e28 owner with stroker dreams

[divingboardlord]

Hello everyone,

I have a 7/85 build date e28 528e that I nearly have a complete manual swap for, and I have began thinking about what I would like to do with the car in the engine department. I'm well aware that slapping head studs and a turbo on an m20 or m30 will get me well over 300hp with the right kind of setup, but something about all the options there are to make improvements to the m20 engine using a lot of OEM parts seems really fun and appealing to me. On top of that nothing quite beats the sound of a naturally aspirated engine to me, and nothing beats that nice, deep idle sound that single cam BMWs have. Additionally, all of the m20 parts I've collected and already have on the car kind of lock me into using an m20. I've developed a loose plan for what I'd like to do, and I'm hoping to receive some feedback as far as how much it makes sense to some of you who have done something similar before. The plan is as follows:

1. Find a decent running m20b25, re-seal the engine, replace the water pump with one compatible with my cooling system, and get the head refreshed and possibly ported and polished.
2. Swap the m20b25 into the car using my super eta harness, and get it running reliably on the factory m20b25 ECU.
3. Figure out what the ideal exhaust setup would be.
4. Purchase a standalone ECU, likely a pnp megasquirt, and once again get it sorted out.
5. Purchase a Schrick 284 cam and heavier valve springs, and get them installed, with heavy duty rockers if necessary.
6. Get the car tuned to account for the modifications.
7. Strip down the m20b27 block that was removed from the car, purchase 10.5:1 CR pistons custom made for a stock eta bottom end, and have the engine rebuilt.
8. Remove the m20b25 once again, and reassemble the engine with the built eta block installed.
9. Re-tune for further modifications.

I know that this kind of setup won't produce ridiculous power numbers, and I know it won't be cheap, but I'm confident that I can do a lot of this work myself, and I already adore driving the car pushing 120hp through an automatic transmission with a 2.93 LSD, so I'm sure this setup will never fail to put a smile on my face. I'd like to think I've done my research, but because this is my first car (not my daily anymore) and I've never really done anything like this before, I want some second opinions about what I'd like to do and what issues I may run into when doing them in this order. I also have some questions I've never really gotten answers to when lurking in other threads. I'm aware that three of most restrictive areas in an NA m20 are going to be the head, cam, and intake, and this plan fails to address the intake. Seeing that ITBs are expensive and not ideal for a street car, what can realistically be done to the factory intake to make a considerable improvement? I've seen that SSSquid tuning has a throttle body spacer that claims to improve the factory intake, for $80, would this be a worthwhile addition to my list? It seems as though the only companies that make headers for m20 powered e28s are OBX and supersprint and the OBX ones aren't liable to make any improvements, the supersprint ones are $$$$$. Do I need to worry about this, or would a certain factory set of M20 exhaust manifolds do me just fine with this kind of setup on a street car? I've heard of using an s52 crank with a b25 block to produce a similar result to this, is there any benefit to that over my plan considering I'm going to have an eta block and rotating assembly ready to go after the b25 swap?

I'd really appreciate some constructive criticism on this, and I love talking about this stuff, so I look forward to hearing from you guys.

Thank you for reading,
Roby

[AWDBOB]

E28 doesn't give me stroker m20 vibes, it gives me m30 vibes. IMO a stock bottom end b35 with a head shave, 272 cam and lightweight flywheel would be my course of action.

You can get a flywheel from RHD that uses a 228mm clutch so a lot of your manual swap would still be compatible.

You can still use your SETA harness to run the m30 as well. Probably same power as your end goal, with more torque to move around the 5 series, done in one go instead of in several iterations.

[digger]

The e28 came with M30 from the factory, as stated above that's what id do it. A m30 with a bump in CR, proper tune/ECU, mild cam, nice set of headers will be a nice thing.


if you still want an m20 and are prepared for custom pistons you wouldn't use the eta crank you would use the m52b28 crank as a minimum. For more torque, seeing as it is an e28 the better option is a larger displacement M30 rather than an S52 based m20 as the larger M20 with the stock head and intake will be choked badly and takes a fair bit of effort to get it to be better than a M30 which starts out with bigger everything

[divingboardlord]

Thank you for your input! I still really love the idea of doing an m20 stroker build, maybe I'll have an e30 one day, and then that would be the time for it. I tend to underestimate m30s because of the sad compression ratio the US m30b34 was given. That being said, I just got an 85 635csi a few months ago that I am not opposed to swapping an m30b35 into, so perhaps I can do a more involved build with that and see if the manual swap, a shorter diff ratio, and a chip would wake the e28 up enough for me. I daily drive a 2008 Cobalt so maybe even the heavy e24 with be "kind of fast" by my own standards, so we will see! Thanks again!

[AWDBOB]

OP, I have an m30b35 and g260/6 up in Indy that I've been saving for an M30 swap, that I could be convinced to sell. If interested, send me a PM.