2.) Cylinder Head
Obviously, you'll need a complete 325i cylinder head for this project unless you have an '88 325 or '88 528e (in which case you already have one, but you'll need to get a 325i cam and set of dual valve springs). I purchased my cylinder head used from someone who dropped an M50 into his 325is. Unfortunately, it was in less-than-perfect condition as there was a lot of carbon buildup on the valves, the guides and seals needed replacing, and the cam lobes looked pretty worn, so I had everything redone at the machine shop: new valves, guides, seals, and even a new cam and rocker arms. I also had a newer set of valve springs installed. I pretty much ended up with a brand new head, especially considering how much I paid for everything, but at least I can sleep well at night ;). You can also install a hotter camshaft, titanium valve springs, larger valves, etc, but I chose to leave everything stock.
Use the stock head gasket; do NOT use the oversize (thicker?) gasket because it will lower compression and render your $1,000 pistons useless. The stock gasket will work with +1mm overbore pistons, but if you go +2mm then you'll probably need a special oversize one.
Fortunately, BMW designed the gasket to fit only one way (unlike, say, a Honda Civic), so there really isn't any way of putting it on backwards. Align the head with the gasket and block and it will sit right on top. Lubricate the E14 torx head bolts with oil, then initially torque them down to 30 lb-ft. Retorque them 90 degrees after a few minutes, then again once the motor is installed and the engine has been run.
Adjust the valves to 0.09" for the intake and 0.10" for the exhaust. You'll need a 10mm wrench, feeler gauges, and the valve adjusting tool. If you don't have the valve adjusting tool, then break off the antenna off your neighbor's Acura and bend it 45 degrees. That also works just as well :). Turn the crankshaft with a 22mm wrench to get the cam to move. Then add the four rocker shaft plugs and valve cover gasket.
Install the exhaust manifold gaskets and exhaust manifolds. Tighten the bolts down to 17 lb-ft.
Paul installed the timing belt and tensioner for me, but being the ace BMW mechanic that he is, he screwed that up (everything came loose at about 1000 miles) so if you're unsure how to do it, better check the trusty Bentley ;).
3.) Fuel Injection
Start off by installing the fuel injectors onto the fuel rail. I decided to use M50 injectors because of its higher flow rate, as the stock 325i injectors are known to lean out at very high RPM.
You can also use injectors from a 535i/635i/735i, or Ford Mustang 5.0, though each one has a different flow rate. So which one should you buy? Depends on what works for your application. To figure out how much power an injector is good for, take the flow rate (cc/min) and divide it by 5. That will give you the maximum horsepower that injector can support. Multiply that number by 6 and that will tell you how much total horsepower all six injectors can support. (This formula assumes zero injector clogging, 100% injector duty cycle, and 14.7:1 air fuel ratio. Since injectors tend to clog over time, 100% duty overloads the injectors, and 14.7 isn't always a constant, it is better to get injectors that moderately exceed the amount of power your car will produce.) For example, the stock E30 325i fuel injector is rated at 149cc/min. Divided by 5, it can support 29.8 horsepower per injector, or 178.8 max brake horsepower. That's sufficient for stock 325i's, but for modified cars, it's not good enough. Here' are a few upgrades you can use:
S52 injector (from E36 M3 [1996+], M Coupe, M Roadster)
BMW Part Number: 13-64-1-703-819
Bosch Part Number: 0-280-150-440
Flow Rate: 205 cc/min
Maximum HP Supported (100% DC): 246
Ford Mustang 5.0 injector
Ford Part Number: FOTE D5B
Bosch Part Number: 0-280-150-556
Flow Rate: 200 cc/min
Maximum HP Supported (100% DC): 240
M50/M52 injector (from E36 325i/325is/323is)
BMW Part Number: 13-64-1-730-060
Bosch Part Number: 0-280-150-415
Flow Rate: 190 cc/min
Color: Pale Green
Maximum HP Supported (100% DC): 228
M30 injector (from E28 535i/535is, E24 635CSi, E23 735i)
BMW Part Number: 13-64-1-276-149
Bosch Part Number: 0-280-150-203
Flow Rate: 185 cc/min
Maximum HP Supported (100% DC): 222
Replace the injector o-rings (there are two per injector, P/N 13-64-1-730-767), but be careful not to break the cap on top. I actually cut the top o-rings out. Apply grease or gear oil on all the new o-rings, then slide them onto the injectors. Pop each injector onto the rail, then secure each with the plastic clip. Install the 325i fuel rail onto the intake manifold and tighten the four 10mm bolts to 8 lb-ft.
Later model 325i's use a secondary harness just for the fuel injectors, unlike the 325e's wiring harness which connects directly to the injectors. Because of this, you should use the 325i fuel rail because the 325e's fuel rail has an outlet for a return line right next to the #6 injector. If you do use the 325e rail, you'll have to figure out a way to wedge the 325i's harness rail underneath it without breaking anything.
Earlier wiring harnesses (1987 and 1988) had individual connectors for the fuel injectors and do not have a secondary wiring rail. If you are using this earlier harness, then you may be able to get away with using the eta fuel rail.
Place the intake manifold gasket against the head, then align the manifold with the studs and tighten the bolts to 23 lb-ft.
Install the block breather tube by compressing the spring (I used two tip ties to hold it in place), then aligning the tube from the block and manifold. Once it is sitting in place, push the bottom spacer to the block then cut the zip ties so the spring releases. The tube should hold in place now (see picture above).
Now for the fuel management system:
First off, you'll need a Bosch Motronic 1.1 or 1.3 ECU instead of the Motronic 1.0 unit that's currently in your eta. The 1.1 system has a reputation for bad idle problems, so you'll probably want to use the 1.3 unit instead. (The 1.1 can be easily identified by its Bosch number, 0-261-200-153.) There are several 1.3 ECUs available and they are all the same; 0-261-200-173, 0-261-200-380, 0-261-200-524, or 0-261-200-525. They came from the 89-91 325i's and 89-90 525i's. The one I have is the *525 from an E34.
The wiring harness may look daunting because it is a jumble of wires and connectors, but if you trace the harness starting from the ECU connector, you can figure each one out. If not, don't worry, I got you covered (see page 6). But I chose not to wire it on the stand because most of the connections were outside of the engine. All I did was connect the fuel injector rail to the harness so it was attached to the engine.
But before I could put the 2.8 in, I had to take the old 2.7 out. Time for the good ol cherry picker!