I had a thought about how to tell where the bottleneck is on the intake side of any engine. Given the nature of the log head on the sbf6, there are questions as to how much value a larger carb or larger valves realy make. While what I am suggesting is not going to give you HP or torque numbers, it may help find where to spend your time and money for the best effect. The one thing I think everyone would agree on is that vacuum at WOT is a BAD thing. At least you want to keep it to a minimum. The trick is to find out where the most vacuum exist in the intake track and at what RPM. It seems to me there are several places that you would want to measure. The most obvious would be just under the carb. The next would be just outside each valve or as close as you can reasonably get. You could baseline an engine by measuring vacuum at these points with various RPM. If you improve flow down stream of the measuring point, you should see an increase in vacuum. For instance. You measure X inches of vacuum at 3000 rpm baseline. You add larger valves and do some light port and bowl work. You should be able to see X+ vacuum at the port and at the carb because you increased flow away from the measuring point. The reason for a measurment at each port is to figure out if there is 1 or more cylinders that are better or worse than the others. This would let you know which cylinder to check for additional porting, cam wear, valve adjustment, etc. If you add a larger carb(upsteam of all measure points), the vacuum level should decrease. With this you could see if the additional CFM were being used and at what RPM it was really making a difference. Of course you could also do this on the exhast side, but measuring the pressures at the high temperature would take more money than adding vacuum take offs and buying a vacuum guage.