Ok so here's my experience from tuning these cars. If the turbo has headroom to boost more and compensate for altitude, then it can almost make the same power. But, the turbo will spin almost 20% more rpm to make the same boost. It will generate more heat and may move a few notches away from the efficiency island it's in at sea-level.
But let's assume all of that is academic and for all intents and purposes it makes pretty much the same power. All good. So stock cars have ample headroom and the stock M4 has such a good turbo that it can boost the extra it needs at altitude and make the same power without any significant overhead.
But when it's chipped it can't. I am boosting 22-24psi up here on the M4's I tuned. The turbo is maxed and on the limit. IAT's go from like 35deg to 65deg in 2 gears. That is a tell-tale sign that the compressor wheel is too small for the boost and generating excess heat.
At sea-level it will make that boost easier and quicker and with less rpm and less heat. And it WILL make more power. And I can prove it because our car ran 11.4 @ 206 at Matuba. I tuned this car at altitiude on KAR's dyno and it made 335kw. I vboxed it and it ran 196. Nothing has changed on the car and it ran 206km/h at Matuba. So the exact same car with the exact same tune picked up 10km/h from altitude to sea-level. And this is common not just for the M4, but other cars we have done like K04 Vw's. They also pick up 10km/h from Tarlton to Matuba. It's just the nature of sea-level air vs rarified highveld air.
The car I ran at ODI makes 355kw and exited 200 at ODI. It is 20kw stronger than the car we ran at Matuba. So I'm looking forward to coming down and running a time at sea-level with one of our stronger cars. And I love the comraderie and competition, always have. It's what makes all of us better and improves our game and the level of performance for BMW's. Win-win, even if you lose because it forces you to come back stronger. Bring on the 10's!
Sorry clean forgot to add. I absolutely agree with Junaid that if you run at a prepped track up here then the massive advantage of the extra traction makes up for the power loss and you can make up the time. Absolutely due to the fact that if you can drop your 60 foot time with good traction at a good track then that translates to much better momentum and a better time.
but the problem is we ran at an unprepped ODI and there the traction is much worse than Matuba. Matuba is known for very good times and loads of FWD and RWD have run even world record times there so it's a fast track with good traction.
opcorn:
