I assume you are talking about this ship.

http://www.parkzone.com/Products/Default.aspx?ProdID=PKZ1880
Are you aware of this predictive on line program?

https://www.ecalc.ch/motorcalc.php
I might be mis-understanding Hai-Lee, but as a general rule the last 20% of the blade produces 80% of the thrust, this is regardless of the rotational speed of the propeller.

Thrust is just how fast you can move a certain amount of air, mass times acceleration. With propellers you can get the same thrust moving a little air fast or a lot of air slowly.

I assume your motor is around 1100KV so with a 3cell and an 8” pitch your pitch speed will be about 80mph max.. Then you'll have to factor in the airframe drag and I suspect your top speed in level flight will be around 65 mph to 70 mph.

Here is a simple formula to help you see some of the basic relationships of the propeller to power.

Power = K x P x D^2 xRPM^3

“K" is a constant that addresses things like air density, blade shape, number of blades etc. More advanced formulas can extract these variables out, but for our simple 2 bladed props a “K” factor of 1.11 to 1.31 works.

But what I’m trying to show is the relationship of the major propeller parameters. Notice that power is a square function of the diameter and a cubic function of RPM. This means that it takes a lot of power to spin a propeller just a little faster. And as Speed (pitch speed) is just “P” times RPM you need to cut down on the prop’s diameter if you want to increase the pitch speed and still stay within the power rating of the motor and ESC.

On the subject of speed are you aware that the drag on the airframe goes up by the cube of the airframe’s speed? So to go twice as fast requirers eight times the power!

I fear that turning an 8x8 prop with a 1100 KV motor on 3 cells is taxing your stock 18 amp ESC. As it looks like the motor will be drawing close to 20 amps.

A note on speed. It really is boring to just go fast. I know as I use to make engines for, and race, FAI F3D Pylon. The skill and fun of RC flying is putting the aircraft where you want it.

To go around 100mph plus on an 8x8 prop I need to use something like this.

http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFL4205
http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLM4025B
http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLB25004S30
http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLA1060B
I hope this helps.

All the best,

Konrad

P.S.

Sorry I see you are not using a stock set up (4cell). As Craft Dan is saying it can be trouble. But for ROG flights a stalled prop isn't too much of a concern. Even if you lift off before the prop is fully hooked up you will still have enough thrust to over come the airframe drag at these low speed. Just don't expect the best climb rate. On most Pylon racers the prop doesn't hook up until long past the first pylon.