Road racing is a wholly different animal than drag. Even time attack, while closer, is not the same thing. Imagine running an N54 in a 2 hour road race. Impossible to consider at the moment. It's not a turbo problem. The N54 world revolves around the turbo as the center of its solar system. I'm not addressing you specifically, @berns of course, just jumping off the distinction you well pointed out.
There are only so many S-engined E92s to go around. S54 M3s are climbing in cost, while availability diminishes (we saw this with the E30 M3 in the late nineties). The E36 is about to go the way of the E30 dodo bird. So in the long haul - unarguable - none of these are market level solutions. One-offs ... sure people can go swap all they want.
The first issue with road racing is reliability. This comes in two primary issues: 1) Heat is the killer. a) The N54 cooling system is not old school - this idea of throwing hardware at the cooling system is 20 year old thinking with little understanding of how the N54 cooling system works - with electromechanical cooling, tables with non Ve targets, and likely adaptive and predictive algorithms to control temps. Oil coolers are even more foolishness to that - if one can't tame the cooling system (primary job is cooling), trying to tame it by cooling oil (which cooling is an oiling system SECONDARY function) is fruitless in such a pursuit. That is, fruitless without addressing the core controls. Some programming is needed because the cooling logic for the N54 is in software and controlled at multiple points. b) Furthermore, the E90 likely has some packaging problems in road racing trim. That old saying, "10 lbs of shit packed in a 3 lb bag". The packaging is a long conversation, exacerbated by oversized FMIC installs, piping, a very imperfect engine intake air routing design for this application, etc. c) the head is designed to support characteristics BMW thought necessary to bring its customer base into the turbo world. But the 165 cfm head is horrible for road racing - causing the need for higher turbo pressures than we want (and more heat). Maybe with the N53 head one can get 500 whp on pump gas under 20psi? Heat is the monster to tame. 2) Turbos that are motorsport grade are the next issue (they exist but the market has not existed for the N54 - this is a cart/horse problem). @[email protected] was looking at the Garrett GTX 550 small frame turbos, for example, but Garrett has been dog slow in releasing the IWG versions. Other possible solutions may exist - but not much proven out so immature as a solution space in twin mode.
Second the E9x suspension, particularly in the rear, has not seen the kind of development necessary to put the kind of power down the N54 can deliver - consider momentary power exiting the apex is likely 2x what the typical NA BMW HPDE car makes. No one has seriously addressed the rear suspension for this application. And 98% of the "old school" BMW road race people have no clue about anything past an S54 - that's about 2006. Two fundamental issues - the E90 suspension is revolutionary design (not evolutionary) from the prior BMW designs. Next, managing 500whp or 600 ft lbs, not to mention nearly instantaneous torque off an apex is beyond foreign to any BMW road racing specialist - they fairly well haven't dealt with this.
The good news is lots of development continues on the N54 platform. There is work underway on all three of these fronts - cooling, turbos, and suspension - for road racing application. Other work being performed, such as with advancements in fueling support that allow higher horsepower DI native, will also contribute to a potentially reliable road racing setup. Too early to say if this all comes to fruition. But then again, I wouldn't count it out just yet . Anyway above is my conjecture ... it's also part of what brought me to this platform from the old school BMW world: kind of feel like a foreigner in what should be my father's land lol.
BTW great discussions on this thread - thanks @martymil and @Hydra Performance for all the back and forth. I gave up on the idea of just repeatedly pressing like button on all the thread posts.
I had some guys (that track their 335is) try to tell me off on Facebook a few months back because I said this platform is not ideal for tracking. It's just not. Honestly. BMW did not put a lot of "track ready" development into this car compared to the E9x M3 and it totally shows. It doesn't even have LSD from the factory.
My S2000 and Evo were great track ready cars with platforms that emphasized being used on track. This is a platform you have to Frankenstein into being tracked.