E30 S52 OBD2 Swap: Your Comprehensive Guide to Modern Power

Swapping an S52 engine into your BMW E30 is a popular and potent upgrade, injecting modern power and performance into the classic chassis. For enthusiasts aiming to retain the benefits of OBD2 diagnostics and emissions compliance, this guide provides a detailed walkthrough of the necessary steps. This method focuses on simplicity and effectiveness, drawing from proven techniques to ensure a successful E30 S52 Obd2 Swap.

Essential Steps for Retaining OBD2 in Your E30 S52 Swap

Maintaining OBD2 functionality during your E30 S52 swap offers significant advantages, including easier diagnostics and potential emissions compliance depending on local regulations. Here’s a step-by-step breakdown of how to achieve this, ensuring your swapped E30 remains both powerful and technologically current.

1. Wiring Harness: The OBD2 Lifeline

The engine wiring harness is the nervous system of your swap, and for OBD2 retention, using the S52 engine harness is crucial. Acquire the complete harness when sourcing your engine to simplify the process. Modification is inevitable to integrate the S52 harness into the E30 chassis, and you have two primary paths:

Professional Modification: Sending your harness to a specialist like Dave at Markert Motorwerks ensures a plug-and-play solution. They expertly modify the harness for E30 integration while maintaining OBD2 functionality.
DIY Harness Modification: For experienced individuals comfortable with automotive wiring, modifying the harness yourself is an option. However, this route demands meticulous attention to detail and a thorough understanding of BMW wiring diagrams.

Recommendation: Unless you possess significant wiring expertise, professional modification is highly recommended to guarantee reliability and proper OBD2 operation in your E30 S52 swap.

2. ECU Tuning: Optimizing for the Swap

The Engine Control Unit (ECU) is the brain of your engine, and tuning it is essential for a seamless E30 S52 OBD2 swap. Utilize the ECU that came with your S52 engine. Tuning is necessary to:

Delete Unnecessary Systems: OBD2 S52 engines often include systems not relevant or desired in an E30 swap, such as Secondary Air Pump (SAP), rear O2 sensors, Evaporative Emission System (EWS), fuel tank vent valve, and muffler flap. Tuning allows for the safe removal of these systems without triggering error codes.
Optimize Performance: A tune can also optimize the engine’s performance for the E30 chassis and your specific modifications.

DesertBMW is a highly recommended and cost-effective option for ECU tuning, known for their expertise in BMW swaps and OBD2 systems. Their tunes can eliminate the aforementioned systems and ensure your S52 ECU functions perfectly in your E30.

Tuning Cost: Expect to invest around $280 for a comprehensive ECU tune from DesertBMW, though prices may vary.

Alternative Tuning Options:

TRM Tuning
Markert Motorwerks

3. SAP Delete: Streamlining the Engine Bay

The Secondary Air Pump (SAP) system is often removed during an E30 S52 swap for simplicity and engine bay cleanliness. Since the ECU tune eliminates the need for the SAP system, physical removal is straightforward. Two methods are common:

DIY SAP Flange Welding: The most economical approach involves cutting the SAP pipes at the flanges and welding the flanges shut. This effectively blocks off the ports on the exhaust manifolds.
Pre-made SAP Delete Plates: For a cleaner, bolt-on solution, purchase pre-fabricated SAP delete plates. These plates are readily available from various BMW parts vendors.

SAP Delete Plate Vendors:

ECS Tuning
Turner Motorsport
Achilles Motorsports

4. Fueling Considerations: Adapting to OBD2

OBD2 S52 engines utilize a remote Fuel Pressure Regulator (FPR) and a fuel pressure loss valve mounted on the chassis. You have options for managing the fuel system in your E30 S52 OBD2 swap:

Retain OBD2 Fuel System: You can keep the remote FPR and associated components. This maintains the original OBD2 fuel system design.
Convert to OBD1 Fuel Rail: A popular alternative is to switch to an OBD1 M50 fuel rail and FPR, often paired with an M50 intake manifold upgrade (discussed in the next section). This simplifies the fuel system and is compatible with the M50 manifold. Minor modification to the M50 fuel rail tabs might be needed for S52 harness injector plug clearance. Early OBD-II fuel rails from E36 328i or E39 528i models offer an FPR on the rail and maintain fuel rail cover compatibility.

Recommendation: The M50 OBD1 fuel rail conversion is often preferred for its simplicity and compatibility with the M50 manifold upgrade.

5. M50 OBD1 Intake Manifold: Unleashing Hidden Power

While not mandatory for an E30 S52 OBD2 swap, upgrading to an M50 OBD1 intake manifold is a highly recommended performance enhancement. The M50 manifold is known to provide noticeable power gains over the stock S52 manifold, especially in the mid-range.

M50 Manifold Conversion Kits: Several kits are available to facilitate this swap, including necessary adapters and components.

M50 Manifold Kit Vendors:

M50manifold.com
Turner Motorsport
KO Performance

Intake Boot and IAT Sensor: Utilize a long OBD1 intake boot (from an OBD1 E36 M3 or 325i) with two ports underneath. One port connects to the Idle Control Valve (ICV) hose. For the Intake Air Temperature (IAT) sensor, you have two main options:

Mount IAT in Intake Boot: Drill and modify the second port on the OBD1 boot to accommodate the OBD2 IAT sensor. This is a preferred method as it positions the sensor optimally in the intake stream.
Relocate IAT to OBD1 Manifold Location: This involves re-threading the OBD2 IAT sensor to fit the original OBD1 IAT location on the manifold, which is generally less ideal than boot mounting.

OBD1 Intake Boot Part Number: 13541738757

6. Dipstick Modification: CCV Integration

If you are retaining the Crankcase Ventilation (CCV) system, modifying the dipstick is necessary to allow CCV drainage. Use an E34 M50 dipstick and modify it as follows:

Cut the drain pipe from your S52 dipstick.
Drill a hole in the E34 M50 dipstick.
Weld the S52 drain pipe onto the E34 dipstick.

7. Coolant Lines: Adapting the Cooling System

For E30s with a late-model 325i cooling system, S52/M52 coolant hoses are largely compatible. An E36 Mishimoto radiator is mentioned in the original article, but it is not recommended due to reported reliability issues. A Z3M radiator is a superior alternative.

Coolant Hose Setup:

Top Radiator Hose: E36 S52 hose (no trimming needed).
Bottom Radiator Hose: NAPA NBH 8484 hose (cut to length). Avoid using a cut S52 hose as it may kink.
Expansion Tank to Metal Pipe: Cut piece of long S52 hose.
Heater Core Hoses: Back of head to bottom heater core, back of metal pipe to top heater core.
Throttle Body Coolant Lines: Optional to delete in warmer climates for a cleaner engine bay. If deleted, cap the coolant pipe fitting.

8. Coolant Temperature Sensor: E30 Gauge Compatibility

To ensure your E30 cluster temperature gauge functions correctly, use an E30 brown top coolant temperature sensor. This replaces the throttle body coolant line pipe on the S52 head. Options include:

Option 1 (Thread Die Modification): Modify the threads of the E30 sensor to match the S52 head using a die (M12x1.5, verify pitch).
Option 2 (Head Tapping): Tap the S52 head to match the E30 sensor threads (riskier).
Option 3 (Pre-modified Sensor): Purchase a pre-threaded brown top sensor from vendors like Markert Motorwerks.

Basic Swap Steps: Transmission, Differential, and More

Beyond OBD2-specific considerations, several fundamental mechanical steps are involved in an E30 S52 swap.

9. Transmission: Choosing Your Gearbox

ZF Transmission (E36 M3 or 328i): Direct bolt-in to the E30 chassis using 318is/325i transmission braces. Use E36 M3 or 328i shift linkage.
G260 Transmission (E30 M20): Requires a custom or aftermarket transmission brace (e.g., from White325is). Selector rod modification (twisting or UUC DSSR) is needed due to the G260’s angle.

10. Differential: Optimizing Gearing

Any E30-compatible differential can be used. A medium case differential is recommended for durability, with a 3.25 LSD being ideal for S52 power. Lower ratios (numerically higher) like 3.73 or 4.10 can be used for M52 swaps or if more aggressive acceleration is desired.

11. Driveshaft: Connecting Power to the Wheels

1986-1987 325e Driveshaft: Compatible with the large front flange.
1996-1999 M3 or 328i Driveshaft: Direct bolt-up to E30 differential with a 4-bolt rear flange.
Revshift Adapter Guibo: Allows use of the stock E30 driveshaft.

12. Brake Booster: Clearance Solutions

Option 1 (Relocate Stock Booster): DIY relocation (refer to hwy84’s guide on r3vlimited) is considered the best for maintaining brake pedal feel.
Option 2 (E30 325ix Booster): Potentially bolt-in (requires further research).
Option 3 (E21 320i Booster): Requires clevis shaft shortening and re-threading. Pre-modified units are available from Zionsville.
Option 4 (Porsche 944 Booster): Input rod shortening and threading needed, but compatible thread pitch.

13. Engine Mounting: Securing the S52

E36 Aluminum Mount Arms: Essential for mounting the S52 in the E30. Acquire these with your engine if possible.
Engine Mount Options:
- E28 535i or M5 engine mounts.
- Aftermarket 24v mounts from vendors like Condor Speed Shop or AKG Motorsport.

14. Oil Pan: Front Sump Conversion

S52/M52 engines have a rear sump oil pan, requiring conversion to a front sump for E30 clearance.

Components Needed:

E34 M50 oil pan
E34 M50 oil pickup tube
E34 M50 dipstick tube and dipstick (modified as per step 6)
E34 M50 oil level sensor

Conversion Process:

Remove original S52 oil pan, pickup, and windage tray.
Cut the bracket for the S52 oil pickup tube (or bend it off).
Install E34 M50 pickup tube with a new gasket.

Optional (but Recommended): Secure the oil pump nut using safety wire and red Loctite or tack welding.

Oil Pump Nut Vendors:

Rally Road
BimmerWorld

Install new oil pan gasket and E34 M50 oil pan, applying silicone sealant at block/timing case and block/rear main seal cover cracks.

15. Throttle Cable: Ensuring Proper Linkage

An E34 M50 throttle cable (Part Number: 35 41 1 160 609) is required. Install before brake booster relocation for easier access. A 318is throttle cable mount can improve cable stability.

16. Cooling Fan: Electric Fan Conversion

Due to the S52’s length, mechanical fans are often replaced with electric puller fans in front of the engine or pusher fans in front of the radiator. Refer to Dave’s electric fan write-up for detailed guidance. SPAL 16″ pusher slim fans are a cost-effective and quality option.

Recommended SPAL Parts:

Fan: 30100401 (16″)
Gasket: 30130074
Mounting Brackets: 30130011

17. ECU Mounting: Securing the Brain

Use E30 318is ECU mount brackets (or similar). Relocate brackets rearward for adequate ECU connector clearance.

Reverse Lights: Wiring the Backup Function

Connect reverse lights by splicing an E36 two-prong plug into the E30 reverse light wiring under the shift boot, matching the E36 transmission switch.

Tips for Engine Drop-in: Making Installation Easier

Engine and Transmission Assembly: Install engine and transmission together for easier drop-in.
Intake Manifold Removal: Drop engine in without the intake manifold for better clearance.
Load Leveler: Use a load leveler to adjust engine angle during installation. Shorten front chain, lengthen rear chain for optimal angle.
Helper Assistance: At least one helper is essential, two or more ideal.
Mounting Strategy: Bolt engine mounts to subframe first, then align engine onto mount studs.
Protective Measures: Protect car’s front support and other areas from scratches during engine installation.
Transmission Jack: Use a jack on the transmission to fine-tune engine leveling.

Enjoy the enhanced performance of your E30 S52 OBD2 swap! If any crucial information is missing, please provide feedback for future additions.