Changing the suspension alone won't have any effect on your engine at all as the suspension is not connected to the engine in any way. The problem is that usually the whole point of installing a lift is so that you can fit larger diameter tires which does affect your engine. Adding larger tires won't "hurt" your engine but it may make you hate your Jeep. If you don't regear your axles your engine will struggle to turn the larger tires and you'll have a hard time maintaining highway speeds.
However if you just put a 4" lift on and keep the same tires your Jeep shouldn't drive any differently than it does now.