I'm thinking the next mod to my Focus Wagon is to vent the cooling air through the hood and then fit a belly pan. I've installed a air dam
(here's the air dam) and modified my driving, with the help of a ScanGauge, to average above 30mpg. That includes time stuck in traffic, I hate seeing the 0.0 mpg on the ScanGauge.
This
thread was close to answering my question but I don't have room to modify flow after the radiator since the exhaust manifold is only a couple of inches behind the radiator.
I've read the great articles at Autospeed.com and have done some testing with a Magnehelic gauge to find low pressure areas on the hood.
What size should the vent be? Is there a theoretical size based on the size of the grill opening?