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Turbo charged rotary???

Posted: Wed Apr 15, 2015 8:58 pm
by Rotaryturbo
Hey guys my buddy posted a thread earlier about rotarys and I just figured I'd create my own account. So here's a little background, I've been around rotarys all my life and my dad drag raced them. I know them pretty well, and we know how to make power in a car I know nothing about putting one in a boat. My plan is to build a street ported 13b with an 80mm turbo should make around 600hp and 420 ft lbs of torque. I know that my max torque is between 7200 and 7500 it'll keep making more power the higher I go with the Rpms but the torque starts falling off. I have several questions what gearbox ratio should I use? I will be having a engine plate made up so I can pretty much bolt to any gearbox I think. I'm also limited to 68" for my prop. What's the best way to get this thing moving?

Re: Turbo charged rotary???

Posted: Wed Apr 15, 2015 9:02 pm
by yobee
I know some guys that build rotary cars too. My old boss works on the mech tech car. Those things can be built pretty bada$$

Re: Turbo charged rotary???

Posted: Wed Apr 15, 2015 9:07 pm
by Rotaryturbo
Yeah man I know about that car it's a 3 rotor rx8 it's sick. 6.19 at 230!

Re: Turbo charged rotary???

Posted: Wed Apr 15, 2015 9:22 pm
by aherr520
zoomzoom can tell you more regarding gear reduction but I think his is 3:1

Re: Turbo charged rotary???

Posted: Thu Apr 16, 2015 1:58 am
by OneBFC
If it keeps making more power and is still reliable at the higher revs, run it there. Match reduction required to the prop you want to run. Available props range from 2000 to 3200 rpm with the slower props being quieter.

8500 rpm with a 4:1 would turn a big blade.

Of course fuel economy won't be something you should worry about because it will not be so hot.

The thing will go like mad though! Would love to see it some time in the future.

Good luck!

Re: Turbo charged rotary???

Posted: Thu Apr 16, 2015 6:55 am
by Deano
I mostly agree, but I don't know that I would see the need to spin as much as Russ has proposed.
I guess that would depend on the intended use and/or the expected longevity, though.

In any case . . .
Be aware on the front side though that most props, especially the wide blades, aren't going to fit in a 68" space.
Generally 68" props aren't designed to, or come out of the box to handle that kind of hp.

Not that it couldn't be done, but it is something to give more than passive consideration to on the front side.
You will not be able to simply cut 6" off of a blade that would typically be used in such an application.

It would seem to me that a bigger cage would be justified for such an endeavor.

Re: Turbo charged rotary???

Posted: Thu Apr 16, 2015 8:08 am
by WaterWalker
Rotary:

At a 68 " Diameter disc area computing 25.32 square feet, you are limited to about 260 HP for efficient transfer of rotational HP to thrust. For better understanding, you would readily agree that say a 36" prop wouldn't do you very well or a 24" one even less. So, 68" 'ain't' enough for 600 HP.

David Wine

Re: Turbo charged rotary???

Posted: Thu Apr 16, 2015 8:37 am
by Deano
Well, I had the right idea . . . almost. :lol:
I was thinking maybe a whole herd of skinny blades might work, but I guess not.

That's good information, David. Thanks again for chiming in with real world data. :thumbleft:

Our little hull that we call 'the runt', only fits a 68" prop and would be way beyond a handful with 260 hp. :shock:

Re: Turbo charged rotary???

Posted: Thu Apr 16, 2015 5:42 pm
by ptr34
you need at least a 74" to 78" prop. and it can hold 600 hp back. run a 2.9 to 1 box @ 7400.. prop rpm will be 2569. that should work good. or 2.55 @7400 be 2900 prop rpms. We are building a 2.4 ecotec that makes 600 plus hp with a 2.38 75"8 blade saber. its for racing

Re: Turbo charged rotary???

Posted: Thu Apr 16, 2015 9:08 pm
by WaterWalker
ptr34 wrote:you need at least a 74" to 78" prop. and it can hold 600 hp back. run a 2.9 to 1 box @ 7400.. prop rpm will be 2569. that should work good. or 2.55 @7400 be 2900 prop rpms. We are building a 2.4 ecotec that makes 600 plus hp with a 2.38 75"8 blade saber. its for racing
Sure, 'hold back 600 HP." but do you want to get your full (paid for in fuel burn) thrust for that HP? Go ahead and set your pitch to some obscene positive pitch angle on your 74 inch prop and fan the air into a swirl instead of thrust? you will also feel it in the boat's torque roll.

The Signature 72 inch diameter three blade propeller has demonstrated 1200 lbs. of static thrust at 2800 RPMs with a 300 HP Lycoming engine. (that's history) that also computes to 10.31 Horsepower per square foot of propeller disc area while delivering four pounds of thrust per HP.

Providing 10.31 HP per sq. ft. of disc area for 600 HP would require a propeller having 8.6 feet or 103 inches diameter to get approximately 2400 lbs. of thrust! etc.

When you get your 600 HP boat all set up with a 74" prop with enough pitch set in to 'hold 600 HP back', put some scales behind it and measure the results as maximum static thrust! I would be surprised to see more than 1500 or 1600 lbs. of thrust.

David

Re: Turbo charged rotary???

Posted: Thu Apr 16, 2015 9:22 pm
by ptr34
Trust me I wouldnt have any problems. I got best prop on the market on it

Re: Turbo charged rotary???

Posted: Fri Apr 17, 2015 11:19 am
by Rotaryturbo
Thanks guys for the input I'm still trying to learn this stuff. I understand that I'll have to use a bigger prop but in regards to the thrust are you guys saying that the motor will not have enough torque to push the boat? I'm not trying to make a race boat I just want something that'll I'll enjoy and is different from what's out there. All advice is appreciated.

Re: Turbo charged rotary???

Posted: Fri Apr 17, 2015 11:20 am
by ptr34
No I'm saying on a lite boat with a short prop with right gear. It will run everywhere u want it too

Re: Turbo charged rotary???

Posted: Fri Apr 17, 2015 11:43 am
by Deano
Rotaryturbo wrote:Thanks guys for the input I'm still trying to learn this stuff. I understand that I'll have to use a bigger prop but in regards to the thrust are you guys saying that the motor will not have enough torque to push the boat? I'm not trying to make a race boat I just want something that'll I'll enjoy and is different from what's out there. All advice is appreciated.
The quandary arose only because of your specifying a 68" length prop . . . no other reason.

Typically that much horsepower would be coupled to a 80"-84" prop.
This is done in order to gain all available efficiency (maximum thrust), in spite of the laws of physics. :salute:
Other things being equal, diameter trumps pitch. Did you ever see a cargo helicopter with a 6' rotor?

As Terry pointed out, with the right gearing to attain the correct prop RPMs, you will be fine.
You will just need to be using more prop than the 68" that my antique 4 cylinder Lycoming uses.

Re: Turbo charged rotary???

Posted: Sat Apr 18, 2015 11:50 am
by ZoomZoom
If you will PM me I will give you my ph. # I have been running 13B's now on my boats for 15 yrs with my Bell-47 gearbox which is (1to 3.17 ratio) I may be able to help you with some info, and some things not to do. Zoom Zoom

Re: Turbo charged rotary???

Posted: Sat Apr 18, 2015 3:03 pm
by Joe863
Take Zoom up on that offer!