Using an 318, 328, 323, M3, or automatic transmission car to build a spec3? Read this

As always. Please consult the Spec3 rules and utilize those first as your reference for what can, can’t, and must be done in a Spec3 build. After that, please read the Spec3 Constructor’s guide, which is 90+ pages of information gathered from the 100+ people who have started Spec3 builds. If you have a question, it’s probably answered already in those two documents.

The easiest way to build a spec3 is to start with a manual 325i E36, however, since all E36 chassis sedans and coupes are the same, the items to swap to use something other than a 325i are fairly straight forward.

If you have no extreme personal attachment to your non-325i E36, we recommend you sell it and try to find a good 325i to start your build with. Typically you’ll come out ahead financially as people pay a premium for 328i and M3 cars.

If you’ve read all of this and still want to blaze ahead, then his page is for you.

To keep yourself out of trouble should you be a front running car that gets sent to impound often, keep in mind that unless stated otherwise in the rules, all parts on your car should be parts that could have come on a 93-95 325i from the factory (within reason). Luckily, late 1995 325i cars got most of the updates that the 328 and OBD2 318 cars got and that opens up the legal parts list for folks doing a Spec3 build with a 323i, 328i, m3 or late 318i. The most complicated part of using one of these cars is making the OBD2 wiring harness work with the OBD1 325i parts, but professional harness modifiers like Tulay’s Wire Werks can do all of these changes for you and they offer a Spec3 discount.

If you have questions along the way, please utilize the Spec3 discussion group where you will find plenty of people who have done these kinds of builds that can help.

We also have an unofficial “parts compatibility” spreadsheet to help determine which parts need to be swapped from a 325i donor car onto your 318/328/m3 to make it Spec3 legal. https://docs.google.com/spreadsheets/d/1HLraPTno1H5gmn34nZpJ3OOsuwaK6uo6oFadOapUBuQ/edit?gid=0#gid=0

Additional Notes for 328 to Spec3 swap from Mark Hoffman

Hi, this is a summary of my experience building a Spec3 out of a 328.  After completing the build, I would advise that it’s not the easiest/quickest/cheapest way to produce a Spec3, but can make sense under the right circumstances.  A 328-based Spec3 build works when you were already intending to do a full ground-up gut and restore job where Step 1 is strip the car down nearly to bare shell.  If that’s your vision and someone gives you a free or practically-free 328 that has a straight/clean chassis, then it’s a fine way to go.

Spec3 has a great interchangeability matrix for E36 models and what can/cannot be used for a Spec3 build.  The list is thorough and should be consulted first when evaluating what parts you will need for your build.  I did not address each non-interchangeable part below, instead addressing where I ran into weirdness or ambiguity with the conversion.

Resources that made the job achievable:

  1. A Bentley Manual

  2. Constant referencing of RealOEM for diagrams and part number/arrangement confirmation.

  3. An extremely patient community of Spec3 racers who were quick to answer all my questions via the facebook discussions.

  4. Great vendors that are quick to support their products with technical help and troubleshooting (Bimmerworld, Race German, FCP Euro, Tulay Wireworks).

  5. Access to an assembled/functional 325 (preferably a Spec3) that you can reference for arrangements, routing, etc. I spent a lot of time poking at Spec3s in the paddock and taking copious pictures of everyone’s cars from all angles, it was immensely helpful while I was putting mine together.

  6. Outsourcing the wire harness conversion to Tulay Wireworks.

Places where the 328-Based build will vary from a 325-based build:

  • Power Steering Pump + Lines (2/3)

    • The M50 oil filter housing will not accept the brackets for a 328 Power Steering Pump.  One could theoretically get creative and rig up some spacers, but it would require some fabrication and is a lot of work to install an illegal part.

    • Additionally, the M50 power steering pump fluid line attachments and lengths are different than an M52 pump, so you will need to replace both lines line that connect to the pump. 

    • The trombone line attached to the steering rack is interchangeable, as is the fluid reservoir and the steering rack itself.

  • Fuel pressure diverter valve

    • 328s have an electrically-operated fuel pressure diverter valve next to the fuel filter under the drivers seat.  The M50 engine harness does not connect to this valve, it will become unnecessary after you swap the engine.  I removed this device, kept my 328 fuel filter in its original location and connected 8mm fuel line from my fuel filter straight to my fuel rail.

  • Fuel Pressure Regulator

    • The 328 fuel pressure regulator is also down by the fuel filter.  I removed this and used the vacuum-driven fuel pressure regulator that was on my M50 fuel rail instead.

    • I believe some late 95 325s use the same fuel pressure regulator arrangement as a 328, so it could technically be Spec3-legal, but I chose to use the fuel pressure arrangement that matched the ’93 engine I was installing.

  • Fuel Tank Breather Valve

    • This is a small black solenoid valve in the engine bay on the left side, 328s have them mounted to the left shock tower.  There is a different part number and form factor for the M50 vs M52 valve.  Both versions have a 2-wire electrical connection coming from the engine harness, a large vacuum connection to the intake manifold, and a connection to a fuel vent line that goes underneath the car heading aft.

    • I recommend keeping the M52 solenoid valve; they are functionally identical.  The 12v connection and vacuum line will connect the same on both the M50 and the M52 valves, but the fuel line connection is different.  If you are keeping the 328 fuel line that runs aft, it has a different connector that does not match the M50 valve.  I kept the M52 valve on my Spec3 and it operates SAT.

  • Charcoal Canister/Evap lines

    • The 328 Charcoal canister is in the trunk and will function with an M50 engine.  I personally didn’t mess with any evap lines as part of the conversion, but…

    • When my car was at a race shop for the chassis reinforcement welding, they found some issues with my evap lines when they dropped the fuel tank and just said “they’re all messed up and some of the parts are NLA, so we just rigged up a fix and it works now.”  I have no idea what they did, but my car doesn’t smell like gas so I think it worked.  The fix was done with the M52 installed at the time and has worked fine with both the M52 and the M50 engines so I don’t think it makes a difference.

  • OBDII to OBDI Harness Changes

    • I completely outsourced this to Tulay Wireworks, no regrets; best money I spent on the project.  I have no idea what he did to my wire harness, I just said “please make this work with an OBDI M50” and it came back functional.

    • A very noticeable difference between an OBDI and OBDII wire harness is the fuel tank pressure sensor wire.  It passes through the trunk, into the right rear quarter panel and ends in the right rear wheel well attached to a small fuel overflow tank behind the fender liner.  It’s a huge PITA to disconnect the line, if I had to do over again I would just cu the line in the trunk and be done with it.  The tank/sensor can stay.

  • ABS

    • My car is an early 1996 with 3-channel ABS, the same green-label pump in a 325.  I was fortunate and was able to keep my entire brake system for Spec3.  There appears to be a part change somewhere in 1997, be mindful of the ABS pump and plumbing in a later car to make sure it is Spec3-legal.  I used RealOEM to confirm my legality.

  • Clutch Master Cylinder

    • There are two different clutch master cylinders offered in the E36, each with a different method of attachment to the pressurized clutch line.

  • ASC

    • My car did not have ASC, unfortunately I cannot comment on the impact of dealing with ASC in a 328-based build.  I assume it’s NBD since you’ll be sourcing all 325-based intake plumbing anyways.

  • Axles

    • 325 manual axles are a different part number than 328 manual axles.  I believe they are functionally interchangeable, but the 328 axles are a larger a diameter (possibly hollow?).  My original 328 axles were at the end of their service life when I got the car so I just replaced with 325 axles as part of the prep.

  • Side Skirt Holes

    • The side skirts on a 328 are not Spec3-legal. When you take them off you are left with a series of ugly holes in your rocker panels.  To fill the bodywork “the right way” was cost prohibitive so instead I had the body shop fill mine with “Christmas tree clips” (pictured below)and paint over them, looks fine from 10 feet.

  • Nose Panel

    • This is cosmetic only, but BMW did a facelift on the 3-series in Mid-96; the very first 328s did not have the facelift.  It matters if you are replacing your kidney grills (mine were busted up). Since mine was an early-96, it had the pre-facelift nose panel and did not accept the face-lifted kidney grills, which caused me a little confusion until I sorted it out.