new engine

How much do you want to spend , how much HP do you expect . Why do you need an upgrade ? not enough kick at the stop light or on the highway ? Cheapest route is probably a 360 , right there you have the extra cubes and torque , 318 will be next in line . But if you want mega HP and TQ be prepared to spend .
For just cruising around a 360 would be hard to beat for the $$ You can probably find a GOOD running used 360 for under 800.00 tat would be a good upgrade