I didn't intend to be hostile or confrontational just so you know.
The 2.5 and the 2.7 are *essentially* the same engine. There are some noticeable differences. They can share plug wires though.
My 2.7 was designated M20B27.
Your brothers 2.5 is the M20B25.
The B27 was designed to be a low hp/high torque gas mileage queen. And mine was, it returned 35mpg when I bought it and about 27mpg when I sold it. I did a few modifications, more on that at the bottom.
The B25 was designed as the high hp/low torque gas mileage be damned car. They still return around 24-26 mpg which is perfectly acceptable in my book.
Now they share a common block, starter, airbox, cables, belts, pulleys, plug wires, accessories, etc.
The difference lies in the engine computer, pistons, con-rods, crankshaft, cylinder head, intake manifold, throttle body, and fuel injectors. This is somewhat simplified as there are some other small different bits and bobs. Sensors related to Motronic 1.0 (325e) and Motronic 1.1/1.3 (325i) are also different obviously.
This might sound extensively different and it is... but all these bits and pieces are interchangeable and will bolt on to either engine. The resulting combination might not run well at all, or pistons might hit valves but in the end everything is interchangeable.
There are several routes to high performance with these engines as well.
You could build a 2.7 stroker which is essentially a 325e block and conrods with SuperEta pistons and a 325i cylinder head, intake manifold, and engine computer.
You can put an i head on an e block and turbocharge to around 6-7 psi without o-ringing the head or adding an intercooler. Engines have been built to handle around 24 psi, but this is quite extreme.
The easiest way to power if you have an e is to put a E21 323i head on the e block and use an i engine computer, fuel injectors, and intake manifold. Expect around 160 hp, lower than the stock i at 171 but considerably higher than the stock e at 121.
The hp of the stock e might sound a bit low, but this is where the beauty of 80's BMW's and interchangeable parts comes in. I had the ports machined out to fit i valves and I installed all new i valves, i double springs (the etas are single spring and prone to failure at higher rpms), i cams, rockers, and retainers. Then I installed an i intake manifold and throttle body. Still on the stock e computer I installed the common and excellent MarkD 89 Octane 325e chip. This raises the rev limit from 4600 to 5600.
The car shed some weight in the form of the massive rubber sound deadening in the trunk, underneath the carpet, underneath and behind the rear seats, spare tire, jack, glovebox, AC compressor, power steering system (Euro manual rack installed), and radio. All told over 150 pounds came out of the car. I had it weighed by our kindly local landfill and it came out to 2,384 lbs with a half tank of gas and without a driver.
Next up were the iS rims and 225 width tires front and rear. M3 sway bars, sway bar end links, control arms, and control arm bushings were installed. Finally a 535i's 3.25LS diff replaced the stock open 2.79.
The little eta was a screamer compared to its previous boring life as a gas mileage granny coupe. With its very high torque and very short gears, the car could take even S2000's and RX-8's off the line with no problem. They catch up once you get above 55 or so, but the look on their face as they finally hit *some* torque and pass is just gold.
Chapter 6
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Just kidding. Sorry I wrote a book about it... I just love the 80's 3-series.
.S. x2 Don't get me wrong I have nothing against BMW's reliability
