Eric_Oz_S2

I have an interesting issue with my supercharged S2. The S2 does not have an altitude sensor like the turbo. What I have found is that at an elevation of 500m/1640ft, there is an increase in fuel/reduction in AFR by about 5%. This corresponds as it should with the calculated air density change at this elevation. What this means in practice is the AFRs are dropping from around 10.8 (tuned near seal level) to around 10.3. The 10.8 is about right for a forced induction (7 psi) engine with stock 10.9:1 CR. The 10.3 is getting a little low and I imagine I would be getting a double hit on power from both less density and lower AFRs.

I will be going to Bathurst in April, and the elevation there is around 700m, this will mean 8% richer AFRs, so my 10.8:1 will be down to 10:1. Is this anything to be concerned about? I think it may be but I'm not sure what others do in this instance. Perhaps I need to load a new map for Bathurst and reduce all the fuel maps by 5%?

It wasn't so much a problem when it was NA as the lowest AFRs were only around 12.

Any suggestions on the best way forward??

blown 944

what I do when I go from where I live to the dragstrip is to reduce fuel pressure slightly. The DA goes from 6000ft to 9000.

So far it has worked well for me

Eric_Oz_S2

I suppose I could rig an exteral switch to the fqs at the dme and adjust the maps so that this gives me the right injector factor for the altitude. I'm surprised at how sensitive Afrs are to altitude. I think it is about a 1% reduction in density for each 100m elevation. Does that sound about right?

blown 944

I'm sure it changes percentage wise the higher the elevation. Otherwise my car wouldn't run.

I'm curious what your cranking compression is with the car warm?

Rogue_Ant

The % change is not quite the same every 100m...

That said, you could use ~1.2% for every 100m, and that would get you close.

Eric_Oz_S2

Thanks - I'm unlikely to get above 1000m here in Oz, so I might just use -4% (four injector factor values lower relative to the current -20% base setting) connected to the FQS switch. Not sure how easy that will be to connect to?? I don't really want to cut it off.