siko said:
Next step would be widening the turbos!
Now that would be the challenge. I have no doubt that one can easily get an additional 40-50 extra HP from the current configuration.
Getting anything more will require doing the following:
1. Increase the boost pressure which will entail the turbines spinning at higher speeds. The draw back here is that the efficiency-window (bandwidth) might be exceeded, rendering the turbines inefficient beyond a certain range.
2. Increasing the size of the impellers. Now widening of the Turbos, or increasing the bandwidth will require using bigger impellers & configuration. The moment you do that, you will have a bandwidth that will shift to the high end, and that inherently comes with Turbo-Lag, and other heat related issues.
This is my opinion(there are many more reasons why they went this way) on why BMW used the small blades:
1. Pratically eliminate Turbo-lag (still occurs at very low rpm, but eliminated at 1300 rpm). Small impellers require small force to spool due to the low inertia. Small impellers however gives you a low bandwidth thus the 1300-5000 rev/min range. Beyond a certain rpm the turbine will lose its efficiency- in the case of this engine, it is set at 5000 rev/min.
2. Reduce the Turbo-cooling cycle associated with impellers. Turbine blades produce very high amount of heat, and the bigger the turbine for the same revolution the higher the operating temperatures, hence you need to have a way/procedure to cool them. Because of the small nature of the configuration in the N54 engine, you can treat it like a normal engine without going through of the old rituals.
For all practical purposes, I honestly do not see many people pushing beyond 5000 rpm on sixth gear. On the N52 engine, that equates to over 130mph
Now nothing stops someone from coming up with a light-weight-heat-resistant material, that will allow engineers to use bigger blades and open the bandwidth by 1500 rpm, and simulataneously eliminate Turbo-lag. Nothing stops someone from using materials to design a variable angle impellers that push the bandwidth even further.
But right now, this is the conundrum.
for $1200, I'd take that for sure. They don't change a single thing on the engine, just update the computer a bit. That 400 hp version sounds quite interesting too.
