E30 Front Subframe Differences

[nnovack]

While swapping the subframe on my E30, I noticed that there are a couple differences between the old one and the new one. I wasn't able to find anything about this online, so I decided to quickly write a post to document them. I swapped an early-model 325i subframe into my late-model 318i. If anybody has more information on whether this is a difference between early/late models or between the two engines, please feel free to add. Also, if there are any more differences that I missed, this would be a good place to document them.

The main difference is in the engine mount hole/slot. On each side, there's a hole for the stud and a slot for a small alignment pin. The spacing between the stud and the slot is larger on the early-model 325i subframe than the late-model 318i subframe. This became an issue because my engine mounts would not fit in the new subframe, but this was easily solved by a Dremel. I assume most people upgrade to poly engine mounts, which eliminate this problem (most poly mounts that I've found do not have the alignment pin), but this could be useful for anybody who sticks with the stock mounts.

The second difference is the presence of additional holes on the bottom of the subframe. The late-model 318i subframe has a hole and a rounded rectangular slot on either end, slightly outboard of the steering rack mounts, as well as some holes slightly inboard of those. These are not present on the early-model 325i subframe. Considering nothing was mounted to these holes, it was not an issue, but it is something I noticed. If anybody has any information on these and what they were used for (maybe to mount a skidplate), please share.

Subframe 1: Late-Model 318i (M42)
Engine Mount Spacing (min distance): 6.75 mm
Additional Holes: Yes

Subframe 2: Early-Model 325i (M20)
Engine Mount Spacing (min distance): 9.5 mm
Additional Holes: No

Hopefully this information becomes useful for somebody. If this has already been discussed and I'm just bad at using the search function, I apologize.

M42_Mount_on_Early_325i_Subframe.jpg

MountSpacing_M42.jpg

MountSpacing_Late_318i.jpg

MountSpacing_Early_325i.jpg

FrontSubframe_Late_318i.jpg

[superj]

i think its because of the m20 versus m42 engine. there are different sub-frames but I don't know what makes up the differences other than which engine (6 versus either 4) and also awd versus rwd.

I actually just read something about this Friday, I think, while researching being able to use a different trans if unable to find a good getrag. I also learned that miata guys use our getrag 260 in their high power builds so not only are we competing with other bmw models for transmissions, we are also competing with other manufacturer people.

but for sub-frames, yes, I think there are 3 or 4 versions

[richardodn]

AWD version is it's own animal and shares nothing with the others. AWD is cast aluminum and is designed to support the revised front end geometry.