N52 Swap Discussion

[LukeJ]

That's a cool idea. Surely, easier than fabbing an entire mount! But it does require you have a machine shop and some skill. :p

Yeah, Thanks !! It's about time I use these skills to make something for myself for a change.

Still won't know if it's a good idea until I put the engine in the car. Maybe the fabbed mounts will be the better way to go?

[hubcapboy]

I love where this is going.

Has your subframe arrived yet? The pads that the motor mounts sit on are sloped in. So the taller mounts will also be closer together.

Mine are EVEN taller... because they’re sitting on those 1/4” spacers.

If you retain the m20 mounts and have extra height to spare, your collar could make up the difference if you added a flange and stud to bolt to the original hole?

i tried to draw it with my 2-year-old’s crayons just now and it doesn’t make it any clearer lololol

[hubcapboy]

If the offset is only that much you could probably cast your own urethane mounts. The machine work to create the inserts would be trivial.

Offset the top and bottom by an inch, retain the complete z4 arm and no need to modify the subframe.

[LukeJ]

Yes, my subframe did arrive. That's how I was able to determine that I'll be going with a front sump oil pan. ;-)

[LukeJ]

The pads that the motor mounts sit on are sloped in. So the taller mounts will also be closer together.

Another thing that I found and thought was interesting is the difference in angles when comparing motor mount arms and subframe mount locations. The E85 mount arms had a 15 degree angle sloping/tilting toward the center. The E30 front subframe mount locations are 20 degrees. I figured they would be the same. I don't know if the M20 mount arms share the 15 degree angle or the 20. I'll probably try to measure it once I get the M20 out of the engine bay.

[hoveringuy]

Or even if the e36 mount arms are 15 or 20 degrees?

[nando]

all 24v motors have the same angle relative to the chassis (is it 20 or 30 degrees? I don't remember - I think 20?). But that doesn't mean the angle on the subframes are the same, although I think they'd be?

[hubcapboy]

The tilt from vertical on the m20 is 20 degrees, the tilt on all 24v engines is 30 degrees. This allows for more room for the more complicated cylinder head.

the angle we’re looking at right now is unrelated to that... on all of these cars the motor mounts (rubber part, not the arm) are tilted to the interior at the top.

[hubcapboy]

OK... I know I said no more AC updates, but this might be the AC solution... so I might get away with it. I haven't worked on the car for a week because of a trip and work, and now it's raining, but I did get out to pull the tarp off the engine two nights ago and I think this is worth sharing.

I'm and engineer, but not an electrical engineer. I DO have pretty consistent contact with two pretty savvy practical hardware design electrical engineers both with an interest in this project. We were ready to design a PWM controller for the n52 with off, low, medium, high output settings that pulled a "safe to operate" signal from the e30's AC controls (pressure switches, evaporator temperature, dash buttons, defrost lockout) and then sent a soft-start output signal to the compressor that picked an output from engine RPM (higher RPM requires less output). I have a few PWM controllers lined up on the bench, I pulled out my variable DC power supply... and then this arrived in the mail:



The top is the N52 compressor I pulled off (you can see my AC Comp label on the plug I snipped from the harness to start poking at it). The bottom is the compressor from a BMW M73. I didn't know that engine code off the top of my head, so don't be shy if you didn't. It's the V12 from the 7 and 8 series from 1994-2001. In other peoples underhood photos from those cars, it looked suspiciously similar, but as far as I can tell is a conventional clutch operated compressor (confirmed via the 8 series ETM, the fact that the wires go to the front instead of the back, and sheesh it's from 1993). I started this search by looking at serpentine belts. Most BMW compressors are driven off a secondary belt (which is why they're so easy to delete) which has a narrower width and fewer grooves on the pulley. For whatever reason the M73 is driven off the main belt like ours, and had the same number of grooves. They were both Denso OEM, and I figured if they looked this similar there was a decent chance that the bolt faces and pulley location were the same. All of the compressors from this era look like they use a bracket to adapt to the block:



Which made me think they were using some Denso standard for the mounting. The N54 has aluminum inserts directly in the mag block that the compressor bolts to. I looked for junkyard compressors to check fit, but as soon as I realized that a new M73 compressor was half the price of a new N52 compressor OR an original e30 compressor, I just bought a new one (and figured if it didn't fit I'd just return it. Here's the back-side of the two compressors:



The housings are so similar that I find it hard to believe the internals are different... but... I'm not going to second guess that. I offered the compressor up to the block and it "fooped" right onto the aluminum bosses... exactly the same pattern and diameter. I was so surprised I didn't even measure the pulley diameters. The new one looks a little smaller and might be under-driven at idle, but this is probably helpful for a higher revving engine (ok ok ok... stop PMing me... smaller is overdriven. helpful for... not having to raise the idle when the AC comes on. how 'bout that). There's enough movement in the tensioner to make up the difference if there is one:



I better check if it clears my radiator...

[nando]

That's awesome, and makes wiring so simple (just use E30 wiring!). I'll bet you can swap out that pulley too if it's interfering with the radiator.

I'm sure you already know this, but just make sure you use aluminum bolts instead of the steel ones that probably came with that compressor. Was it remanufactured? it looks brand new.

[hubcapboy]

Maybe the fakes are getting this good, but this looks like a new production japanese made Denso. Their part number for it is 471-1262, and I expected it would pop up in a bunch of different applications based off that number... but it doesn't seem to. I'm sure this is some kind of internal code they use like a 471 pulley is a certain belt width, certain diameter, and the case is a 1262 which is a certain type of pump, certain pattern, and certain output, but I haven't been able to read those tea leaves.

It's such a low volume part I can't imagine there's fakes tooled up (on the other end of the scale, it's almost impossible to find a real Denso gear reduction starter for a Ford 7.3L diesel...) The packaging is also labelled "no core value" so these may not be rebuildable.

[hubcapboy]

Work has been... an obstacle. No meaningful oil management progress to report. In the meantime, I’m stressing out about the alternator:

https://bimmerprofs.com/alternator-management-problems/

anyone with any insight... I’d appreciate your thoughts. It seems that in cases where the alternator is mismatched with the DME (like, say, if we flash the DME to make it think it’s a Z4) the alternator may refuse to do any of the active management that the serial connection allows. Even if those two components are willing to communicate, the loss of the battery module may cause the DME to tell the alternator to go to failsafe anyway.

I’m not sure how to reconcile this with the success stories except to wonder if the failsafe is “good enough” for our uses, or if the constant output reduces life of the alternator meaningfully, or if it’s even worth connecting the alternator to the dme.

I have a feeling this is going to start a hunt for a similar solution to the AC... “is there an alternator that bolts up that just has a voltage regulator.”

[nando]

Afaik, failsafe just runs it like a regular alternator. Although I don't see why the IBS wouldn't work. But, this has never been a problem.

[hubcapboy]

Do we know that these alternators are talking and being controlled by the DME?

I guess my question is unless we know what functions we’re getting out of the BSD... why connect it? Just let the alternator run conventionally?

[nando]

Yes, the DME controls them.

Well, it's more efficient with the IBS sensor - it only charges the battery as needed (reducing drag from the alternator), and theoretically extends the life of the battery by adjusting the charge profile as it ages, and fitting it closer to the actual size of the battery as well (which is why you register the battery size & type on new cars).

But whether this difference is enough for you to be bothered - I don't know. and certainly, an E30 has much simpler electronics and is much easier on the battery overall than say, a fully loaded X5..