M52B28 to S50B32

[Jimb03]

First time posting, I have a potential project I'm researching.

Candidate is a '97 328is with an M52B28.

Desired end result is an engine close to the Euro facelift S50B32 in both displacement and power (obv will not be unhappy if either is greater than the target)

I can get an S50B32 crank which has a stroke of 91 but that's an expensive option. I'm 99% sure the B32 crank will fit without issue but I want to see if anyone knows if there's a problem I'm unaware of. Engine will likely be bored to 86.4 to accommodate upgraded S52 pistons. With a compression ratio of 11.5:1 this would yield an exact 1:1 displacement copy. The real question though, is can the same or more be achieved for cheaper. The bore isn't too much of a concern, 87 mm would be nice but most of the power comes from the stroke. I don't want to use a 97 mm stroker kit because that'd yield an engine a little too extreme for my liking (3.4L). So I need to know if there's a cheaper way to get a stroke close to 91, but no lower. B32 crank would cost about 2k all told so that's the target. The engine would have plenty of supporting upgrades, cams, exhaust, injectors, manifold (potentially ITB's since I believe the B32 came with those), and a double vanos install (I have a couple ways of doing that but I'll settle on it later). Objective in the way of power is 320+ at the crank (same or more than stock S50B32).

Lmk what's out there I'm getting brain fatigue from all the stuff I've figured out in the last two hours or so lol.

[MauiM3Mania]

The parts shared by the US S52 and the S50B32 are few. Oil filter, a few external bits, i.e., motor mounts, alternator (maybe), bolts, etc.

Get a S54.

[pbonsalb]

The USA M52 and S52 have been around for 25 years. Plenty of people have spent more than 2 hours trying to figure out if it is possible to get 320 hp out of the motor, whether expensively or inexpensively. My take, after reading about these efforts over the past 18 years, is that it is not really possible for a street motor that is expected to have a long life. There is a good, fairly recent thread by Aeronaut in the Track subforum that is worth a read.

I like the S54 recommendation. Back when used S54 were $5k, some DIYers were doing the conversion for under $10k. Might be more today since S54 prices are up.

Supercharged S52 or turbocharged M52 or S52 are also worth exploring. I have had both on my S52. I have also fully built an S52 out of an M52 block and can say that a really nicely done head will cost twice that of the built block. Mine has modest cams for forced induction and I use a redline of only 7200, but for big NA power, you need much more aggressive cams and a higher redline.

Good luck and report on your journey.

[Jimb03]

A little view of the greater project:

The car will be receiving the E46 420G transmission first. I'm looking to create an EVO style car with a similar engine. The car is an auto which makes the 420G swap easier since I can reuse the driveline. An S54 swap is absolutely on the table. I'm weighing that against the possibility of building the current M52B28 block, and also the very distant possibility of importing an S50B32. If I get an S54 the engine will be rebuilt anyway (I'm not going to trust a used 140k S54 without replacing the rod bearings etc.) so the labor isn't much different between the three projects. I'm just looking for more information on NA M52 builds to see if it can compete with an S54 swap by undercutting the price of an S54. The transmission swap will, hopefully, be happening in the next two months or so but the engine swap / conversion is a ways down the road.

Edit: I just realized that I can kill two birds with one stone by buying an E46 M3 if I can get one on the cheap and just rip the drivetrain. It'd be a little awkward with my space situation but not impossible. I might just go with this approach if I can find a trashed E46 M3.