Stevin..
Firstly, the 325iS Evo has alum panels, I know that cos both my red and a maroon Is had those panels, if you read the CAR test on the Evo 1, the mention that the alum panel where sourced and pressed from a company in Sweden, all to save weight, the bonnet on the Evo1 is alum as well...
engines difference included, (as far as I'm aware), the ev0 1 had a smaller AFM compared to the Evo2, the Evo1 had no exhaust branch, both my cars had manifolds when i bought them, compared to the Evo2, which had a local manufactured branch, which was made by BOSAl SA, i know this cos BMW referred me to them when i was looking top replaced my std manifold on my red car, the branch from bosal is R7500, thats just the branch!!
The inlet valves on the Evo2 were larger that the Evo1, which was used to improve the mid-range of the car, the Evo2 had a short ratio diff, however both cars topped out at 228kph as tested by CAR Mag, just short of the claimed 238Km by BMW, however CAR does mention that the claimed speed by BMW is well within reach, but due to the fact the when CAR tested both vehicles a full tank of fuel, together with a 2 man crew and testing equipemnt was in the car, therefore increasing weight on the vehicle.
The under floor tray found on the Evo2 was deveopled to improved under car air flow, to assist with cornering , for the stannic group N, since the opels where so light, they had a huge advantage. The interior of the cars where the same , except that leather interior was std on the evo2 and optional on the evo1, including the sunroof. The rev limit was increased to 6750 on the Ev02, where as the evo1 was set at 6700 ( i stand corrected here)
These are just some of the changes I can think quickly...
as far as speed is corcerned, the evo2 is slighty faster, and only through the mid range, however a well tuned STOCK STOCK evo1 will run away from a Evo2, as i use to ..kill them with my stock evo1... even with a stock both end (2.7) like i had, with a few mods...one can have some fun.