when I first replied...I worked on 750cfm = 1.2psi.....that's not correct.
750cfm 20"WG gain is atmospheric intake/snorkle conditions, in this CAC situation we are talking boosted conditions at 20psi (62mm SC pulley).
Hence the volume through the cooler is significantly less.

I picked this up beacuse I was getting 8rwhp from the DCAI from needswings figures, but only getting 1.2psi but only a 6wrhp gain from the CAC clean.
I had a bit of a think and worked out that's because at redline (6000rpm for simplicity) the engine is consuming 370cfm - that is the number (slightl larger due to some dP) flowing through the CAC (charge air cooler to be precise) to the engine.
In that case the 4"WG converts into (370/250)^2 x 4" = 9"WG

But needless to say - if the needswings intake can give you 8rwhp and people's "seat of the pants dyno" senses a significant gain there....there is every reason to chase the 6rwhp gain to be had on the offing with a good CAC clean....lets get on it!

Wood - sorry to hyjack...all related.