340 camshaft
Small Block Head Flow Chart
That will narrow it down considerably.
The unported large valve factory head numbers that have been posted all look something like this.
This shows that opening the intake valve .3" allows 157 cfm to flow through on the bench.
Opening it .4 inches allows 193 cfm to flow through. Wow - big gain.
Opening it .5 inches only gains 7 cfm more.
And over .5 gains nothing.
So for this head, there is little point in looking at cams that open the valve more than .5 inches. Somewhere between .4 and .5 there's diminishing returns for increased opening.
Yes head flow can be improved. But its important to do so without losing velocity. If the air flow at low throttle openings slows down, fuel can drop out and the quality of the fuel air mix in the chamber will suffer.
Figure out what you have.
Then see what will work nicely for what you want to do.
Only if nothing reasonable can be found does it make sense to spend time and money on more modifications.
Which is why it makes sense to cc your heads, measure the cc in the hole or height above deck of your pistons, and think about the gearing you will want for the driving you'll be doing. Finally, take a good look at what your heads will do. Hard to find a shop with a bench but this thread will ballpark the situation.
Small Block Head Flow Chart
That will narrow it down considerably.
The unported large valve factory head numbers that have been posted all look something like this.
This shows that opening the intake valve .3" allows 157 cfm to flow through on the bench.
Opening it .4 inches allows 193 cfm to flow through. Wow - big gain.
Opening it .5 inches only gains 7 cfm more.
And over .5 gains nothing.
So for this head, there is little point in looking at cams that open the valve more than .5 inches. Somewhere between .4 and .5 there's diminishing returns for increased opening.
Yes head flow can be improved. But its important to do so without losing velocity. If the air flow at low throttle openings slows down, fuel can drop out and the quality of the fuel air mix in the chamber will suffer.
Figure out what you have.
Then see what will work nicely for what you want to do.
Only if nothing reasonable can be found does it make sense to spend time and money on more modifications.
