Ive been working on my tune a little bit (thanks to you guys here on EvoM ) This weekend Im going to the drag strip (Firebird Raceway in Boise, ID). I am currently roughly 2500-3000' higher in elevation than the track. And, obviously, this is where Ive been tuning. Im wondering what kind of changes I should expect. With what little tuning knowledge I have, Im expecting the AFR to get leaner, due to more O2 in the air. If I can get my AFR back to where Ive got here (roughly 6000' asl), what other things should I be looking at? Im planning to log my runs and tweak timing/fuel at the track. I will be getting into town tomorrow night (racing on Sat), and should have some time to gather some logs if the weather is good. But Im just trying to prepare myself for what I will need to do. Will I be more prone to knock, or less? About how much would you guys expect my AFR change? Will the temp compensation tables take care of most of this?

Oh, and I should also have a chance to test Lift shifting vs. NLTS (BIG thanks again Tephra!)

Thanks for any comments
-CB

 

I could be wrong we will let some other guys talk about this more but i think the "barometric" table should scale the fuel for the air density.



We shall see what the exports say.

 

Each time a piston descends it pulls in the same volume of air, but the mass of that volume of air varies with temperature, barometric pressure (elevation) and humidity. Chemically speaking, it is the mass of the air (oxygen portion) that determines the mass of fuel needed for optimal combustion efficiency (horsepower production). When tuned for a certain elevation and then drastically changes, it the MAS sees an altered amount of "air" which is what partially throws the tune off.

HTH

 

^^Thats pretty much my logic. But will the ECU compensate?

 

You should hit higher load cells if you're not using ecu-controlled boost.

An example, I had my error correction off on my boost and one cold morning I hit loads 20+ above my target at peak boost.

 

If you are using a MBC your boost will increase. Some EBC do not have a very good feedback and will cause your boost to increase. If you are using the ECU to control boost it should automatically compensate for the barometric changes. Key word being SHOULD.

 

Im using a GReddy Profec-B. And dont have a problem turning it down to compensate for the change in boost. Say I get boost dead on to where it is here. Im probably still going to have to tune the AFR again, correct?

 

You will probably have to make some minor changes to the fuel tables.

 

The ECU calculates mass airflow from the baro and intake temp sensors in the MAF.

So, if you change elevation to a higher elevation (lower baro), you will have less mass airflow/lower load values. The ECU is calculating the lower mass airflow because of the change in baro.

So, in a higher elevation, you may now be operating in parts of the map that you haven't necessarily tuned before. So, a few tweaks may be needed.


Eric

 

I will only talk about the two tracks in which I raced my Evos over and over. My constant, persistent,steady,unvariable and perennial results is that 100% of the times the Evos(My Evos) will run 2-3 tenth quicker and achieve 2-3 mph increase on the 1/4 mile. These results are backed up by multiple friends that raced from Tucson and Phoenix. The altitude makes great differences.


Spool up is quicker and boost raises slighty. The altitude difference in which I am refereing was 1850ft difference. Firebird Raceway in Phoenix is at 1250ft while South Western International raceway is at 3100ft.

Base on my testimony I would expect your car to be significantly quicker. Just for the record, the tune was not changed, just boost adjustment.

Additionally I also was able to dropped a full 5 tenth of a second and increase 4mph on a NA 91 Civic SI by going from 3100ft(SIR Tucson) to SAR(San Antonio at 700'. Botton line, expect good gains.

Carlos

 

So I should basically expect the ECU to start looking in the higher loads (which Ive tapered off while tuning the others)?

 

I noticed while on a recent road trip that while at sea level where I live my baro will log at 103%, and at 4000' it was 93 at steady state cruising. It was also about 20% less load when I did get on it comparing similar temps but different altitudes. Today I was seeing 285 or so at 22psi and then it was 260-263 at 22.5 or so.

 

Edit: I thought you were going to higher elevations...

For lower elevations, yes, you will have higher mass airflow and higher loads.


Eric

 

6052ft ASL here, and a baro of 84. Just for the sake of information.

 

Ask Warratalon or Evofunk, they know what time it is. They both raced at the same track in the NorthEast and they both lived in Colorado Springs(6000'. They can tell you first hand their experiences. Also they both have Dyno numbers that reflects the huge altitude difference. Their boost levels had to be readjusted drastically.

Carlos