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I wonder, beyond the well-covered issues assoiciated with converting an e12 528i to a 3.5, what additional issues would arise if we went to a stock s38 from, say, an e28/e34 M5? Suppose we had a donor car available so that the only possible problems should be fitment and linking things up. What challenges would arise?

It's been done more than a couple times.

Nice!!!

wkohler wrote:It's been done more than a couple times.

no doubt. but what's it take to get there?

Overall, it’s a project that will take some time, effort and an vast amount of patience.

For starters, you’ll need to address the brakes. I didn’t find a vacuum boost small enough to fit in the original position but I’ve heard the E30 iX may have been a possible solution. Your alternative is a hydraulic brake boost conversion. This opens up a slew of other issues you’ll need to take care of. The pedal assembly bracket should be adjusted to bring the larger 750 master brake cylinder closer to the firewall if you want to keep the original intake boot (into the plenum).
When you change to this brake setup, you’ll need to tackle the remainder of factory brake system as the 750 doesn’t provide the 4 lines to the front calipers. You can chose to fit some E34 M5 calipers and rotors (fits inside 16” wheels) but you’ll need a good machine shop to sort out the fitment if you don’t have the capabilities to perform that task yourself. If you don’t mind running larger wheels, there may be other brake options.
You can use the same transmission but I suggest a better clutch for the extra hp.
Then there’s the exhaust. You’ll need to open that up for this motor. You may also consider the M88/3 Euro M5 headers as well.
The wire harness/ECU needs to come from an E34 M5 too.
For the cooling, you should at the very least update yours with an E28 aluminum radiator. A custom radiator may be better though.
You can choose to use the E34 M5 coolant configuration or switch to an E28 M5 configuration.
A high flow electric fan will need to be installed as you won’t have room for a regular fan coming off the front of the motor.
Battery will need to be relocated into the trunk.

Then the question comes up on whether it’s worth performing such an extravagant engine swap into an E12? IMO, it all depends on what you intend to do with your car in the future.

If it’s strictly power you’re after, a TCD setup with an M30B35 would be a great alternative. Keep in mind that you should still look at upgrading the brakes as the power gain will be considerably more with boost over the stock 2.8ltr NA motor.

On a side note, an S38 powered E12 is a real joy to drive. The sounds coming from the engine compartment and out the back are truly incredible.

Two of my close friends each own a 1988 M5. They are wonderful cars and such a joy to drive. While they are both highly mechanically capable and do a great job with their cars, I am amazed at how expensive those motors are to keep on the road. From what I gather, the M30 is a much more robust and affordable motor. Just something to consider.

@Eddie: Great post. Thanks for the details. I'm sure it's a great product when it's done but seeing what all it involves I am now skeptical that it is the best way to go. I think a lot of satisfying power can be made from the M30, thereby avoiding the problems associated with fitting the s38.

I think I'll dream of putting the s38 into an e34 wagon instead. That *has* to be an easier project.



KenB

KenB wrote:@Eddie: Great post. Thanks for the details. I'm sure it's a great product when it's done but seeing what all it involves I am now skeptical that it is the best way to go. I think a lot of satisfying power can be made from the M30, thereby avoiding the problems associated with fitting the s38.

I think I'll dream of putting the s38 into an e34 wagon instead. That *has* to be an easier project.



KenB

Yes, it did have its challenges and it certainly tested my patience to new levels but the outcome was well worth it for me.

I'd imagine an S38 would be much easier to swap into an E34.

As Blaise already mentioned, an M30 is very robust and you can't go wrong with that option.