If I'm using a 305 ... which heads are better.... 350 heads for flow, or 305 heads for compression. they would both be ported and have valve jobs w/ 1.94 int and 1.6 exhaust... would the increase power from flow equal a drop in compression (therefore a drop in HP).... OR would the increased compression (from the 305 heads) add MORE power... which would be more economic... THANKS IN ADVANCE

 

Once upgraded with larger valves and ported, a factory 305 head flows as good or better than a factory 350 head.
(with the same valve size and porting)
The difference in the two heads is the valve size and the combustion chamber size. The ports are essentually the same.

Both heads suck in stock condition and both can be improved
to about the same level.

So for a 305 you'd really want to start with a 305(HO/TPI) head
because of it's smaller chamber.

 

Whats casting number heads are you thinking of using. But really you want the greater compression around 9:1-9.5:1.

 

What would I need to do to get good compression... I'm using stock pistons, With molly rings, does the head gasket make a difference ??? what about shaving the heads ???? what is the highest compression that you can use PUMP GAS (the cheapist stuff for ) ???

 

If you want to have a motor that will operate properly on cheap
87 octane gas than do not raise the compression ratio (much).
Yes the head gasket makes a difference. A thinner head gasket
will raise compression compared to a thicker head gasket.
Be aware that most stock motors already came with a thin head gasket.

The absolute maximum compression ratio that a said motor will tolerate on a certain octane fuel, is not absolutely knowable.
There are too many other factors.

The overall design and running environment needs to be qualified.
Having a little less compression (than absolute) is better than having too much. An engine that detonates and knocks will be down on power and will have a short life.

The first thing to do is to accuratly deturmine tha actual
compression ratio of the motor parts you have now, how your going to modify it etc and then I or someone can advise you on a
compression ratio to build for and how to get it.
Need to know more about your combination and plans.