Original engine or M30B35 replacement

[thehackmechanic]

As others have said, it really is a question of whether you want a largely original car or are open to upgrades.

My E9 is a CSi whose D-Jetronic was removed before I bought it. Under my ownership, it got an M30B32 engine with an L-Jetronic injection system from a 1980 528i. This is not as modern or as good as the M30B35 and full Motronic 1.3 system from, say, a 1990 E34 535i, but even my system starts instantly in cold weather, idles smoothly, and delivers power in a way that's far superior to the dual Webers on my Bavaria. If I came across a full M30B35 drivetrain with everything intact at a fire-sale price, I'd snap it up and drop it in the car. Of course, the originality ship has long sailed on my car (color-changed, interior-swapped, on and on).

IMHO the main downside of the drivetrain modernization other than lack of originality is that a) the Motronic intake manifold has a very different look and feel when you open the hood, and b) you have to deal with the fact that the Motronic intake manifold won't clear the brake booster (if I'm wrong about this, folks please correct me). People deal with both of these by using the old "brontosaurus rib"-style intake L-Jet or D-Jet intake manifold coupled with a Motronic fuel rail. You also can install the hydraulic "brake bomb" in place of the booster.

 

[sfdon]

Correct Rob- the idea is to look like a Csi Djet and run like a Motronic….

 

[lip277]

Related to this question was the process I used when figuring out what to do for addressing my old engines woes...
I liked carbs. Had a Weber 32/36DGAV on my 2002 for many years. Then upgraded to a 38DGAS. That was even better....
I may have been lucky - but I never had any issue with the carbs I ran. Once they were set- they worked great for me. But I knew having two carbs on the M30 (as my 2800CS had) was asking for a bit more trouble that way.
That and what I was wanting to do on the Coupe was a bit more performance oriented . From there - I was open minded on the rest.
I had wanted a CSi -but was not liking how the early Bosch EFI systems were getting harder to work on (both in terms of parts availability and finding the people who know about them). That is when I settled on going Megasquirt for my new motor. If you look at my set up - it appears to be a stock CSi. But, under the skin - is a new Megasquirt brain controlling everything. FYI - The last pic above is of my car in Don's shop (after the M90 install - with the CSi look).

SFdon did everything - but there are other folks that also have done them. Sven (up here in Seattle) also has one on his car that he did on his own. There are also other EFI systems that are out there I think that are similar - but I went with what SFDon uses - just because....