hi jerry!
a few questions here that sort of depend on understanding a few other things first before the other can be properly understood. (did that sound right?), anyways, i know you have a good basic knowledge, so i will attempt to explain best i can. sometimes i even have to go over basics myself before i get a better understanding of what is going on. so will start with your last question first.
"The single phase motor uses 12 amps at 120 volt = 1440 watts. Why is the 3 phase concidered more eficient?"
ok. first, and this will be just a very basic way to look at it, a 1hp motor is 746 watts output. power consumption is 1440 watt
746 divded by 1440=.518 your motor is basically 51.8% efficient.
if you draw out a single phase sine wave, basicaly you have 2 power strokes if i may put it that way. one on the way up, and one on the way down. when the stroke stops to go the other way you basically have no power going on. this is between "cycles". the gap between one cycle and the next, basically have wasted space between them where there is nothing being accomplished. now if you are to draw in a second and 3rd sine wave between the power strokes of the single phase sign wave, you are now "more" efficiently making use of the available stator core. now, not quite exactly as i say it, but when 1 phase of the 3 is dead, you have something or quite a bit comming from the other 2 phases. a three phase machine output is always a combination of the total 3 phases combined. the same space in the core is utilized much better working between 3 phases rather than one. the 51.8% is a representation of how much output is derived from the input. material quality, design and mechanical losses all contribute to the actual efficiency.
next. the 3 phase 1hp motor. still 746 watts. it should be viewed as a single unit rather than 3 seperate phases as this is how it is designed and works. all 3 phases work together.
746 divided by 874=.853 your motor is basically 85.3% efficient
so now we have gone from a 1hp single phase @51.8% efficiency to a 3 phase 1 hp with 85.3% efficiency. this is the result of multiple phases working together.this is why 3 phase cores are smaller than 1 phase cores for the same given horsepower. you could view it as 1 man rowing a boat, he has to row like hell, and there is a "lag" between strokes. with 3 men rowing, while 1 is between strokes, the other is in full power stroke and the other is partially into the power stroke. the boat is moving further, easier, and more efficiently with less effort from the 3 men. basically, more efficient.
the difference you see between some motors amperage ratings may depend on the service factor, quality and design of the motor, or even if it has running capacitors which always stay in circuit on the start winding. these cpacitors serve to lower the start winding current draw and also to add to the total eff of the motor.
"Higher voltage in delta confuses me I thought star wasc higher voltage?"
lol, seems to be quite a bit of debate on the subject lately and i think quite a bit of misunderstanding from a few people also.
lets first speak about how it works on motors, and why it is used.
any motor can be designed and wound to work on star or delta connection. star connection is generally used on smaller motors and larger motors are usually based on delta. delta is often used in conjunction with star to aid in the starting of large high inrush current that they demand during start up and as a means of creating what is known as a "soft start". a soft start demands less current draw and also reduces much of the harder mechanical load on equipment during the starting transition to full speed. by having a star delta start motor, the inrush is reduced because the phase in star, only "sees" 58% of the line supply voltage. when the motor is up to approx 75% speed, the motor contactors change over to connect the phases in delta, and now allow the phases to "see" 100% of the supply voltage. this creates the soft start.
if you draw out 3 phases in the delta configuration, you can see that each phase is connected to 2 power lines. this is where the phase sees 100% of the supply voltage. if you draw out 3 phases in the star connection, you can see that each phase receives voltage from 1 power lead and from the end of another phase. now the phase only sees 58% of the supply voltage. that 58% figure is a most valuable tool for anyone to remember. it is the basis for much design work.
now to speak of star/delta in the use of wind alternators.
for easy understanding and to explain what i mean, lets use a total of 100 turns for a phase and 12 volts as a number to work from.
with the alternator up to cut in speed, we are seeing 12 volts. the 12 volts is derived and measured from 2 of the three power lines. it is also being derived from the combination of 2 phases. if the same winding was connected in delta and at the same rpm as star, we would see 58 volts measured between any 2 of the 3 power lines, because the voltage is only being derived from 1 phase. refer to a delta diagram to fully see and understand this.
to make the alternator put out the same 12 volts and at the same speed, you would have to take the 100 turns in that phase and multiply it by 1.73. so now we have 173 turns in the phase to give you the same voltage as star at the same speed. 1.73 is just the inverse of 58%.
if we take an alternator that puts out 12 volt at 200 rpm connected in star, and wanted to connect it in delta and get 12 volt, we would have to take the 200 rpm and multiply it 1.73 200 x 1.73=346 rpm. this is the basis and use of a star/delta switch for genny use.
a genny connected in star will give you cut in at whatever rpm you design it for. as rpm builds after cut in, it will get to the point that the prop may wish to stall. when this situation is happening or just before, a installed star/delta switch will kick in to delta. when it goes to delta, it drops the voltage of the 3 phase and also drops the current. it then allows the prop to gain more speed and gain more avaiable watts. basically, it allows the prop to get ahead of the genny rather than the prop starting to lag behind the genny which causes the stall. i am just getting into this a bit as it may give some of the others new to this genny building stuff a better idea as to what is actually taking place. the stall problem can be overcome from simply using a larger prop, but the ideal situation is not to my knowledge. a smaller prop can be used with a star delta switch and reap the benefits of both low and higher speed wind.
a genny designed to operate only on star or only on delta and at the same given cut in rpm, will really not benefit one way or the other. apparently some dual rotor coreless units have less problems from parasitic losses using the star connetion as apposed to the delta connection. i cannot comment on thsi as i have never completed a coreless dual rotor genny.
sorry to have babbled on too long jerry, but this is just how i like to explain things. hope this is what you were looking to have explained. this is how i view it.
by the way! i just installed a star/delta switch on my 1.5hp conversion. the only thing that controls it is the wind blowing by a pipe that creates vacumm that in turn controls a vacumm switch with a normaly closed and normally open set of contacts. the switch then controls 2 3 pole contactors that change the genny from star to delta. it is totally self powered from the ac side of the genny. so far, seems to be extremely promising. i will post on it when i have more data. i am a bit electronic parts building "challenged" this works for me 
really appreciate and enjoy the sharing of your experiments.
have fun!!!!
zubbly
