Altitude Tuning

[Major]

I have a question about tuning at altitudes such as JHB. The books I've read don't really get into altitude compensation and just sort of breeze over the topic, but being in JHB I started to wonder. My question is how do you tune for WOT if you never have the same airflow/load/kPa as down at the coast? Do you just take what points you can measure and extrapolate it vertically for higher airflow rates at those RPM points, or what do you do? Obviously referring to NA cars. How do you do spark timing as well if you don't actually experience full load in JHB? Or have I misunderstood something?

 

[Raybimmer]

For 2c here goes :roflol:
If the air pressure is 17 per cent less than at the coast , then I would expect that cylinder filling is less dense , so wot could flow a certain cfm , just having 17 per cent less pressure .
Advancing timing in a non computer controlled car would increase power a bit, but may lead to overheating .If the ecu is adaptive it should be close to optimum efficiency .
If the volume is the same and the pressure is less then does less petrol restore the air fuel ratio ?

 

[zaleonardz]

Hoezit Altitude ?
:biglol:

 

[Major]

If the air pressure is 17 per cent less than at the coast , then I would expect that cylinder filling is less dense , so wot could flow a certain cfm , just having 17 per cent less pressure .

If you look at a MAP vs RPM table you'll understand where my question is coming from. At WOT in Joburg you'll only reach somewhere around 82 kPa whereas in Durban it would be 100 kPa. I understand that you can simply increase fuel with increased airflow on a MAF system, but what about a MAP system and it's VE tables?

Advancing timing in a non computer controlled car would increase power a bit, but may lead to overheating .If the ecu is adaptive it should be close to optimum efficiency .

Assuming the car in question isn't using a closed-loop system with a knock sensor, then.

If the volume is the same and the pressure is less then does less petrol restore the air fuel ratio ?

Well that's pretty much why I'm asking the question. Volume stays roughly the same (or a little less at altitude is my guess) and the air's less dense, so yes less fuelling restores A/F, but how do you tune for the coast while up in JHB, especially on MAP-based cars where you have to do the VE table measurements beforehand? And how do you do spark timing on a MAF/MAP-based car without actually seeing the power figures it puts out at the coast?

 

[George Smooth]

Are you asking the sponsor or the board in General. I can move the thread if you want?

 

[Major]

Are you asking the sponsor or the board in General. I can move the thread if you want?

I guess this can be a general question, but since Xcede do chip-tuning and such I was interested to find out from them.

 

[P1000]

The throttle position is only used as check and for enrichment on throttle changes, so it has not much to do with calculating the actual fuel to be injected 99% of the time, and when it dies have effect, it is just the rate of change that is used. With a MAF system, the mass of air entering the engine determines the amount of fuel. So, regardless of throttle position, the VE table will look up air mass/vs rpm which is the same at the coast or at altitude, with only never being able to reach the higher regions on the VE MAP at altitude. Then there is also trim values from the O2 sensor, which brings it very close to ideal in real world situations.