welcome to the Mercedesshop forum. In answer to your question there are plenty of modifications you can do to the M103 engine to produce more HP. the biggest problem is $$$$.$$. My first choice would be a Mosselmann twin turbo system but I'm not shelling out $4500 for that yet. you could go for a cam but then the throttle body and exaust would have to be modified. the valve head made by Mercedes is already flawless and there is not much performance gain by porting it so im told. For my car i am planning on changing my differential to a 3.27:1 ratio wich will increase my torque and lower my max speed. basically there are positives and negitives to performance modification on the M103 engine but if your willing to invest the cash it is well worth it. i am currently having fun modifying and driving my 300E but plan on upgrading to a 500E in the near future.
Have fun and drive safely.
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!
PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320