[steve25]

A lot of what’s needed for a intake to exh ratio is in part put in place actually by the motors compression ratio.

Once you get up to the 10 to 11 to 1 range, a over all 75% ratio is all that’s needed most times.

Please note like I just posted this is the over all ratio by averaging your numbers in the range of valve lift you will have.

Above 11 to 1 in what we will assume is a race only motor a number of 65% works.
As you drop down below 10 to 1 there is still a lot of unused gases left in the bore once the piston has dropped down to BDC.

In these cases and especially if exh manifolds are used you want the valve job , the valve and the valve bowl shape to produce the highest amount of LOW lift flow that can be had.

This is where flow testing is indispensable unless you really have a good grasp on what your looking at from many years of porting work under your belt .

This will blow down the cylinder faster and take good advantage of doing that at a time when the exh runner is not saturated with the gases due to the rising piston.

In other words get a lot of the needed job done before the piston even starts the exh stroke cycle.

Dropping this gas pressure as fast as possible also means the other moving pistons are not using as much of there motion energy to pump out these gases in other cylinders when exh stroke does start.

I dont know, that’s the best I can explain it right off the top of my head.