You'll probably just lose low end torque. The HF motor has an 8-valve head and a lower redline than the Si and DX motors, so low end torque is pretty much all you have to work with. Your time and money would be better spent swapping in a different motor. A D16A6 or a D15B7 converted to OBD-0 would be good. If you want to shoot for peak fuel economy, you might try a D15Z1, though it will be pretty wiring intensive.