Tuning at high altitudes

[RANeff]

I know not many of the Teams out there have to worry about this, but those that are located at high altitudes, how are you compensating for competition altitude? (were at ~5300ft)

Last year, we had huge problems getting the car to run right in Cali, and resulted in poor drivability and even worse fuel economy.

I have built a new baro correction table that I feel will help, but even then, I feel that due to the restrictor, things are not going to be optimal.

Short of leaving for competition early and re-tuning, Im just interested in what others who are in a similar situation get around the disadvantage.

P.S. we're on a Megasquirt, so its algorithms are not optimal for this sort of thing.

[RANeff]

I know not many of the Teams out there have to worry about this, but those that are located at high altitudes, how are you compensating for competition altitude? (were at ~5300ft)

Last year, we had huge problems getting the car to run right in Cali, and resulted in poor drivability and even worse fuel economy.

I have built a new baro correction table that I feel will help, but even then, I feel that due to the restrictor, things are not going to be optimal.

Short of leaving for competition early and re-tuning, Im just interested in what others who are in a similar situation get around the disadvantage.

P.S. we're on a Megasquirt, so its algorithms are not optimal for this sort of thing.

[Whis]

Are you running Alpha-N or Speed Density?

[Mbirt]

Wow, 85kPa. That really blows. Or sucks, rather. You guys are running speed-density and not alpha-n, right?

I found the baro correction table in Tunerstudio MS. Looks like it could be a good tool for improving starting with changes in altitude. It would be nice if the cranking PW's referenced barometric pressure. But they don't.

If the baro correction scales req_fuel according to the values you've entered, I would be wary of what it does to the rest of your fuel map that is still applicable up to 85kPa, however. Hopefully it's been coded to effect all parameters of operation except for those which already sense MAP for load.

Is there a way you could tune in a highly chilled environment? You could tune at a temperature low enough at your elevation to mimic the density of air 90 degF at sea level. Those top end values could then become the few lines above 85 kPa for your VE and Spark tables.

[RANeff]

Alpha-N, speed density was just terrible, because we draw very little vac, and the vac signal is basically nonexistant at and above 50% throttle.

(We idle at ~80 kpa up here)

That, and throttle response is way way better on alpha-n.

I was/am going to try a hybrid map with speed density below ~50% throttle, and alpha-n above.

[Jersey Tom]

IMO leaving a day early and getting some time on a dyno and/or track will give you the best result regardless rather than relying on how well things extrapolate.

I recommend getting some wings at Jim's and thinking it over.

[B Lewis @ PE Engine Management]

I would use Alpha-N with MAP compensation and a heavy filter on the MAP signal. The MAP comp table can be left as a linear relationship between fuel factor and MAP. Then if I were in your shoes I would also add another baro sensor for ambient compensation as well (or latch the MAP sensor at startup).

[Whis]

I don't know what ECU you are using, but I'd just run the MAP sensor as an atmospheric sensor and have it read atmo pressure directly.

Then, apply a atmospheric correction to your Alpha-N table based off of what the now Atmo Pressure sensor (as opposed to MAP Sensor) is reading and that will correct for altitude changes. Changes in ambient pressure *should* be fairly predictable for changes in fuel Req'd. Kinda depends on whether your VE changes at all for same throttle pos vs different altitude (pressure) or if VE responds Linearly to changes in altitude (pressure) vs same throttle position. If it responds exponentially or some other function, I'd say there is no way that you'll be able to get it tuned quickly besides running at different ambient pressures.

Nebraska isn't to far away. Why not trailer the car/engine there and run it there?

Whis

[VFR750R]

If you're tuning your spark map at high elevation, you will need to take some timing out at sea level. I don't know that there are any rules of thumb per in Hg change, but I wouldn't be surprised if it's as much as 4 or 5 degrees.

The difference in fuel should be pretty straightforward, but transients may be off a bit since WOT wall film will be different at different elevations.

[RANeff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by B Lewis @ PE Engine Management:
I would use Alpha-N with MAP compensation and a heavy filter on the MAP signal. The MAP comp table can be left as a linear relationship between fuel factor and MAP. Then if I were in your shoes I would also add another baro sensor for ambient compensation as well (or latch the MAP sensor at startup). </div></BLOCKQUOTE>

This is basically what I have set-up as best I can. I have two map sensors, one for MAP, one for ambient. The baro table I made is linear, which is additive on the base VE table.

However, to know exactly how much extra fuel it needs is up in the air 'till I actually get to tune at lower altitudes, if I can get the time at all.

Thanks for the ideas guys, maybe someone has some more experience? What did you guys do over at CU Tom?

[Jersey Tom]

We would always leave a few days early for competition, and use the time to scuff tires and do our engine map tweaking for the altitude change.

Seemed easier and more straight forward to just spend a day or few hours doing that... rather than spend however much time in Boulder trying to come up with some compensation that we wouldn't know would be good or crap until it would be too late.

[RANeff]

Being that competition is on finals week, I just dont forsee that happening! Ill just have to see what I can do to get out to nebraska or something

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
We would always leave a few days early for competition, and use the time to scuff tires and do our engine map tweaking for the altitude change.

Seemed easier and more straight forward to just spend a day or few hours doing that... rather than spend however much time in Boulder trying to come up with some compensation that we wouldn't know would be good or crap until it would be too late. </div></BLOCKQUOTE>