higher comp. = more hp............but yea youll end up of havin to use a better grade of fuel.

 

Compression is NOT the only factor in making more power. If You lose airflow numbers while gaining compression, You will lose power. No rocket science here. Airflow makes horsepower because an engine is an airpump.

 

whats compression have to do with airflow?...its not like your changin to a smaller carb. or puttin a restriction in the intake. NOW if you say the 305 heads have smaller intake ports,or something along those lines, then yea youll lose airflow...

 

The 305 heads have a much smaller valve size than the 350 heads. There's alot of lost room on the combustion chamber when stepping down from a 4.000 bore head to one designed for a 3.750 bore. That's one of the biggest reasons for the 305 being considered a boat anchor by most people. You'll be losing significant airflow numbers, stick with heads designed for the 350, and see how far you can have them milled without having valve clearance issues.

 

compression wont hurt airflow. Valve size will

 

This is a liltle long winded, but has a lot of good info in the various Vortec heads from GM.
http://www.popularhotrodding.com/eng...0511em_vortec/