Loading ...Q I have a 1985 325e with the 2.7-liter, 6-cylinder engine. I am looking to build a high performance motor for this car. Any info would be appreciated.
James W.
A There are many ways to improve upon the performance of your 325e. How fast you can go depends on how much you’re willing to spend. While it is possible to build a pretty hot “e” motor, it is costly to do so. Another option might be to start with the engine from an 87 thru 91 325i. (Both are called M20 engines.) First, let’s look at the major differences between the 2.7 engine from your 325e and a 2.5 engine from the 325i.
- Crankshaft: 2.7 is longer stroke than 2.5 for added torque.
- Connecting rods: 2.5 are longer than 2.7, which decreases piston wear.
- Cylinder head: 2.5 has larger intake ports and intake/exhaust valves for higher RPM.
- Intake manifold: 2.5 has larger ports for better flow at higher RPM.
- Throttle body: 2.5 is larger for better flow at higher RPM.
- Air flow meter: 2.5 is larger for better flow at higher RPM.
– Redline: 2.7 redline is 4800; 2.5 is 6500 for more top-end HP.
- Engine management system: 2.5 is designed for the higher RPM and HP.
Here are three options for building a more powerful M20. All of these assume the use of performance headers, intake kit, adjustable fuel pressure regulator, high-performance ignition wires and a performance chip.
1. Naturally aspirated, long stroke, 2.8-plus:
The hottest setup is to use the longer stroke 2.7 crankshaft or the 524td crankshaft, which is the same as the 2.7 crank except that it is forged (if super/turbocharging is planned, I would use the forged crank). Both the 2.7 and the 2.5 blocks are the same so you can use either one. Use the connecting rods from the 2.5 engine, which are longer than the 2.7 rods and give a more desirable rod/stroke ratio and less cylinder wall side loading. With this combination, custom forged pistons are required due to the longer stroke of the crank and the longer rods (the piston pin must be mounted higher in the piston); the pistons should be 1.0 mm oversize. Use the 325i head with a good three-angle valve job and the complete fuel injection system from the 325i. While this combo will work with a stock 325i camshaft, a Schrick cam with longer duration and higher lift will fully capitalize on the bottom end/head combination. (Note: you must have performance headers and a PowerFlow intake to see the proper power gains.) Finally, all of this will require a custom chip for the ECU (Engine Control Unit).
2. A cost-conscious 2.7 M20:
Do a stock freshening up of the 2.7 bottom end – bearings and rings (pistons if desired or needed, depending on current wear). Install a freshly rebuilt head from the “i” (do a three-angle valve job), along with the complete intake and engine management system from the “i”. First stage would be to use the stock “i” cam. Second stage would be to use a Schrick camshaft. The standard performance chip we offer would work well with this combo (in the “i” ECU). This can be a very peppy 200+ hp engine.
3. A cost conscious 2.5 engine:
Similar to the 2.7 engine above, but using a complete 325i 2.5 engine. This combo will rev quicker than the 2.7 above, but will not have quite as much torque in the lower RPM. Again, this will produce around 200+ hp. A higher revving 325i or built up 325e motor will benefit from lower gearing in the differential in order to rev more freely. This would also come from a 325i (3.73:1). The engine management, fuel injection and intake system from the 325i flows much more air than the “e” parts and really should be used when looking at gaining higher horse power. Again, this leads back to swapping in the complete engine and engine management from an “i” car.
Depending on which upgrade you choose, there are other potential mods you may need to perform (e.g. swapping instrument clusters or ECUs). Bavarian Autosport can provide everything you need except the complete engines. If you have further questions or wish to place an order and get this project going, feel free to contact us.
