1. Why do you think you will get increased flow installing those valves upside down?

2. What do you want to accomplish by drilling out the port? That is, what flow rate do you think you need for a shower that you can't get with an unmodified valve? And which port are you thinking about trying this on? Do you have a giant water heater that won't start running out of hot water if you have many GPM of water flowing?

the rite-temp valves have a higher flow rate to the tub than the shower, so I install them tub side up

I understand what you're on about. I've had the same idea with a Moen valve I purchased but have not yet installed. But I was going to install it the normal way and simply pipe the tub outlet to the shower head and cap off the shower outlet. I've never done this, however.

Scott-

Thanks for clarifying that. I agree with weedmeister about installing normally and piping up to the shower. I'm still curious: why do you want such a high flow rate for a shower? Multiple heads?

the rite temp valves are easily reversed. 2.5 gpm is not much flow-especially to a rain shower head

Isn't your rain head restricted to 2.5 gpm ?

If that's the case , it doesn't matter how much your valve will output.

I am using antique-vintage shower heads that are not restricted

Your not going to get 10gpm from any showerhead, the water saving showerheads achieve 1.5 gpm and feel the same. Standard shower heads are 2.5 gpm as xedos mentioned. The fact that you want to waste that much water in the first place is disheartening. Do you realize that water is the most important thing we have? What would you do if you turned on the tap and nothing came out? Don't waste water just to waste it. I dont live in California, but eventually their water will run out and there will be a mass exodus. Just wait and see.

Install it correctly, the tub side down, so when someone wants to fill the tub it can fill faster as designed to. The reason the shower doesnt get as much flow is because it is not needed.

I'm on a well and septic near the rainforest. Where do you think that water is going to go? Maybe if I turned on a sprinkler and watered some grass I could make it disappear.

Those antique heads prob are 5-6 GPM , depending on how vintage they are.