The 1.8T motors in the New Beetle all had 150hp as far as I'm aware, except for the Turbo S cars, which got the 180hp engine. All other 1.8T mk4 VWs got the 180hp 1.8T from '02 on (which, depending on the car, extends to 2006). The 1.8T is a 20 valve, 4 cylinder engine. Not sure what turbo is on the car. The other engines in 2003 were the 2.0L, which is non-turbo, 4 cyl, 8 valve, and the 1.9L TDI, which is a turbo diesel engine, I believe is also 4 cyl, 8 valve.
No other real differences between cars based on engine overall.
In my opinion the 1.8 Turbo engine is the best from a performance stand point. The 2.0's are good engines, just not high performance, the newer 2.5 5 cylinder was more economically feasible for the corporate bean counters, as they can use it in more models.
A 1.8 can be tuned to just about what ever you could want in a 4 cylinder engine. Is it going to compete with Mustangs, or Corvettes? No, but it will run well enough to put a smile on your face, and scare a lot of ricers to death.
I think the 1.8T is one of the most amazing motors that VW/Audi ever came out with. Totally underrated in the HP department and highly tunable. The 150HP motor can easily be tuned to 200HP with a REVO or APR tune. Install an aftermarket Downpipe, some larger injectors and get the Stage 2 Tune and you can reach 225-240 HP. Sometime even more if you upgrade the Turbo to a K4. I have the REVO tune and the difference is like night and day. The only mod that I have done to this car that you actually can feel the difference and it is a difference let me tell you. Best Bang for the buck performance mod for the 1.8 or any Turbo charged engine.
Wait until the New New Beetle hits the Road. The 2.0Liter Turbo motor is a Beast and can easily reach 280+HP with the right tune.
Yes, the Turbo Beetle's are the most Fun of the Beetle motors. The 2.0L naturally aspirated engine is lame and the 5 cyl 2.5 isn't much better. Little peppier but doesn't have the potential of the little engine that could. The 1.8T.