390 vs 408

I dont think there is any documented numbers. I do have experience flowing heads on a flow bench. Let me give you a little background. When someone flows a head on a flow bench, we use a bore plate that simulates the bore in an engine. Lets take a big block chevy for instance. Typical 454 bore is 4.280 and when heads are flowed for advertisement purposes they flow them with a 4.500 bore. Now I know that it is a .220" difference but its a good illistration. There is typically a 10% difference between the 2. I know that when I flowed my edelbrock RPMs on a bench they flowed 220 cfm, well below what they advertise. That was with a 4.030 bore. I figure Edelbrock flows them with a 4.100 bore which is .070 bigger and their numbers come in at 250 cfm. This is just speculation on my part and I have not confirmed this with Edelbrock. So if you take the cfm results and times them by 2 to get a theoretical hp potential for a given engine, I would lose out on 60 hp. 60 hp is a lot to lose to a smaller bore. I know that some of the guys here are running 390's and they are getting quite defensive about it. I have never said a 318 is a boat anchor, as a matter of fact I have support you guys and I believe that your 390s run hard! So please just take this as an information source for our friend across the pond can take into consideration for his personal car. All cars are different and our expectations are different so everyone needs to find a combo that they like. I have read every word that is on this thread and it doesnt change what I am saying or my opinion and this is just what it is, an opinion. Go back and read my posts and it may change how you feel.