By Tom McKenzie with help from Michael Avedis
First let me explain the reason for the conversion. I purchased a 1980 323i with the original engine and K-Jetronic injection. In order to get the car California "smog legal" I was faced with taking the car to a state lab where they would fit an aftermarket oxygen sensor, charge me $2000 and not guarantee anything. The other option was to install the complete engine and injection from a 325i (E30). I decided on the latter because I would have a low mileage motor with an opportunity for upgrades (i.e. chip etc.). I was able to find a 1991 325i motor with injection, brain and air box with 35K miles. Note: If you have a 320i you will need to obtain a 323 subframe. I'm not familiar with this procedure. Most of this article will assume you have a 323. (Webmaster's note: For info on putting a small six into a 320i, see the other engine swap page.)
Old Motor Removal/Engine Bay Preparation
I removed the old motor by renting a hoist and using my 320 Haynes manual. Everything is straightforward. It did take some time to jockey the motor out but I was doing it by myself. Having a couple of buddies around is highly recommended. This also allows plenty of opportunity for Tim Allen impressions. You should remove the battery tray and old air filter bracket at this time. Michael had his engine bay repainted.
Now you need to figure out what you need from the old engine. Michael used his 323 flywheel because it was lighter. You will also need the old 323 motor mounts because the 325 mounts are wider. I purchased a new clutch since I had the engine out. Some people recommend using the 323 oil pan but both Michael and have had no problems with clearance using the 325 pan. Michael and I both used a early 325 water pump so the expansion tank could be used. I had to trim some material off my 323 plate that fits on the bottom of the transmission. Michael used the 325 plate. You should also plan your exhaust arrangement. I used the stock 323 arrangement and had an O2 sensor welded into the downpipe. Michael used his headers and also had a O2 sensor welded in. I initially purchased a used sensor but I would recommend buying a new one since I ended up getting a new one shortly after. You will also need some of your 323 hoses for the radiator. My engine had a pipe mounted on the front of the block to route coolant which I removed since the 323 radiator's bottom connection is on the other side.
I purchased a combination battery holddown/rear strut tower brace from Top-End performance. They provided everything required to move the battery to the trunk. I ran the cable along the right side of the car under the carpet and through an existing hole in the firewall. I purchased a 325i battery junction and used this to branch to all the 12V wires. Note: the 325 has a fusable link which is used for power to the harness.
This part takes some soldering expertise. You can cross-reference from the 325 ETM and your 323 manual. Pete McHenry also has wiring setups available, and there is some wiring information on Brandon's site too. Some of the wires from the 325 aren't used. Micheal found the wire that runs from the end of the engine harness to the fuse box (E30). I wired directly from the engine harness to my e21 fuse box using the E21 15 pin connector. I'm in the process of working up a wiring diagram.
The 325 oil filter base has outlets for an oil cooler. I removed the base and installed my oil cooler base. Michael didn't have an oil cooler so he removed the base and used the threaded sleeve from his 323 motor.
The 325 cable can used with some modification. On the pedal end I just hooked the cable in the slot. On the throttle end I used the stock location for the rubber grommet but the cable was too long so I routed it up where I think the automatic transmission cable would go. So now it's at a slight angle.
The vacuum hose from the 325 motor hooks right up to the brake booster. I used the same hose although it's probably a little short.
You need to drill a hole in the firewall for the brain. I chose to mount the brain in the glove box so I drilled 2 inches to the right of the hole where I ran the battery cable. You can then seal the holes with silicone. I used tie wraps to attach the brain to the rail running above the glove box. I'll eventually bolt it down. There are two connectors which are used. The only thing you need to connect is the 51 pin connector to the brain.
You should be able to use the 323 fuel pump. Just check the output pressure to make sure it is within specs. You might want to change the filter.
You can use your 323 alternator if you modify the harness since the 325 uses a different type of connector. My 323 alternator was only rated at 80 watts but since I don't have A/C this wasn't a concern.
Questions? E-Mail Tom.