Would anyone know how I can work out the minimum diameter for the intake hose on a 1900cc VHPD with out causeing an air restriction.
Cheers in advance. 
Surely its 4 x your throttle body diameter cross section? As thats your next restriction.
Maybe, but only one cylinder draws air in at a time. I wonder if there is a secret formula???
The stock hose is massively oversized. I’d think you could go down to 70 or 80mm easily.
I,d say as a minimum the same area as 4x 48 mm trumpets .
So …
Pi x radius squared= area
3.142 x 24 x 24 x 4 (trumpets)=7239 mm2
3.142 x 48 x 48 x 1 (trumpet) =7239 mm2
So your intake needs to be 96mm diameter !
I’m guestimating from what I used to know from 48 mm trumpets on Weber DCOE carbs which were good for 250 ish bhp…
A 150mm diameter hose is good for up to 650bhp without forced induction! Though on elises/exiges the effective area is dictated by the size of the inlet on the side.
As the hose is larger than that, you should end up with a lower pressure just behind the inlet than outside it which is good as it stops the system ‘rejecting’ air. Apart from that initial restriction it’s airbox shape and volume in the system that counts - a major plus point for the larger hose.
While I’ve never had one, the AutoTeknix airbox uses a 100mm diameter hose to good effect.
And btw-
Happy Birthday JFK…
Indeedy 
Happy Birthday JFK! 
Some good replies guys. I have the autotexnix air box with some 100mm pipe so it looks like a good set up from your answers. Now all I have to do is get the cold air feed to the air filter sorted out.
Next question is… would you take 100% of the air entering the engine bay from the N/S to feed the air filter or would you also allow some for engine bay cooling???
Wouldn’t take it all, unless you can do something to stop debris entering. Had mine connected directly with the motorsport connector and found holes in the foam filter together with lots of small grsvel in the hose.
I was looking at fitting a Pipercross Vemon/Viper if they do a 100mm inlet and outlet.
Has anyone ever fitted one before?
Looking forward to make it like tis:
http://octanereport.com/tuned-cars/2010/06/01/feature-lotus-exige-s1.html?pid=1978#imggallery