# Question of the day: Engine with the highest power/weight ratio? (Hint)

This engine produces in excess of 96 hp/lb.

That is not a misprint. Take the # of hp it produces, divide it by the # of pounds it weighs, and you'll get a number that's a little over 96.

1. Maurits says:

I’m guessing it’s something really light.  Do biological entities count?

2. Erik says:

THE HEART!

3. Wolf Logan says:

My first thought was the Bugatti Veyron, whose engine puts out over 1000HP. But as that engine weighs more than 10 pounds, it’s off the list. The micro Wankel that Raj linked yesterday looks promising, but I don’t know how much it weighs (since as far as I can tell it’s never been fabricated).

The Veyron was designed to extract just about all the power available from a car-sized gasoline-burning Otto-cycle design, so it’s unlikely that any other Ottos would surpass its power/weight. Wankels and 2-strokes have better ratios, but even then it seems that you’re just not going to get that kind of output from gasoline. So I’m guessing now that it’s going to be fueled by something besides gasoline, and probably use a continuous drive design (like a turbine or a Wankel). And now I’m not going to be able to stop thinking about and researching this…

4. just a completely wild guess, but what about a hard drive’s motor ?

5. Maurits says:

> hard drive’s motor

Sounds likely to me.  An electric motor will output power proportional to the square of its dimension, but will have a mass proportional to the cube of its dimension… so making everything smaller will increase the hp/lb ratio.  Is there anything smaller?

6. Wolf Logan says:

ericgu has already verified that the engine in question isn’t an electric motor, so we’ve got to guess again.

7. Maurits says:

Well, this model airplane engine has 18 hp/lb:

http://www.justengines.unseen.org/moki210.htm

so it’s got to be about 1/5 the size of that.

This guy builds really tiny engines:

http://www.minimodelengines.com/

but he doesn’t give power or weight figures on them.

8. Maurits says:

Er, never mind, that model airplane engine isn’t 110g, it’s 44.7 oz.

Helicopter engines have a power-to-weight ratio of about .1 hp/lb.  Model helicopter engines like http://www.justengines.unseen.org/ASP36r.htm get this up to about 2 hp/lb.  But 96 hp/lb?  That’s got to be REALLY small.

9. Maurits says:

OK, I think I got it.  It’s a model turbine engine.

"I know the professionals can get 100 HP/lb and more"

Model jets, huh?  Scary.

10. Mintaka says:

How about a rocket engine? They’re not so heavy (if you don’t include the fuel) and they prodce a LOT of power.

11. Keith says:

Space Shuttle main engine

12. Keith says:

or more specifically, SSME Turbopump

13. Keith says:
14. Wolf Logan says:

So what powers the SSME fuel turbopump?

15. Jim Argeropoulos says:

I don’t think it is a rocket because Eric said it has to have a shaft.

Despite the cool factor of the 6 cycle engine http://www.autoweek.com/apps/pbcs.dll/article?AID=/20060227/FREE/302270007/1023/THISWEEKSISSUE I don’t think it is this either.

16. Herb Warren says:

The engine used in the SR71 has to come close.

http://www.wpafb.af.mil/museum/engines/eng55.htm

6000 lbs, but 32,500 lbs of thrust. Hard to convert to horsepower though. You’d have to know torque at rpm specs.

17. Maurits says:

http://cpl.usc.edu/eschuste/turbine.htm

Weight: 6.5 oz

Thrust: 4 Pounds