Just because it has good compression across all four cylinders dont count for squat, its when its on boost the damage gets done as the head will lift a tad and this boost pressure will find its way past the round sealing rings on the H/G and in to the water ways hence pushing the water out of your header tank. Once you get this little issue sorted it will cope with that power you are after with EASE for a long time if maintained well.

If you was close id be round there now stripping it down to help you out.