft is tiny... less than 1%. I don't see how that can cause the 13-15% change in AFR that you are seeing. I don't know how much it affects AFR, but maybe humidity could be a factor too?

-Dan

[slow_hemi6]

In this case the correction is due to MAT. The second log is showing a much higher MAT. I don't know if it was heat soak from the drive to the strip or just from waiting to stage, but there you have it. It is indicating around 140f/60C and I have also seen 65C MAT on my car when ambient was more like 30 outside due to just sitting idling for a while. When moving obviously the engine is not ingesting 65C air but the ecu thinks it is due to the sensor heat soak. It gave me the same kind of issue you are getting along with hard starting as well. I ended up basically changing my Mat air density table so that it was 98% at 30C, 96% at 40C, 94% at 64C and 92% at 80C. You might need slightly different correction but it will be much flatter then the standard in that 30 to 65C range. This is not really a great idea for a boosted car as intake air temps can actually get that high under load.

[kaeman]

I was also surprised by the change in fueling, I didn't think that 275 ft. of elevation change should have made that much difference in the fueling. Looking at the datalog from the track it looked like the baro correction was 92 to 88%. The air correction was also 92 to 87%. I was looking at the online density calculator data from the track for air density and such, like today it was 78 degrees and 64% humidity 500 ft elevation, the air density altitude is 2406 ft. I didn't check it before going to the track so I don't know what it was on Saturday night. that could be messing with things also. but I think if I make a couple changes to the MAT density table it may help a bit. I just wonder how much change the baro was giving in addition to the MAT changes in fueling.

[suberimakuri]

Do you have a second baro sensor?
We found some intake air temp sensors better than others for reacting quickly to change from sitting to pre stage burnout. Open not closed IAT I believe.

[kaeman]

I don't have the second baro sensor. Just using the main sensor check at power up.

I am using the open element iat sensor. I thought of that also. I think the problem is I have never actually tuned the baro correction curve to fit my engine, I also think that the mat curve might need some adjustments for my engine...

[nathanhardy]

any info you can add that you've found in your tuning I'm having this same problem except I'm turbo and I know its my mat air density curve.. how did you tune it.. I e lower the curve or raise it

[kaeman]

I went online and found the MAT temp adjustments from the motec unit and just changed my MAT table/curve to those values, the engine liked the extra fueling, motec doesn't pull as much fuel out with the rise in temp. Look at my attached tune. I am thinking I will go out to a local lake where I can get an altitude change easily and do a couple of manual tweeks to the baro correction curve and bring my fueling up, whenever I go up in altitude my engine runs lean. so the baro correction is taking to much fuel out.

rescaled afr table 8-21-14.msq

[nathanhardy]

I went online and found the MAT temp adjustments from the motec unit and just changed my MAT table/curve to those values, the engine liked the extra fueling, motec doesn't pull as much fuel out with the rise in temp. Look at my attached tune. I am thinking I will go out to a local lake where I can get an altitude change easily and do a couple of manual tweeks to the baro correction curve and bring my fueling up, whenever I go up in altitude my engine runs lean. so the baro correction is taking to much fuel out.

rescaled afr table 8-21-14.msq

so being a turbo car I hardly ever see mat temp lower then 90+ and most of the time with heat soak I see 110 do you set the middle at your average temp?

[kaeman]

I don't know where you would set the middle, all I know is that I am adjusting mine until I am getting the afr targets back to where they are supposed to be. I have increased the fuel in my temp bins until it is giving me the same afr readings when the MAT goes higher as it was when the MAT was at the tuning temp. so far I have been having to increase the % numbers to bring back the target afr's. because the ideal gas law didn't work for my engine... it was removing way to much fuel and my afr targets were going lean. My idle afr is usually about 13.8 to 14.2 when warmed up but not heat soaked. when I went to the races and the MAT went high.. my idle was about 16.4 to 17 afr. so I had to add fuel to that heat range to bring the afr back to 13.8/14.2

[kaeman]

I have been making changes in the MAT adjustment curve and the engine is responding favorably I also just decided to extend my tables resolution for load bins by using table switching.
Here is the new tune.. I am hoping to be testing Saturday or sunday with this tune and datalogging.

2014-09-03 table switching.msq

[suberimakuri]

Thanks Kaeman, tried hunting for motec curve but haven't found it, so pulled from your tune.
Update, here: www.motec.com/raceseries/FSAE/

[kaeman]

I did some test driving today and data logging with the new table switching tune. I disabled the o2 corrections and did my test drive with the engine warmed up but no heat soak in the manifold, the unit ran great and the afr's were more stable without o2 correction than with o2 correction. Then I turned off the car and let the engine heat soak, made the same drive data logging and then came in and parked the car with the engine running to make the heat soak a problem, let the vehicle idle about 15 minutes and then went for the same test drive as the previous runs, the afr was stable and the vehicle ran great, I think the new MAT correction numbers in this tune helped a lot. I will have to trim the data logs and post them tomorrow but the current tune is attached.

Also my barometric pressure when I was testing and doing most of my tuning is at 98.5kpa to 100 kpa. today was 100 kpa.

my engine is a 383 small block chevy with 50mm(2 inch) ITB's I am using SD for fueling calculations, this is the tune as I have it in the car right now... I am going to manually adjust the ve table fueling in a couple spots that were running rich. in the 85 to 89 kpa areas of the 3600 to 4000 bins of the ve table.

2014-09-06 ve table switched.msq

[slow_hemi6]

Just had a quick look and it looks to be the same mat correction I use, also as per my original reply to this thread.

[kaeman]

Hey Slow,
I ended up getting closer to your values every test drive so I ended up using the values you gave me and it works much better for my engine...
This weekend hoping to hit the drag strip and adjust the baro corrections for that elevation, buy seeing what my target idle is and then adjusting the baro correction curve to bring it back to the 13.8-14.2 area.

[strain]

Hi Kaeman, Hi all!
I want to add a point to this discussion. When you have changes in altitude you always noted an a decreased number in map reading at WOT ( in you case yo have a first map average reading of 96.7kpa and an a second average reading of 93kpa ) taking a look to your VE map table I noticed that you have a big diference in the value of the cells in the specific rows from 90 to 100kpa, you don't want 2 ve tables to fix your problem, you don't need more resolution but less resolution helps you to solve this issue. I recomend you to don't do any baro correction yet until you fix this issue. I hope this point make sense to you and sorry for my english but I speak and write spanish.
Regards,
STRAÏN

[kaeman]

Hello Strain,
The reason for the big change in the ve numbers is that is what the engine wants at those map values, without o2 correction I am hitting my target afr readings under the hard throttle/ high load area of the ve tables. I have a smooth and stable o2 reading in the 90 plus kpa range of the ve table.... I think that the large jump is do to the engine cam and intake combo.

this weekend I will be going to the drag strip and checkout the baro differences... make changes as necessary.

[suberimakuri]

Hi kaeman,
Think Strain is talking about WOT map reading.
Where you tune normally is 98-100 kpa.
So at WOT you get those and ecu pulls appropriate row from table. Because your algorithm is SD.
At higher altitude , if your map is only 95 kpa at WOT it will read from 95 kpa row, however load will be very similar to normal 98-100 rows.
If your 95 kpa row is less , then engine will run lean.

Sure you can add baro correction , but that will apply a blanket percentage across the row.
If the shape of the row is different like your mid rpm range is.... then lean problems potentially.

Suggestion is to look at percent baro algorithm instead of SD.
That way at 95 kpa WOT, the ecu will compare with baro reading and use the 100 kpa(% baro) row. 95 kpa wot / 95 kpa baro =100 % baro row.
Then add baro correction on top of that. Make sense ?

[strain]

Yes, I'm talking about WOT pulls. I've live in Santiago, Chile ( 1.800ft ) and we have the mountains and the sea at 1.5hours driving I'm talking from 0ft sea level to 9.800ft in the mountain. When I go from the 1.800ft (Santiago) to Sea level ( Viña del mar ) with my Ve table fine tune, without ego correction and without baro correction I have very solid afr readings even at those big differences in altitude, Only when I go to the mountain ( 9.800ft) I need the baro correction on. Kaeman don't have more than 300ft of difference so I'm insist into modify your ve table wihtout activate baro correction. You have a big diference in numbers in the upper rows from 90 to 100kpa. Reviewing the logs that you attached I've notice that you have difference in your mat readings, this affects your air correction and of course your total fuel correction. I recomends you to turn off all the corrections (ego, mat, clt, baro, dwell etc.) and re-tune the ve table using 10kpa per row in the 80 to 110kpa (80-90-100-110kpa) range and do some pulls, I've notice that to fine tune an a ve table you need first of all turn off all the correction otherwise you allways have difference between pulls even in the same altitude because other factors.
If hope you can attach that logs.
I hope it helps you,
Regards,
STRAÏN

[kaeman]

I went to the drag strip and fired up the car let it warm up to operating temp and then adjusted the baro correction to bring the engine to the idle afr's that I have at my homes altitude. it took 2.5 % increase in fuel. my baro correction at 98kpa is 102.5%. I have been up to the track on two different occasions and the idle afr is correct and stable. I am going to load my car onto the trailer and then drive up into the mountains near my home stopping and checking baro correction curve, making adjustments, then continuing up the hill, making adjustments and continue up the hill until I have a pretty good baro correction curve.