Baro Correction Curves

[sedd]

I am looking to set up my baro correction and would like to see some curves from those who already have good curves entered. I believe If I see the msq I can gather up that info.

On a related item, after considerable searches and reading of posts, I am confused as to the general adjustment that takes place. In a recent response to a post of mine, I think I was told that the pulse width needs to be adjusted lower as a person goes up in elevation. For a given VE point, with the same map and rpm as the lower elevation, the amount of fuel injected at the higher elevation will have to be lower. The baro reading is smaller, and it appears there is less air cylinder filling efficiency.

I noticed and enjoyed reading the huge amount of effort about this item and wonder if there is any conclusion to be drawn?

[masterx81]

From my experience in my engine i've had to remove 7.5% of fuel every 15 kpa. So il at 100kpa of baro i have 100% of fuel, at 85kpa (~1400mt) i need 7.5% less fuel. With this rule i've also done a travel to 2000mt without any change in afr.

[sedd]

thanks masterx81,

So far your straight line is very close to the square root of the pressure ratio curve. The square root of the pressure ratio is used in orifice gas flow equations so maybe that is the general type of curve? More "real" correction data might support or add to your data. I have plotted this on a graph with other data and will repost that once (I hope) I get other data.

[sedd]

I found an article by Delphi Engineers that was very informative. For me it gave the answers to questions about what is affecting the VE as the baro changes.

I created a spreadsheet that uses the information for a naturally aspirated engine and set it up to allow for evaluation of settings that must be decided upon. I placed some information I was given and some I found on the net on it, to compare to the calculated values. There appears to be a pretty good match. More actual versus calculated data is needed.

Both back pressure and an exponent needs to be decided upon. At the same time there is not a huge difference in the curves with variation in settings chosen, also shown by the spreadsheet.

Go to the internet and search on 2009-01-0587, and look for the .pdf version or look for the Delphi site and find it there.

In summary, there is an equation they offer that uses exhaust pressure and intake MAP with the baro to come up with a correction for the baro. that was used for setting up the spreadsheet. I also used the suggested value for the exponent.

This is a good read for turbo charged engines and might help out that effort quite a bit.

If it is decided that this equation and curves are useful and a good fit to what really works, there is another correction that could be made to reflect the change in exhaust backpressure with VE or with RPM, and to use that to further make corrections on the baseline curve. Since the curves are nearly straight lines a simple multiplier can be entered for any given VE. I feel VE should reflect backpressure in a linear way?