A really good engine will cost twice as much as you pay for the car. Once again, you need to specify a budget so we can make some suggestions. I could say go ahead and put a $600 Italian engine in there, and then you would need to consider a few upgrades.

You really need to think objectively about what you want to do with it. If mad speed is what you want, get te Virus and the 30 pound brushless conversion set, and put a crazy electric brushless setup in it, but then you will need batteries, chargers, etc. Same with engines though. All the really good engines are sealed (no pull starts, etc), so you would then need a starter box and batteries for the starter box, and a charger for the batteries, etc etc.

As the old saying goes...Speed costs money, how fast do you want to go?

There are some good budget engines with pullstarts for sensible money, so how much do you want to spend?