Dude - I am STILL looking into this myself. I have found that the area where I'd like to chop bonnet (higher, towards windscreen) will actually have air PUSHED INTO IT at anything around 80km/h or above. This may not be such a big issue, but will have to do a decent pressure check around the front of the block and in front of extractors to see if there is still enough air pressure differential for the radiators to work.

I think it will be fine - Especially is a put the belly pan back in so that the engine bay is vented along entire width for about two foot in front of fire wall on bottom of engine bay.

When idling around town the heat should escape out holes further up the bonnet fine... Although, to increase airflow through the radiators and actually allow the waste hot air out you need basically a big slit through the bonnet about a foot to 16 inches behind the radiator --- like a late model Mitsi Evo .

Started mucking around taking pressure readings at different speeds the other weekend. My testing system needs some work, but first results seem to confirm that pressure from the windscreen does actually create enough of a "bow wave" to push air INTO the engine bay if you "vent" the engine bay within a foot of the windscreen....

Will attempt to find a slightly less error prone system for checking it and do a grid over bonnet and try all sorts of positions and the corresponding positions under the bonnet.

If anyone has done this with an EF Fairmont I6, you could save me a couple of days effort by replying here.


Cheerio.