Many thanks for that.
If you've only got problems at speed, that sounds like airflow to me?
I did notice that your radiator shroud doesn't have any bypass flaps fitted?
So when running slowly you're pulling all the air through with the fan fine and you know that is working fine, but when running at speed it's the air/wind rather than the fan that is doing the cooling and in that case your cowl is actually blocking quite a bit of your rad.
I'd say one thing worth trying would be to add by-pass flaps such as these:
Just an idea
My monstrous 60mm deep Civic rad turned up yesterday, so atm I'm hopeful that it'll do the job when on the move.
And then based on knowledge gained from the Lambo experiences I just want to make sure that I've got a powerful enough fan to move the air at slower speeds.
I've got a 10" Kenlowe laying around that is rated at just shy of 800 CFM which 'may' do the job? Hence my question to see what others have used.
But jumping to 12" gives nearly 1300CFM, so a huge difference as i found on the Big Red Car!