M30B35 Swap FAQ

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Brad D.
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M30B35 Swap FAQ

Post by Brad D. »

M30B35 Swap FAQ
By: Bradley Denton
Last Revision 3/05/2009



What is the M30B35?

The M30B35 is BMW’s designation for the final iteration of the M30 series of engines. It displaces 3430cc, has a compression ratio of 9:1. It was delivered in late production 87-89 e24 635CSis, all 1988-92 e32 735i(l)s and all 1988-93 e34 535is. The engine was rated at 208hp @ 5700rpm and 225 ft-lb @ 4000 rpm. The b35 can be distinguished by its valve cover with the text "BMW" instead of the Roundel on the b34 valve cover. Also, the intake manifold has "3.5" cast on the plenum instead of "3.2/3.4" on the previous models.

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The b35 shown in an e34.

Why would I want a “B35” in my car?

The stock engine in the e28 is the M30B34 which has an 8:1 compression ratio and makes 182hp @ 5400 rpm and 208 ft-lb @ 4000 rpm. The b35 obviously makes more power and has a smoother torque curve. The b35 has a more aggressive cam (264 deg duration) than the b34 (260 deg duration) and slightly more lift as well as having 1mm larger intake valves. The intake manifold also has larger runners with a different port shape at the head giving better line of sight at the back of the intake valve. The combustion chamber size was also increased to 65cc, up from 58cc on the b34. Since the b35 has a higher compression ratio, the pistons are different from the b34 creating better combustion characteristics.
One of the biggest differences though was the introduction of Motronic 1.3 DME (Digital Motor Electronics) which allowed much better control of the engine. If the b35 swap is to be considered, the wiring conversion should be considered mandatory. I have personally run a b35 off of b34 Motronic 1.0 DME and the results were less than impressive.
The electronics will make your e28 run so much smoother in all aspects of operation. Also, gains from chipping the DME are much greater than what is seen from a b34 DME. Additionally, fuel economy should improve as well.

I want to do the swap, what parts do I need?

Obviously, you need an M30B35 engine out of one of the cars listed above. However, it should be noted that certain b35 blocks have different motor mount bosses making some engines not a direct bolt in, requiring a right side motor mount adapter. All e24 blocks will work and are a direct drop in. It is reported that early e32 blocks have the correct mounting bosses for the e28 engine mount. Late e32 and all e34 blocks will require an adapter. Here are some pictures that OriginalMJG provided of his late b35 block. You can clearly see the different bosses. You can see that two of the e28 bosses are missing.
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And a shot of the left hand side of the engine.
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Koala Motorsport sells an adapter that allows the e28 mount to bolt on.
The e28 exhaust manifolds are also different. The collector flange is different as is the ID of the collector. You can bolt the e28 b34 manifolds to your b35 and it will bolt up to your stock exhaust, but you may sacrifice a small amount of performance due to their slightly more restrictive nature. The difference can be seen below. The e28 b34 manifold is shown on the left and the b35 on the right.

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(Picture c/o RobertRO)
Port size can be see here.
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(Picture c/o louielouie)

The final consideration is wiring. This will be covered in the following section.

How do I wire up my new B35?

There are several ways of tackling the wiring of your new b35. One method is to use the 1988 528e “super eta” harness. The super eta utilized Motronic 1.1 which is closely related to 1.3. It has the same 55 pin DME connector and will plug into the e28 fuse box with no splicing. I have not performed the super eta harness swap and am relaying information gathered from mye28.com on what needs to be done to make it work. There are a few circuits that need to have their wires lengthened as they are now in the wrong place to work with the m30b35. Matt (Bimmerguy2002) has reported that he needed to lengthen the oil pressure switch wiring about 1 ft. Also, the AFM, TPS IACV and O2 sensor wires need to be lengthened about 2 feet. It would be best to confirm the exact amount that needs to be lengthened once your harness is laid in place.

The second method involves using an e34 harness. I prefer the e34 harness as no wires need to be lengthened and the harness has the more aesthetically pleasing wiring loom cover over the fuel injectors. The downside to this harness is that it will not plug directly into the e28 fuse box (C101) and does not have the correct connection under the dash for the tach and fuel rate input (C103). I have compiled a wiring guide based on Rob Anderson’s original work. There are also a few other points that should be noted when using this harness. Make sure the harness is NOT from a car with EML (BMW speak for traction control). The EML car will have an electronic throttle. Another point of note is that DME pins 40 and 41 need to be tied in with the compressor “on” signal from the AC switch. Also, the b35 will have a two pin gauge coolant temp sender plug. The pins on the plug at the sender need to be de-pinned and switched. This will allow the gauge in the cluster to work properly.
Shown below is the correct wiring configuration for the C101 plug as well as a graphical pinout of C101.

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As always, all of my FAQs are intended to help the e28 community and I strive to have my information be correct. If anyone finds any errors or has suggestions or comments please feel free to contact me.
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Post by pldlnr »

Great write-up, Brad. Thanks,

Paul
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Post by rlomba8204 »

Brad-
What about using a harness from the late run e24s that use the b35? I would think there would be a decent shot that it would be long enough, and it would have the right fuse box and underdash connections. Maybe not. Or is the issue with the e24 b35 harness finding one?
Thx.
Ray
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Post by ElGuappo »

Terrific write up brad.
Brad D.
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Post by Brad D. »

rlomba8204 wrote:Brad-
What about using a harness from the late run e24s that use the b35? I would think there would be a decent shot that it would be long enough, and it would have the right fuse box and underdash connections. Maybe not. Or is the issue with the e24 b35 harness finding one?
Thx.
Ray
Ray, the e24 harness will work but it has the same canon style C101 connector as the e34, requiring the same wiring as listed above for the e34 harness, however I believe that it does have the correct C103 connector. I should have pointed out though that there is plenty of harness length to mount the DME in the glovebox using the e34 harness.
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Post by rlomba8204 »

Big Bronze Rim wrote:
rlomba8204 wrote:Brad-
What about using a harness from the late run e24s that use the b35? I would think there would be a decent shot that it would be long enough, and it would have the right fuse box and underdash connections. Maybe not. Or is the issue with the e24 b35 harness finding one?
Thx.
Ray
Ray, the e24 harness will work but it has the same canon style C101 connector as the e34, requiring the same wiring as listed above for the e34 harness, however I believe that it does have the correct C103 connector. I should have pointed out though that there is plenty of harness length to mount the DME in the glovebox using the e34 harness.
First off, I failed to mention great write-up. Thank you.

Ok, so if I understand you correctly, the e24 b35 harness will save you some time because it has the right C103 plug for the dash connectors. However, you will still need to modify it for C101, as you explained.

Also, I think I missed the relevance of the last sentence of your statement with respect the harness length. Could you elaborate? Thanks.
R-
Brad D.
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Post by Brad D. »

Regarding the harness length - at one time it was believed that the e34 harness did not have enough length for the ECU connector to reach into the glove box and that all of the wires would need to be lengthened. The thought was that only the e24 harness was practical to use, however, it has been proven on multiple occasions that there is plenty of length in the e34 harness and works just fine after the mods listed above.
The C103 connection is very simple so I don't know how much time would be saved, but it would be a bit easier. The only issue is that e34 harness are much more common than both e24 and super eta harnesses.
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Post by SD45T-2 »

good job! thanks
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Post by ismellfish2 »

Nice writeup, I wish you'd done this before I did the swap! Couple things that might be worth adding:

The B35 oil pan will not clear the e28 subframe. You need to swap in the B34 oil pan, and since the oil pump pickups are specific to the pan, they need to be swapped as well. The oil pumps are interchangable, so the lower mileage one can be used.

The coolant flow to the heater core is routed differently on the B35 relative to the B34. The B34 uses a gooseneck from the back of the head, wheras the B35 utilizes a coolant hose that extends from the upper radiator hose back to the heater core on the firewall. If you wish to use the B34 method (the flow of coolant through the head may be superior), it is far easier to remove the cover plate and bolt up the gooseneck with the engine out of the car.

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B34 gooseneck

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Removed

The backside of the flywheel (the side towards the front of the car) is covered by a bolt-on curved plate on the B34, which may not fit the B35. On an e34 the oil pan meets the transmission underneath and so there are no holes in the block to bolt on the plate.

I'll chip in some more pictures as well:

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My low-skill solution to adapting the B35 mounting bosses to the B34 mount

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Oxygen sensor plugs- B35 on right. It's a 4 wire sensor, the B34's was 3 wire. I forget how I ended up splicing those, maybe someone else could chime in on that.

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B35 valve cover, painted.
Brad D.
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Post by Brad D. »

Excellent info, I can't believe I forgot about the water neck and the oil pan. I'm glad that it is all here and well documented with pics. I am one of the believers that the lack water passage on the back of the head on the b35 in the e32 and e34 is what potentially leads to the more frequent HG problems found on those two cars due to the change in the way the coolant flowed through the head.
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Post by rlomba8204 »

ismellfish2 wrote: . . . .The backside of the flywheel (the side towards the front of the car) is covered by a bolt-on curved plate on the B34, which may not fit the B35. On an e34 the oil pan meets the transmission underneath and so there are no holes in the block to bolt on the plate.
So maybe I am missing something (probably I am), but what is the solution to this issue?
Brad D.
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Post by Brad D. »

I do know that on my late e24 b35 the curved aluminum cover bolts on just fine. I am not sure how the e32/34 b35 users are attacking the problem.
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Post by DaRedRocket »

Great write-up Brad :up:
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Post by ldsbeaker »

Outstanding, thank you!!

Am I correct in assuming that all of the other B34 accessories switch over? AFM, etc?
... and most people use a specific DME for their B35, right?
(the number is escaping me now, I want to say 179?)
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Post by ismellfish2 »

rlomba8204 wrote:
ismellfish2 wrote: . . . .The backside of the flywheel (the side towards the front of the car) is covered by a bolt-on curved plate on the B34, which may not fit the B35. On an e34 the oil pan meets the transmission underneath and so there are no holes in the block to bolt on the plate.
So maybe I am missing something (probably I am), but what is the solution to this issue?
My flywheel is still exposed- I haven't gotten around to figuring it out.

Regarding the DME, either Motronic 1.2 (150 ECU) or 1.3 (179) can be used. 1.3 is presumably better.
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Engine swap m30b35

Post by edlocke »

Thanks guys, great info! It sure makes life a lot easier having this info.
As far as the power goes can you tell a noticeable difference?
Can you use the b35 tranny with the swap? would drive line and linkage bolt up without any problems? I'm just thinking about the exposed flywheel issue.
One other question, does the b35 head have the water return capped off or is it just not designed into the back of the head like the b34?
thanks guys!
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Re: Engine swap m30b35

Post by Shawn D. »

edlocke wrote:One other question, does the b35 head have the water return capped off or is it just not designed into the back of the head like the b34?
Kinda neither. The B35 head has the exact same outlet hole/flange as the B34, but it has a blockoff plate in place of the water outlet. It's a very simple R&R situation.
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flywheel exposed

Post by edlocke »

So I take it to cover the flywheel one would have to fabricate a cover?
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Re: flywheel exposed

Post by Shawn D. »

edlocke wrote:So I take it to cover the flywheel one would have to fabricate a cover?
Yes, if you are not using the E24 B35 block/pan/cover.
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Post by Bimmerguy2002 »

You wont have an exposed flywheel if you use the m30b35 oil pan :roll:
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Post by Shawn D. »

Bimmerguy2002 wrote:You wont have an exposed flywheel if you use the m30b35 oil pan :roll:
Roll at yourself, Matt. There's no "the" M30B35 oil pan, but an E24 B35 pan and an E32/34 B35 pan. Only the former will work in our chassis.
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Post by Bimmerguy2002 »

Im using the E32 pan, fits fine, and fits better than the b34 pan, and it sits higher too! I actually did the swap myself just to confirm it, if it doesnt fit, then i somehow dont have a b35 swap in my car :shock:

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Post by ldsbeaker »

THANK YOU.

For posting something and then showing pictures and proof.
edlocke
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engine swap

Post by edlocke »

This boards great. Where else in time could you have the knowledge and expertise that we have on this board. thanks guys.
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Power steering pump

Post by SamSpade »

Excellent info as usual.

I'm currently swapping in a M30B35 into an E23 728i. Most of the concerns were addressed in the posts above.

How about the power steering pump? The B35 I got included a PS pump. Would it be better to use that or the old one? Do they operate on the same flow and pressure ratings?
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