So, what's wrong with this picture?
It's as if the BMW engineers intentionally moved the motor forward from where it should be in this chassis. Of course, the reality is they didn't want to invest in a solution that took full advantage of the chassis. They pulled an E46 subframe out of the parts bin, added an S54 and the motor placement was the by product. In an E46, this motor is tucked up under the cowl about as far back as it can go. In a Z4, not so much.
I'm of the opinion that the forward location of the motor in this shorter wheelbase chassis is why it is considered not to handle as well as an E46. The shorter the wheelbase, the more pronounced the weight imbalance impact. My car currently has 51/49 weight balance. I've talked to a couple chassis engineers and they agreed with this premise.
So, my project this winter is rather ambitious. I plan to move the motor back 3 1/4" - 3 1/2" to prove or disprove this theory. I mean, it
should handle better, but it certainly won't hurt the handling. So why not? That measurement appears to be as far as it can go without cutting structural metal. The Z4 has a rather robust box section crowning the transmission tunnel entrance. If one were to notch this out, the motor could go back even further. But that would be risky. The last thing I want to do is compromise the wonderfully rigid structure of this chassis.
A dependency to moving this motor back is removing the dual pan wet sump oil system. It simply will not clear the steering rack. A dry sump system will give a flat pan and eliminate this restriction.
And so the fun begins...