Warning: I don’t do rear mount setups. This is simply a brain dump of my current understanding.
Drifting at the professional level, rear mount radiators are becoming very common. There are many good reasons and a few reasons not to do this.
- Theoretically better weight distribution
- More space to run ducting in and out of the radiator
- More fluid to dissipate heat
- Leaves more room in the front for other coolers
- Allows for more front crush area so that hits don’t cause fluid spills – Rear location can also still allow for rear hits without puncturing the radiator
- Potentially horrible air flow through radiator
- Added weight of extra liquid
- More parts means more things to break/puncture
Rumors (that I can’t fully confirm or deny):
- Harder on water pump
- More difficult to bleed (Shouldn’t be an issue if it’s the highest point of the system)
Realistically, unless the car is designed for pro/am or higher levels, I don’t think the effort is truly worth it. The main reason to do this seems to be to allow for better crush zones. The early days of D1/FD had lots of contact that caused cars to be done for the weekend. Now, with the advent of multiple level crash systems (aluminum into steel into factory frame), cars can get bashed up significantly on the outside but still drive fine. At an amateur level and even at a lower cost pro/am level, this seems more expense than benefit.
Regardless of that, the key to doing a proper rear mount setup seems to be ensuring that the radiator fill point is the highest point in the cooling system. Flat mounted to the floor of the trunk seems to be a bad idea for this reason and for basic air flow. Even with it floor mounted, I would be worried about debris and tire bits blocking off flow. The factory water pump seems to do the job in most setups I’ve seen. A secondary electric pump could be used for security. A basic rear mount radiator seems simple and straight forward otherwise.