Here is my theory about rb3 and altitude overcompensation

[mulot30th]

The stock ECU compensate the elevation by leaning appropriately.


AND the rb3 sees less ABSOLUTE pressure for a given boost so by design it will compensate this too obviously.

so we have TWO altitude compensation that don't know what each other is exactly doing...... then you can imagine the rest....


Easy way to correct this would be the rb3 to have a atm pressure sensor and reference its tables in regard to BOOST/VAC pressures instead of absolute pressure. Doing it this way, the 10% (this is an example!) column would not shift as we go up or down in altutide...

 

[JIM]

But is the RB3 capable of this task? Have you tried this?

 

[mulot30th]

At it is now, NO its not capable as it would need another 1bar sensor to sense atmospheric pressure and have the required firmware (pretty simple, but still need to be implemented)

 

[longsled]

I'm agree with you. the easiest way to have a kind of fix is to use the switch map and have an other map 5 to 10% leaner or richer, and you can switch on the fly when you are at a different altitude.

cold or warm temp can also make difference and you can see different AFR'S from a cold day to an other. again, you can fix quickly by the same switchmap button.

 

[thamax]

you really need like 4-5 maps to switch between if u ride alot of varying elevation 2 just isn't enough

 

[longsled]

the biggest mountain here have 2500 ft! I'm at sea level.

 

[thamax]

i ride 4000-9500 ft out west in the rockies

 

[mulot30th]

in riding in bc last january, I noticed there is about a 2500 ft of gap in between times it need to be re-tuned to keep responsiveness and performance.

I tried to go from bottom to top without re-adjustment... the load levels do shift so much that sled is almose undriveable up top, it goes extremely lean. I am talking about a 7000ft+ spread.

I think I have a video showing that.... I may need to convert it to youtube.

Since I was new to rb3 tuning and did not knew this at that time... I spent most of my riding time in BC with a sled that had no bottom-end and no mid-range (did not knew why this happenned at time) and I ened up just tuning it WOT to at least be able to do some good climbs... which I did... but tree riding sucked badly

 

[JIM]

So what would happen if a different kind of sensor was installed. A sensor that was plumbed to the intercooler and didnt ever see vaccum? Like the sensor on the mcx. How is that mcx sensor different than the 3 bar gm used with the rb3?? If the rb3 is just reading volts in from a sensor then why cant the rb3 be replumbed to the intercooler? Or what would happen if the stock barometric sensor was plumbed to the intercooler? Mcx does/did this on their kits, would this help with over compensating on both systems?

 

[mulot30th]

I dont thin so.

Map sensors are always ABSOLUTE PRESSURE sensors from 0-5v


this way:

Sealevel: 25 psi of boost is in fact about 40 psia

At 7000ft: the same 25 psi of boost is about 37psia (a guesstimate please someone correct me if not exact number)


So the only real way to correct this situation is to have a BOOST/VAC referenced tables in RB3..

and have another 1bar sensor that would measure the atmospheric pressure so that XX psi of boost remains at same place on rb3 tables.


maybe we see this in rb4 in future?

 

[JIM]

 

[thamax]

has dave tried this yet to correct the boost table

 

[JIM]

 

[thamax]

so who wants to build these and make them water tight also so it can adjusted from the dash or something and have a voltage gauge thats waterproof so we make this system work flawless???

 

[JIM]