0ft vs 1500ft vs 3500ft elevation effects on HP graphed

[ZimbutheMonkey]

So I recently got back from a road trip from Calgary AB (3500 ft) through Revelstoke BC (1500ft) down to Seattle WA (0ft) and I took it as an opportunity to get some data on elevation vs airflow readings.

My reasoning for doing so is that I've never seen anyone post data sets on elevation effects from the same car/same time frame for a naturally aspirated Audi. I know that when I was trying to tune my V6 it was always difficult to compare MAF readings from different cars at different elevations, so I thought this at least gives a reference point for anyone who is interested.

Sorry about the X axis, it's a bit of a mess as I was overlaying different .csv files. However, the pulls were all taken from 2800 RPM to 6500 RPM, so you should be able to get a general sense as to where the RPM's are by looking at it in terms of 1/3=1000 RPM.

Car is bone stock other than an ECU tune and the deletion of the airbox flap. Also, I recently unjammed my intake manifold flap, so I know that it was functioning properly at the time of testing.

As well, IAT's are listed below, they are all within 4.5C of each other, so ambient temps weren't a significant factor in determining the air density.

0ft: +6C
1500ft: +1.5C
3500ft: +4C

As you can see, it's a pretty dramatic difference. On average 1500-3500 ft makes about a 20 g/sec (approx 25 CHP) difference and 0-1500 ft widens the gap by about 25 g/sec (approx 30 CHP). All said, it's about a 55 CHP difference between 0-3500 ft which seems to validate the air density calculations I've seen online.

On a sidenote, I know that dyno numbers for these engines vary quite a bit and the opinion of some is that Audi overrated them at 340 CHP.

That said, if you use the MAF/.08 rule of thumb, you'll note that the peak 280 g/sec readings at sea level equates to roughly 350 CHP. This suggests to me that the 340 CHP factory rating for the 4.2 is accurate.

I suspect in addition to elevation, ambient temps and dyno variance, that some of the low dyno readings may be a result of factors such as bad manifold flap actuators, poor cylinder sealing (as the 4/2 is prone to oil consumption and cylinder scuffing). However, it's nice to see that this engine appears to be a healthy example of a 4.2 (knock on wood lol)