The 86 eta motor is bullet proof but lacks the fuel, electronics and red-line to run properly and efficiently. The up-grade to 1.3 Motronics from 1.0basic Motronic is highly noticeable and recommended.
This is what I am running in my 1986 325es, stock 86 325e,es (Crank, Rods, Flat Top Pistons, head, and cam) with 1.3 Motronic Up-Grade.
*Once 1.3 Moronic is swapped in you will rev past 5300rpm so you will need to install the 7000rpm i tachometer
*Double valve springs are preferred for high rev applications but you can run the stock 86 single valve springs untill you are ready to take the head off.
Everything else if from a 89 325i 2.5
(double valve springs, valve cover, exhaust manifolds, exhaust, intake manifold, throttle body, injectors, AFM(air fuel module), FPR(fuel pressure regulator 3.0bar), all pulleys(fan, water pump, crankshaft), alternator(90 amp), belts, thermostat housing, 173ecu(computer in glove box), all 1.3 Motronic wiring and sensors, coil, wires, plugs, fuel tank, fuel pump, fuel lines,flywheel (lighter), transmission (better shifter design), starter, drive shaft, differential (4.10 from a 325ix)).
*A 30amp fuse will be needed in the fuse box for the fuel pump.
*1.3 Motronic wire harness is larger then 1.0basic Motronic harness so the inlet hole on the firewall passenger side will need to be slightly enlarged.
It seems like a long list but will only take a day or three to swap parts.
*None of the i parts will increase your rev limit (5300rpm) without the 173ecu 1.3 Motronic up-grade and for higher rev limit try out various performance chips.
After upgrading to 1.3 Motronic I now want to try the i cam in the eta head. The eta head will need to have oil passages drilled for the 3 extra cam journals at a knowledgeable machine shop.
Then I can put a 7 bearing cam in the eta head. With the i cam installed I will now have a higher power curve!
If I still want more power Ill find a 1988 325e,es 2.7 (super eta) which is the only year with 2.7 domed pistons. These pistons will mate with the i head and have proper compression for NA applications.
(e Crank, e rods, 88 super eta pistons, i head) is the most preferred and valued combination with stock bmw parts.
If I cant find the 88 super eta pistons then I will go with custom non-interference pistons that will work with (e crank, i rods, i head).
The i rods are longer then the e rods and will rev better because of the rod ratio. This combination is better then the stock parts combination.
If Turbo is in mind I will use (e Crank, e rods, e pistons, i head). Because the i head has domed combustion chambers unlike the eta head which has flat combustion chambers, the matching of the eta flat top piston and the domed chamber of the i head will result in lower compression (which is perfect for turbo applications). The i head will bolt right on to the stock eta bottom end with no machining needed. The only problem is rough idle and hard start, which can be fixed with advanced engine management.
Please ask questions and leave comments! If you need to e-mail me, my address is firstname.lastname@example.org