After a long hiatus, I've decided to create a thread to chronicle all the updates and developments I've put together for my 1er over the past few months. I've given much thought to improving several aspects of our driveline, and came up with several useful observations and - dare I say - new ways of doing things that I figured I would share with the community. So without further ado, here goes:
N53 head + Schrick cams
The biggest bottleneck in the N54 when it comes to making power lies in its cylinder head design. Optimized for peak torque at very low-rpm, it becomes more and more of a restriction as more air is pumped through the motor with increasing piston speeds and pressure ratios. Even porting it for all its worth isn't enough, as the exhaust port outlet is simply too small @32mm ID for a 500cc cylinder, leading to choked flow and excessive pumping losses on the exhaust stroke. The Mitsubishi 4B11 on the other hand (a good example of a modern high-performance 500cc/cyl FI design with similarly sized exhaust valves) runs the equivalent of a 36mm exhaust port, just for the sake of comparison... The intake side isn't all that much better, with a 22.x mm venturi feeding a 31.4mm intake valve, with a horrible short-side radius which really kills high(er) lift flow on the N54 head, far from ideal once Schrick cams come into the picture... So I looked at other BMW NG6 cylinders heads for inspiration. The N52 comes with a very nice CNC ported head, a la S54, but lacks provisions for DI. Now the N53 on the other hand, available in a 90PS/L variant in its ultimate form, runs bigger valves than the N54, and best of all runs the very same DI hardware we do. So I figured surely this was worth a closer look, and went out and procured one to see for myself, and what I found was very encouraging. Pros : +0.6mm intake valves, +1mm exhaust valves, +4mm exhaust ports, 28.x mm venturi on the intake ports (ideal for a 32mm valve), and a nice sharp recessed divider on the intake ports, similar to what you would see on a modern bike engine. Best of all, stock N54 intake manifold bolts right up! Cons: Coolant passages in the deck are different, exhaust manifold flange is different, meaning custom exhaust manifolds are a must, head bolt holes are 1mm too small a la N52, and custom washers for the head bolts need to be made. So it became clear to me that I would have to do whatever it takes to make this work, as the pros easily outweighed the cons in my mind. Of course having a shop complete with machinist and fabricator might have had something to do with it..
Unfortunately, for reasons which escape me, I did not document this process and only have 1x photo of the (as yet unassembled) head before it went on the motor... I will have more in the near future as I am preparing two more of these heads to go out to customers in the US, one of whom will put it on a flowbench to compare with his existing ported N54 head, I am expecting ~23x cfm @ 0.45" lift @ 28" on the intake, and ~185 on the exhaust, so watch this space!
Just for the sake of reference, I have also included a dyno plot of a stock N53, with catless headers, tune, and an N54 intake manifold, notice how it makes almost 100PS/L , and how power keeps rising with rpm while maintaining a very flat torque curve... Food for thought eh?