BMW 3.0CS - M5 Motor Conversion



Howdy and welcome. I originally responded in the other thread.

I am starting with a 91 M5 and a 1985 535i as donor cars. Using the S38B36 from the
E34 M5 and the Getrag 265 from theE28 85 535i and if need be several other parts.
Great swap!
Make sure you reinforce the frame of the car or you risk serious
body flex from the much higher than usual horsepower.
There are a number of
threads on this, and coupeking's website shows some of the reinforcements the factory
racing teams used back in the day.

I am having an issue with the hood shutting as the inner hood reinforcement rod is
hitting the fuel rail of the S38. Do I need to drop the engine cradle a bit by means of
shimming? or do I need to use different motor mounts and brackets? or simply cut off
the rod. I had the same problem, and removed the hood support. Right now I'm kind of
puzzling over it, but it certainly won't end up being the same system that most CS/CSi's
run. (Right now, I run with a race hood prop in the trunk for emergencies.)

I'm concerned about lowering the cross-member as that places the oil pan closer to the
ground. I used the E28 535I center tie rod link as the original one from the coupe did
not clear the S38B36 oil pan. The oil pan is also in the way of the sway bar. Have to
figure something else for that. Read on this forum where someone used the oil pan and
the oil pump from a 79 528i to solve the clearance issues with the sway bar.(is this the
only route?).  I've heard this before but we didn't have that particular problem . Did you
upgrade the engine mounts?

In order for the rather large S38B36 intake plenum to fit
I will be installing a hydro
boost brake set up from a 79 BMW E23 733I which some prefer over the E28
535I hydro boost as the later is longer by and inch or two. Converting to a
1974 2002 tii booster as few have suggested is not working for me.  Hydro
boost from the M1 also fits and is surprisingly not that expensive!

I will be adapting to use the bigger diff and boxed trailing arms from the 535i. The
original C channel built E9 trailing arms seem too flimsy to me to handle the extra
torque of the S38(of course the body will be reinforced as well).  I used an original
3.45LSD and haven't had any problems yet. I thought of going your way and decided
since there have been cars running 500+hp on side loaders upgrading was not
necessary. But that's not a knock against your proposed approach.

Must I use an electric fan for cooling? I prefer to retain the fan blade and clutch set up
for cooling. To achieve this do I need to move the radiator support forward? Which
BMW radiator should I use? Any engine oil cooler placement and fitment suggestions?
Any AC upgrade suggestions as my coupe was not equipped with AC?  This is a big
question. Since these cars are all just a little different, you might have enough room to
go with the mechanical fan. We had enough room, but then decided to switch to a
modern style radiator, which led like falling dominoes to an electrically switched fan.
There were some minor modifications that had to be made to the supports, which will
be obvious when you get there.

Re AC, your toughest job will be to source the parts that go inside the car. We had to
get a blower from Portugal! Once you have everything inside the cabin, there are a
number of options. My approach was to use modern parts in front of the firewall, and
the 5-series compressor that works with the S38.   

Where is the best place to house the S38B36 engine computer?  How much of a
restore are you doing? Lots of folks go glovebox, we went inside the heat shielding in
the passenger floorboard (in a protective box).
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I put in a 3.5 from a 91 535i complete with the Motronic. I can dig up my wiring digram
(it will be almost identical.) I am not sure about the S38, but all M30 engines after 89
were missing a couple mounting bosses for the passenger side of the engine block
which necessitates fabrication of a custom engine mount bracket. Also, the bell housing
may be different, so manual trans only. I know that the E12 has the same dimensions
as the E28 where it counts for driveshaft placement, so you may get very lucky if you
can get an E28 M5 driveshaft. I never got around to conversion of mine to a manual
before I sold it. You must fabricate a clever cable throttle because the CS has a linkage
throttle (but I can give you tips on that, having done it for my family's old E12 530i auto
to E28 motronic manual swap.) You will probably have to change the brake booster.
You may need to go hydraulic boost to get it to work, which means you need an
E23/24/28 parts car with working boost stuff (easy to do.) If you have any questions,
just let me know. I love motor swaps and think they are "easy" but that does not mean
they are fast or require no thinking or custom fabrication. Also, your temp gauge will go
nuts because it will think your car is always overheating. I never did install a resistor,
but that is all it would take to fix that issue. You need to install a fuel pump assembly.
You can go in tank, ot pull the pump/filter cluster from an E28 or similar and bolt it
under the car, which I did. I made a custom pickup that went into the tank and used the
existing feed line for the return, running a new steel line under the car for high
pressure to the fuel rail. If you really feel like it, you can even install an E28 rear
subframe and diff. Use a trans with speedo gear definitely. Otherwise you need to do
lots of wiring for an electronic speedo. I suggest a Getrag 265 gearbox from a 528i
(1981?, I think.)
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We had a whole M5 wreck. My advice is that the more M5 parts you have, the easier
the project. Key to the conversion is using the front and rear subframes from the M5 so
that the suspension, steering, ABS brakes, and engine mounts are there. Everything
lines up, and the bolt sizes and patterns are the same between CS and M5. No sheet
metal fabrication work was required except cutting off the front frame rail pads for the
old subframe. It is also probably wise to reinforce the differential mount by boxing in
between the rear frame rails.
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