I calculated that the extra 4 m pipework of 4 cm ID will contain an extra 5 litres of water.(Pie x r squared x length 3.1 x 2 x 2 x 400 = 4960 cm cubed = 5 litres) The pump may not circulate quite as much water per second due to the extra mass and internal friction of the water - but the inceased surface area of the pipework will act to increase the heat loss overall - so I think it will be ok.
The other question is how hot the engine bay will get ie how effective will the spoiler and louvres be? - Spacenut - thoughts?
Absolutely agree - I've found that the extra pipework aids the engine cooling, by effectively increasing the radiator surface area. I was concerned about cooling too, as everyone had these horror stories about air locks and why didn't I put the radiator in the back... like they actually knew
So I put two cooling fans on the Sud radiator wired in parallel. I needn't have bothered - on 150+ mile runs up the M1 last summer, to MITCAR, the Pod, Stanford Hall etc., the fans don't actually come on at all. Ram air flow through the radiator (and out of the extractors on the bonnet) does it all. My radiator pipes run through the sills, so do not receive any forced air flow. The engine bay is open at the bottom and scavenges underbody airflow, which as you correctly point out is then drawn up through the louvres. This is due in part to convection, but also on the move by low or negative air pressure over the top of the car - it works like an aircraft wing. The open rear panel takes advantage of this to suck the hot air through the engine bay, and the slats help to smooth the airflow, limiting turbulence, and provide a modicum of protection from the elements.
I can't see your cooling requirements being any more critical than the original 6C, which must have done a few development miles if Alfa were considering manufacture... Just make sure you can bleed out the air locks (mount header tank higher than engine and radiator, and if pipes run under the floor and then up to the radiator, have a bleed valve on top of the rad to remove any air locks in the matrix - I used domestic radiator bleed valves on mine!)