The main differences between the 325i and the 325e are in the engine. Although both models have engines from the same M20 family, the 325e had more displacement (2.7 liters versus the 325i's 2.5) but drastically less horsepower. The 325e redlines at a very low 4800 RPM and only had 121 hp @ 4250 RPM but 174 lb-ft of torque @ 3250 RPM and an incredibly flat powerband to compensate. The "e" stood for "eta," which is the Greek letter for efficiency and was the theme for the 325e. It also had a very conservative 2.93 rear gear (2.79 in the earlier models) to allow low freeway RPMs and higher gas mileage; in contrast, the sport oriented 325i had a much shorter 3.73 rear end (4.10 in automatics). Although the "i" models had a smaller displacement engine, it had much more horsepower: 167 horsepower, 164 lb-ft torque and a higher compression ratio (9.7 vs 9.0).
As a result of its peaky powerband, the "i" also had a higher redline at 6700 RPM.
As a side note, any model with simply a "325" designation is equipped with the 2.7 liter eta engine. It was BMW's base model from 1986 until 1988 when it was phased out of production in favor of the 325i. In its final year, the 1988 325 (dubbed "Super Eta" by enthusiasts) was equipped from the factory with special pistons, 325i head/exhaust system, and Motronic 1.1 engine management control, bumping horsepower up to 127 and raising the redline to 5500 RPM.
Any model with an "s" suffix, like the 318is, 325es, and 325is, denotes the sport model which only came in two door form. It can be easily recognized by its front spoiler with integrated foglights, rear decklid spoiler, and 14" BBS cross-spoke "basketweave" rims. It also featured a limited slip differential (optional on the 318is) , bolstered sport seats, thicker swaybars, slightly stiffer shocks and front springs, and 3-spoke sport steering wheel (except '90 on, which used a leather-wrapped airbag wheel). The 325es and 325is came with an on board computer, power sunroof/mirrors/windows, central locking, and premium sound system standard as well. In 1991 there was no official 325is model, although the Sport package with all the aforementioned items was still available.
The "X" denotes all wheel drive and only came in 325iX form (there was no such thing as a 318iX or a 325eX). It shares major components with the rest of the 325i, but uses a different oil pan and pump because of its front drive axle and comes with 15" rims (and unique +41mm offset). It also featured side skirts and slightly flared fenders to differentiate itself from other 2WD models.
The "c" denotes a convertible, although it is not an official BMW designation. Rather, it is used by dealers and owners to easily identify a convertible model. BMW North America imported the 325i convertible in 1987 and the 318i convertible in 1991; both of which were still in production in 1992 when the E36 was released, as is BMW's policy to overlap convertibles into the next generation until their replacements are ready.
What about the racing derived M3? It shares very little body parts with other E30s and comes with a completely different motor. The M3 is very easily identifiable with its body coloured bumpers/mouldings/mirrors, front spoiler, flared fenders, rear valence, rear wing, high trunklid, rear window clip, and roof mounted antenna. It's engine, the S14 DOHC 2.3 liter 4-cylinder producing 195 hp @ 6750 RPM/166 lb-ft of torque @ 4750 RPM, was derived from the 3.5 liter M5 6-cylinder and was intended for motorsport use. It featured a very peaky 7100 RPM redline, 10.5:1 compression ratio, 4.10:1 LSD and short ratio gearbox. The M engineers also equipped it with a larger 18.5 gallon fuel tank, 5 lug 15" BBS cross-spoke rims, and upgraded brakes (thicker and larger diameter ABS-equipped discs, heftier callipers, and a revised master brake cylinder). Interior upgrades were limited to red gauge needles, oil temperature gauge (in place of the standard fuel economy gauge), sport steering wheel, leather sport seats, rear armrest (replaced the center seat) and the M logo on the instrument cluster, door sill, and shift knob.
In stark contrast to the M3 was the 318i. The 1984-1985 318i's engine was a slightly modified version of the M10 motor used in the previous generation E21, putting out only 101 hp @ 5800 RPM.
It had the basic L-Jetronic engine management system (as opposed to the Motronic used in the 325e/i models), rear drum brakes, and limited standard equipment. It was hard pressed by its competition and was finally dropped after the 1985 model year. However, the 318i moniker returned for 1991 but with a brand new 1.8 liter, 16-valve DOHC motor producing 134 hp and 128 lb-ft of torque. Although it lacked the uplevel features of its 325i stablemate, it provided lively performance at an entry level price. http://www.bmwe30.net/cgi-bin/datacgi/data...0127&Section=14
Here is a link to all the engine specifications. http://www.bmwe30.net/cgi-bin/datacgi/data...cles&Section=07