Intercooling

[nissannewby]

On a 4.2 turbo diesel in a 1999 gq which would be the way to go an air to air intercooler or a water to air intercooler
cheers

[cooki_monsta]

water to air if u can afford it air to air if you cant

[PGS 4WD]

Air to air is generally the most efficient but is the most difficult to fit. Many of the small water to air coolers are very inefficient as their surface area is insufficient, they are low in restriction but the air speed through the core is so high the amount of actual cooling is minimal, this is typical of the smaller barrel types available. Water to air coolers also need two heat transfers, so efficiency is reduced. Water systems have longer heat soak proberties so under constant load at low speed will cool for longer, but once hot will take longer to recover to normal operating temperature.
Water to air coolers are often used in high performance drag racing applications where the water is cooled in an ice box arrangement for better than atmospheric temperature cooling.

Joel