M50TUB25 Rebuild/Stroker OR S52 High Mileage Rebuild - Mix-and-match potential?

[LovelessAndroid]

Good morning, gents. For some background, I have a 1990 325ic that I've owned for 8 years. The M20 runs GREAT and the car was totally refreshed by myself ~5 years ago. I am in search of more torques, anyone have some they can lend?

Basic question... I have a good running E34 parts car with an M50TUB25 with 222k miles, so OBD 1 obviously, that I basically bought for the oil pan but was planning on using the block and head given it has the desirable intake. Should I build up that block with an M54B30 rotating assembly and intake camshaft? I like OBD 1 for ease but also because the Megasquirt3 PNP is OBD 1 based. So if I ever want to go stand-alone OBD 1 is good for that.

OR I also have a lead on an $800 (plus $200 flatbed Uhaul rental) 1998 M3 parts car with 218k miles and an automatic transmission. Should I go for that and use the S52 internals on the M50TU block? Or mix and match parts to make a good motor? OBD 1 or OBD 2? I know there's no limitations to OBD 2 really anymore if you can pay for a flash tune. I know the OBD 2 headers are good for the swap too.

What would you do in this mix-and-match situation?

IF YOU WANT THE LONG STORY, KEEP READING. OTHERWISE THANKS FOR YOUR TIME!

I have always been open to doing an ETA-based stroker and turboing, learning how to tune with Megasquirt on the way. However, as budget friendly as an N/A M20 is, turboing it and doing aftermarket ECU is expensive across the board. The more I read on M20 mods versus 24V swaps, the more I feel like a 24V swap is in line with my long-term goals for the car. So the goal here is N/A (to start), modest power goals (coming from a 190k M20 that's not hard to beat), and to build the engine myself (minus the machine work). I also like the fact that I can get a Stage 2 clutch and re-use my M20 flywheel and G260 and driveshaft, differential, etc. Not only is that budget friendly, I like the OD 5th gear on the G260 to go with my 4.10LSD I swapped in. Yes, it's weird but I plan on keeping the 4.10 because I am keeping this thing around town and my highway speed revs at 70mph are only 3400 or so. Not that bad for my 15 min drive on the highway to work. I know turbos like load, and I have no desire to spend $500 on a 3.23 LSD also.

So anyways, once I clicked with 24V swap, I started doing a ton of homework and figure out a strategy to approach it budget-friendly. First hurdle... E34 oil pan. So I randomly started looking for E34 525is... just so happens I found an entire (barely) running 1995 525i listed at $500 with 222k miles on the clock... Guy immediately said he'd take $350 AND my amazing wife agreed to let a parts car haunt our driveway... Given that I couldn't get keep it running we settled for $300 and I took care of the tow, which with tip was $100 so I am all-in $400 on basically a $250 oil pan setup attached to a parts car. I will part out some stuff like keyless entry, brake booster, check the differential, easy stuff like that, before junkyard pick up. I hope to get cost-neutral on this.

I did end up figuring out after 50 attempts at the stomp test that it had one code, the air flow meter system. Digging in, I found the crankcase breather hose fell off from being SUPER loose. A few hose clamps and I had a running car... Wow. I know people do this all the time but it felt great to buy a car for $400 all in and make it run. The interior is trashed but the exterior is rather presentable. It is an attractive car, albeit not as attractive as E39 ha.

So then I am browsing recently and I find a listing for a kid parting out a 1998 M3 sedan, automatic, with 218k miles allegedly a strong running engine... I message about if the motor is pulled and best price. Kid immediately drops to $800 saying if I bring wheels (will E34 wheels fit over the M3 brakes?... I really don't want to buy wheels just for a single sale...) I can drive it off for $800. That would give me ECU, wiring harness, motor w/all parts, and even the rear differential that I can use to part out before scrapyarding the car... Dang right?

However, I need to make the case to my wife that it's okay I went from ZERO parts cars ever, to TWO at once... Given the slow downs at work, I do have time to wrench though.

[KIRIEIW]

One thing I can tell you, don't just swap that M50 in. You'll be seriously disappointed if your expecting a significant power upgrade from a M50 swap (coming from your M20, I suppose coming from a M42 could be different).

Anyways, my vote would be to do the S52 and use all the OBD 1 parts from the e34 M50. Unfortunately you would need a e36 M50 or S50 OBD 1 engine harness rather then using the e34's M50 harness (it's a little short and might not reach the ECU mounts in the glovebox, while the e36 is the perfect length). Put the S52 on a engine stand, replace ALL the chain guides and timing chain, oil pump chain, all the gaskets, water pump/ tstat. Roughly $500 in parts for all that, not bad. Chain guides or the oil pump nut seem to be the main killer for these M5x/ S5x engines, or a cooling system failure.

Use the e34 M50 ECU, and get a chip designed for a S52 in a 413 red label ECU (the stock e34 ECU).

I think this is your best bet for a swap, it's basically a full bolt in swap and don't need to mess around with Megasquirt, ect. (unless you know how to tune and such?)

[KIRIEIW]

Also after doing 3x S50 swaps at my house in the past year-ish, I miss the M20. You might want to consider just keeping the M20 and enjoying the stock engine!


PS: I would not mess with internals/ swaping cranks, blocks, ect. All the fasteners are stretch bolts and can't be re used. Only BMW sells the bolts and aren't the cheapest at roughly $9 dollars each bolt. With that said the bearings should be fine unless a chain guide broke and partially blocked the oil pump pick up screen.

[LovelessAndroid]

Thanks for the input! Agreed on not swapping the M50 as is.

So, first off, you suggest using the M50 head with the S52 valvetrain to keep it OBD1? I know with S52 cams you need S52 springs right? Then get an OBD1 tuning chip.

Then I should use the S52 block with rotating assembly kept totally as is, unless damaged, even with the high mileage?

Why do you miss the M20? Reliability? Simplicity?

[LovelessAndroid]

Also the E34 harness I've heard a lot of people using it successfully but it is tight. It appears it may be a good candidate to modify the harness versus an adapter to cut down on the bulk.

Otherwise... I am fully mentally prepared to tear apart the bottom end. I know there's a lot of dumb fasteners but I can always go with ARP at some point.

My plan right now is to get M54B30 to stroke the M50TU, rebuild the VANOS, refresh, etc.

Then if I need to bore out the cylinders for a bad upper ridge I'll source 6 x M44B19 pistons to go 85mm and bump compression. I did a TON of spreadsheet work adding up the heights of all the rotating parts to see if the M54B30 is the absolute best. $/Liter it is for sure.

[ZekeTheSneak]

E34 harness works fine. IMHO obd1 is a waste of time in this day and age. I could never get my check engine light to turn off. I would go m52 obd2 for best bang for buck or s52.

Any experience tuning or know anyone? The plug and play megasquirt kits for the m20 add hp and better drive ability. If I were to do it all again I would have gone megasquirt, then turbo. For the stock m20.

[LovelessAndroid]

So the Megasquirt PNP kit is for OBD1 so there is a short versus long term balance here.

Agreed on the strengths of Megasquirt but also that OBD2 swaps aren't really an issue anymore.

[ZekeTheSneak]

I was referring to the m20 megasquirt kit. Sorry for the confusion