large inlet valve size vs small port?

[ampor]

Hello

Trying to learn a bit more about head flow, and wondering what is the effect of installing a larger intake valve without enlarging the port. I'm aware of previous info posted here about having the valve throat end up at 86-88% of the inlet valve diameter, but what happens if there are constraints that prevent opening the throat? What to expect if your valve throat is only 80% of inlet valve?

Thanks

[ampor]

"You should be able to answer this for yourself. A bigger valve will show flow advantages at low and medium lift up until the point at which the port size becomes the limiting factor but you can't get more peak flow than the port will supply regardless of how big the valve is so there's not much point fitting big valves if you can't also size the ports to suit."

I knew an unchanged port would limit peak flow and higher rpm power; what I didn't know was how the larger valve would affect flow and pressure recovery and possibly reduce torque. I have never seen a back to back test on a mod like this. I'm looking to increase torque as much as possible under 3500 rpms. We have an old, heavy van that is underpowered, and we're looking to boost torque at cruising speed which is typically 3K rpm.

Looks like I'll give it a try, thanks for the answer.

[ampor]

Stan said: "If your head has some kind of valve lift limit and flows less at max valve lift than with the valve installed upside down. You might try seeing what a larger valve will do."

Don't quite know what you're saying here.

We don't want to change the cam, or increase the engine size. Just looking for a low budget band aid for our old van.

Thanks