Ideal candidate for 3.5l swap?

Nick · Post by **Nick** » Mon Dec 22, 2014 3:02 pm

Been looking through the FAQ's and searching but there is lack luster information and it is difficult to sift through.

At some point I will be doing a 3.5 swap, but would like to make sure I am picking the right donor. I would love to be able just to move over all accessories and "drop" in the motor. It seems that the 3.5 from 6-7 series from 88 and back is the go-to choice. Is this the easiest/best choice?

From what I have been reading the B34 takes the same mounts and is a direct swap, although the B35 is more power and requires different mounts (not entirely direct).

CabbageFumes · Post by **CabbageFumes** » Mon Dec 22, 2014 3:23 pm

Any b34 is a direct bolt in. Only '89 e24 and some '89 b32 will have the correct casting on the block for a direct bolt it. Anything later b35 will need some kind of adapter plate for the engine mount, because the only castings compatible with e12 are from e23/. e28 chassis era (e28 and e24 used the same chassis in the eighties. Once e34/32 era came they changed the subframe and engine block bosses). Some things need to be used to make the he easier, like e12 water pump, power steering pump, alt and the bracketry.
This info is in the FAQ.

Nick · Post by **Nick** » Mon Dec 22, 2014 3:37 pm

The data I'm looking at shows the HP/TQ for the stock B28 to be 181/180 with a compression ratio of 9.3:1. While the B34 to stand at 182/210 and compression ratio to be at 8:1. Seems like a lot of work for minimal gains in this instance, unless you were to raise the CR on the B34.

CabbageFumes · Post by **CabbageFumes** » Mon Dec 22, 2014 3:50 pm

The differences between b28 and b35 are substantial enough to justify the swap. Keep doing your homework. Better mileage, more power, smoother running. You'll agree sooner or later...

Nick · Post by **Nick** » Mon Dec 22, 2014 4:02 pm

Everywhere I am looking I am coming up with the same data. North American, not European.

CabbageFumes · Post by **CabbageFumes** » Mon Dec 22, 2014 4:05 pm

Ok so keep your b28. Case closed.

pappentl · Post by **pappentl** » Mon Dec 22, 2014 5:43 pm

I've installed an M90 from a 1980 euro 635 with 218 hp and stock L-jet in my last '81. I currently am installing an M90 with 1.0 motronic, again with 218 hp but taken from an '84 euro 735i. Find a newer motor or one of the M90's, they really transform the car.

Nick · Post by **Nick** » Mon Dec 22, 2014 9:17 pm

Have been doing some research, the M90 is very intriguing. Haven't seen this one mentioned before.

wkohler · Post by **wkohler** » Mon Dec 22, 2014 10:21 pm

The US-spec 528i had 169 hp/170 lb-ft of torque. The US models were lower compression to utilize regular fuel.

The Euro 2.8 on the other hand, that's your 181hp/180 lb-ft motor. If I had a car with one of those in it, I wouldn't swap a 3.5L in. I do have one of those (E28) and I'm not swapping a 3.5L in.

I have a car with an M90 (M535i) and it is a great motor. They're not easy to come by though. The later "dirty" M30s (9/82 on) are great too (same power), but the M90 is a different experience.

Nick · Post by **Nick** » Mon Dec 22, 2014 11:58 pm

Looks like I need to find a B34 or bore it out and put a B35 crank and pistons in.

Nick · Post by **Nick** » Tue Dec 23, 2014 12:07 am

Found a few tid bits of information tucked away here: http://www.firstfives.org/bboard/viewto ... sc&start=0

Looks like as long as I have the "bulges" on case I should be able to add the B32 crank and bore to the B32 pistons. 194 hp 210 lb·ft

Falkenberg · Post by **Falkenberg** » Wed Dec 24, 2014 3:27 am

On my car I had:
M30B28 double zenith made in 1976
M30B35 (?), a 3.5 litre engine from a 1987 735i, motronic 1.3.

- the 2.8 revs more quickly, or at least it gave me tat impression, it feels more playful.
- the 3.5 has more torque starting from low rpms. With the 3.64 diff I can run 4th gear (1:1) in town most of the time, no need to switch gears..

the 3.5 was plug and play as far as the engine mounts were concerned. I had to swap the oil pump though, and the oil pan of course. And swap clutch, add a bearing, since the engine was taken from an automatic car.

Falkenberg · Post by **Falkenberg** » Wed Dec 24, 2014 3:34 am

Yes I think you might be able to do that, if you have a 1980 M30, you should be ok.
I ended up keeping the 2.8 crank (80mm) and bore the block to 89mm so that I could use pistons from a M30B30.