ORIGINAL: ukrconsul
It is not so difficult. The engines and motors are easy to compare.
Four stroke 90 size – 1.7 HP – 1.7X 750 = 1275 W
We need motor that has the same power.
read Matts first reply... it it more difficult than that...
give me 1700watts and I´ll return 300oz of thrust and 55mph to you... a 91 can not do that. I choose to spin a 20x10 instead of a puny 14x7, which makes the electric setup way more efficiant.
I found it more to be like you need 1.5times the glow hp to equal an "electric horsepower", (I know what a horse power is but you get the picture...)
so 0.67*1250 ~ 850watts, put 850 watts through a 8.8oz Hacker B50 and you get 160oz thrust and 50mph, more like the .91 4stroke...
again, this is only a rule of thumb it does not apply to all setups, but for properly geard motors it is a hint to the right direction