gutting out the manifold or not, i still think you are loosing way too much air velocity with a larger tb. 70mm is probably too much for even the 3L, but like mark(mistergrym) said 73 would be ideal for the vortech. in size vs. velocity there is a peak point at which velocity is greatest, and an increase in size will cause a loss in velocity. Just think of it this way, if mcdonalds gave you a straw or a 4 inch (diamete) pipe, which do you think you could get more coke through in the same amount of time? The straw, you probably couldn't even the the coke to your mouth with the pipe, it is the same principal with your car's engine. Now if you hooked a blower to the bottom of your coke cup then the straw becomes a bottle neck and the 4 inch pipe becomes more ideal. just some food for thought... hehe
