If your only looking to spend around 500 on the motor itself then you should go with the ZC. Its a 1.6L non-vtec and pulls out 130 hp. This doe not include any of the upgrades you can do to them. Plus you can find good deals on them. I am getting for my 88 Crx hf a ZC motor, stage 2 clutch, so tranny, wiring harness, and ecu, for 800. These are definetly the leats expesive, with the most potential!