How can you manually turn on the radiator fans and will this help fight off detonation under heavy loads during hot weather?

 

It is possible I'm sure to manually turn on the fans by installing a switch wired to 12V. Not sure how much it will really do though. If you're really worried about hot temps, you might want to think about a water mister setup.

 

If your intercooler isn't doing the job the only other way to go is lower compression or higher octane petrol.

 

Or get a intercooler misting system.

 

New radiator / larger oil pan maybe?
Doesn't help intake temps but overall engine temp.

What's the typical intake temp for twin turbos under high load?