HP to Speed ?

[R.I.P.]

If you have a 200hp with a 28p prop turning 7000 with a 1.87 lu
What would a 250hp turn the same prop at the same rpm . what would the speed differance be or would they be the same? Does more hp mean anything if the prop is spinning the same rpm. Do you gain any speed from same rpm.?

[CSD23]

Same prop, rpm's, and lower gears should equal same speed. Difference would be in hull and slip. With more displacement and HP you should be able to turn a bigger wheel equaling more speed.

[R.I.P.]

I feel the same way but with a 200 running 7000 and a 28p how high can you go with a stock 200 before I snap a shaft. I will try a 30 et . but my phone gps said I was only doing around 70 mph ?
On the hydrostream that weighs 875lbs. I think it was more like 80. Any idea what would the rpm to speed should be. I see the guys on here with 280hp running a 32et. Thats why I cant see a stock motor turnning a 30p or more.

[Tague]

first thing to do is figure your slip numbers
formula
rpm/ratio*pitch/1056
7000/1.87*28/1056=99.25mph speed with 0 slip

if you were only going 70 your slip would be 29% 99.25*.71+=70.47mph
80mph would be 19% which in my opinion is more likely but still high.

as far as props go, it depends on your boat weight, hull design and setup. if you step up and run a 30 you may need to take some diameter out of it to turn it. My brothers Vicious STS that we built was 450lbs has a stock 200hp and now turns a 32 cleaver at 7000 at 99.4mph.

[R.I.P.]

I have a Hoss offshore cut nice prop. I was running a 26p chopper but when I switched lower units the 26 reved over 8k. Thats when I went with the 28 hoss. The set up is 6"back and 1" above pad.
Im trimed up all the way and the more I trim the higher dryer the boat rides. At full trim I have great water pressure and around 5500 im dry it will rev up to 7100 on a drift up and down from 6900. Gps is so slow to read speed by the time im up and running it jumps at 3 4 mph incraments. when at full speed I cant look down .

[transomstand]

but when I switched lower units the 26 reved over 8k.

Different gear, must be 2:1

[R.I.P.]

stock 91 200 lower w/nose cone. did they come with 2.1? How can I tell?
by the way its a solid hub. snaped my older lu shaft and replace the lu rebuilding old one for spare