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      04-11-2020, 02:52 AM   #2
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Drives: E90 M3 6MT
Join Date: Jan 2009
Location: USA

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2011.5 BMW M3  [5.00]
2004 BMW M3  [5.00]
Given that this is a BMW enthusiast site (and an E46 forum/section) with many current & former S54 owners, let me just say that by asking here, the scales are already tipped in the S54's favor.

That being said, with all my biases included, I would go S54.

Reasons below:

Your Usage & Goals - You say your goal is for weekend driving with occasional HPDE. Right off the bat, the fact that you are 1) not daily driving the car and putting loads of mileage, and 2) not using the car extensively as a competition track toy, tells me that the lighter maintenance and perceived reliability issues shouldn't hold as much weight as it would if it fell in either of the two categories (DD or extensive track use).

Heritage & Tradition - This one is more of an emotional argument than one based off of concrete facts and I'm sure you have contemplated on this thought as well. If this were a regular E30 3er, the argument would not be as strong but being that this is an E30 M3 we're talking about, the BMW M fan in me says it's only right to do the car justice with a proper M motor.
Having had seat time behind the S14 motor in the E30 M3, I differ in most of the fanboy reviews and die-hards out there because while the S14 is important in the pedigree & historical timeline of BMW M, it is definitely an antiquated engine and underpowered by modern standards. It was rev-happy for its time but its successor engines have since outclassed it in the high-rev department and have even more character in the powerband that leaves much to be desired in the S14.

The balanced choice - Naturally, that leaves newer M engines such as the Euro S50, S54, and S65 as contenders. As much as I'm a fan of the S65, the S54 is a much more natural fit IMO.
It's just closer to the time period of the E30 in terms of technology being that it's essentially just the final evolution of the Euro S50 / M50 block.
The platform is also versatile enough for change since it sounds like you might be seeking different methods of chasing more power.
Stock power & torque are plenty for the E30 chassis but the S54 also has enough aftermarket support and aftermarket R&D through the years to offer an array of choices with respect to builds. I'm going off of memory so the numbers might not be to the tee but you can go with a light to modest NA build with CSL components, full bolt-on and an alpha-N tune that will put you comfortably in the low-mid 300whp range while a more hardcore all motor NA build can net you in the high 300whp range. SC & turbo builds yield insanely high power as well, particularly turbocharged builds.

Trade-offs - Of course, there are trade-offs. The S54 is a proven platform but there are things to stay on top of. The general rule of thumb, especially since the engine is already out, is to swap out the rod bearings. Yes, rod bearing woes are a subject of debate...some say only the recalled batch were affected, some say all S54s are prone, some say it depends on maintenance & oil change intervals, some say to treat it like a maintenance item that should be performed every 90k-100k miles. Whatever the case, you will never be sorry you changed them preventatively, so I'd put that as a mandatory item.
The other thing to change out and keep an eye out is the VANOS. There are various VANOS bolt kits that offer better longevity & strength than the factory ones. It's one of those things you do for peace of mind preventatively because if the VANOS does go out, you're better off buying another LS than fixing the damage.
Next is the weight penalty. For a 'small' 3.2L, it's quite heavy. It might be an adjustment having gained the weight and being down on HP & torque compared to the LS.
And lastly is the maintenance. I have no experience with LS engines, but one would think that the relative mechanical simplicity offers a relatively headache free ownership experience. I could be wrong, but in any case, the S54 is definitely not one of those "just change the oil and it'll run til the wheels fall off" type of engines.
Oil must be changed religiously and the closer the intervals, the better...that's a given, but it cannot be stressed enough as there is a huge difference in oil change frequencies and the reliability of every single component of the S54.
Next is the valve adjustments, which is one of those annoying quirks of owning an S54. It's been a while so my numbers might be off but somewhere around every 20-30k miles, it is a mandatory item to check off. As a preventative measure, I'd get it done once before it even goes into the E30.
Other than that, there might be random things like sensors and valves, as well as radiator components that fail and/or need replacement here and there.
So in a nutshell, there's TLC involved, but if you treat it right, it should fulfill the goals that you have for your E30. The soft-point of the block is the rod bearings but the bottom-end is solid otherwise and will take anything else you throw at it.

Lastly, that sound. And wouldn't it be nice to have your E30 M3 to sound like a BMW again

"Modest" NA Build

CSL airbox, non-M E30 w/S54 but you get the idea
2011.5 E90 ///M3 | 6-Speed Manual | Slicktop | Jerez Black | Fox Red

E9x M3 Press/Media Archives Thread | S65-based Racing Engines Thread