I think that the 2.4l is rated quite a bit higher on the power than the 1.8L. If you were going to replace the engine anyway, the added torque from the larger engine wouldn't hurt. You just need to find a manual trans 2.4L R/T donor car. Our 2.0 CVT2 is no powerhouse, but moves along pretty good and got 35.4mpg when I drove it for a week on my 80 mile a day journey to and from work. I imagine the 2.4L would do close to that since it wouldn't have to work as hard to accelerate. I have never driven a 2.4L in a Caliber, only a 2.4L/auto in a heavier Avenger. Cruised good but took a lot to get up to highway speed. it only had about 50 miles on it then, so it may have loosened up a little bit now. It's my niece's car.