I agree to some extent. I live in UT (4500ft) and when i go to CA i will have to retune, unless we can at least have some sort of setting that we can change for atmospheric pressure. Doesn't seem like it would be too hard. But what do i know.

 

A variable resistor will allow for enough adjustment to compensate for altitude if needed.

 

If this setup reads absolute pressure rather than gauge pressure, it shouldn't matter. At higher altitudes it would read lower pressure and lower altitudes higher pressure and would therefore would calculate the correct airflow. With a blow-through setup altitude could cause a problem, but with full speed density it shouldn't make a difference.

-Paul

 

i guess in the end it would matter. the air density required to make a certain boost number at a certain altitude is not the same for all altitudes and the air mass being different in each case will cause some problems when going cross country.

how does honda do it? they keep the baro?

 

That would be true for gauge pressure, but would it still be true for absolute pressure? I'm not sure how it's done with speed density in the stock ECU, but with the MaftPro the manifold pressure measured is absolute. When your boost gauge reads 20 psi at sea level, so will the MAP sensor. At higher altitudes the boost gauge may still read 20 psi but the MAP sensor may only read 18, therefore compensating for the altitude.

-Paul

 

Speed density has to be based on MAP and not gauge pressure. The air density in the manifold is proportional to the absolute pressure and absolute temperature of the air in the manifold. Load will be calculated from that estimated air density and throttle position. A car tuned in load or MAP control will show higher gauge boost readings at higher elevations. The engine will be under the same stress (load) at any altitude though.

I just took a quick look at my Evo IX disassembly. The stock Evo programming uses baro pressure in several different subroutines. I haven't tried to figure out what those subroutines do or what influence baro pressure has on the outcome of those subroutines, but it seems quite reasonable to me that a speed density Evo could run like crap if driven at an altitude different than what it was tuned at.

 

i retract my previous statement. the manifold should be likened to a closed volume. gauge or relative pressure is irrelavent.

 

For what its worth....

In my other car I run a HKS FCon VPRO standalone EMS. We no longer use the stock MAF sensor on that vehicle and it uses its own HKS/Denso MAP and IAT sensors. The HKS FCon has a "altitude compensation table" that allows the VPro to compensate for changes in altitude based on your elevation, so your tune remains the same, if not very close to its original tune regardless of location. Does ECU Flash offer anything like this, if not can it be implemented?

Hope this helps,

George

 

The stock ecu has it but I think it must be changed to be scaled against MAP rather than Baro and then you have air temp compensation also. I don’t know if you guys have any evos with 3bar map sensors and IAT stock .. mine is .. It came with an IAT sensor in the intake manifold and a 3bar map sensor.

 

^^^^

That is interesting, non USDM evos come equipped witha 3bar MAP sensor and IAT sensor....hmmm ?

 

If this is true, what is/are the part numbers for the sensors?

Maybe we can see if they can bolt right up/or make a spot for them so that we can have the ability to use the sensors if needed for this speed density conversion.

EDIT: I know the JDM MAP sensor is available to use, I am primarily talking about the AIT sensor.

 

I will take pictures of it on my way out of work and post it.

 

here you go guys .. i will try to get you the part number

 

attached is the calibration file for the stock IAT sensor.

Az

 

This is great info. Can someone use this to help us log IAT, simply by buying a Mitsu part and updating the ECU? ????