150 vs 160 hp

ScottK

ScottK

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ScottK
Would there be a noticeable difference other than speed between the two engines in a 172?
 
Depends, what do the individual planes weigh, what mods were done, climb or cruise props, etc.
 
160 hp will give higher climb rate, not much speed. Horse power=Climb rate, aerodynamics=speed
 
c177tx said:
160 hp will give higher climb rate, not much speed. Horse power=Climb rate, aerodynamics=speed
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Maybe

10hp will be overcome with a good STOL kit, climb vs cruise prop, or a lighter plane.
 
I bet you would notice it, that's a 7 percent increase in power.. not insignificant. The cruise speeds will likely be very similar, or at least not noticesably different, but the climb rate would be noticeable. I am always amazed at how much of a difference I get in climb performance between the 160 hp Skyhawks vs the ones with the 180 conversion

c177tx said:
160 hp will give higher climb rate, not much speed. Horse power=Climb rate, aerodynamics=speed
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Yup.. that's very similar to what someone else told me. I feel like with any fixed pitch prop there's always a compromise somewhere. Surprised actually that not everything is CS. Imagine having a car with one gear... super sluggish to get moving, then maxes out somewhere at 50 mph. No thanks.
 
New high compression cylinders usually add more than 10hp to a used 0-320. In the Cub world there's no question the extra 10hp is beneficial. It would be in a 172 as well, especially at heavier operating weights.
 
150 hp 172 at Boulder in July = very long taxi prior to rotation.
160 hp 172 at Boulder in July = almost as long but not quite...
 
In the switch from 150 hp (172M) to 160 hp (172N), same gross weight, Cessna claimed improvement in takeoff over 50-ft obstacle, from 1525 ft to 1440 ft, and improvement in best rate of climb from 645 fpm to 770 fpm. Book service ceiling went up from 13,100' to 14,200'. They also claimed a 7-knot increase in cruise speed, but no increase in top speed. But ...

Screen Shot 2017-07-10 at 11.44.59 AM.png

... take all that with a grain or two of salt. Those numbers came from brand-new, perfectly-rigged airplanes with strong, new engines, and flown by professional test pilots.

In the real world you'll notice somewhat better takeoff and climb performance and ability to get to higher altitudes, and little if any change in cruise performance. One nice thing is that you can climb at a higher airspeed and still get a reasonable rate of climb. That helps keep the engine cool.
 
Flown both and I have never found any significant increase in performance. The 160hp might be a knot or two faster with a better climb, but that's probably just in your head. :)

The 172 is a fairly draggy airframe in general, so 10hp is not going to make a huge difference.
 
That's why the Hawk XP was so popular, because horsepower doesn't matter? The difference in a stock XP at 195hp and the Isham STC at 210hp? Absolutely worth it. 150 to 160 is no different.
 
Stewartb said:
That's why the Hawk XP was so popular, because horsepower doesn't matter? The difference in a stock XP at 195hp and the Isham STC at 210hp? Absolutely worth it. 150 to 160 is no different.
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Isn't the stock XP max cruise power 80% while the Isham STC 75%?

80% of 195 = 156
75% of 210 = 157.5
 
asicer said:
Isn't the stock XP max cruise power 80% while the Isham STC 75%?

80% of 195 = 156
75% of 210 = 157.5
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Yep ... the French-built FR172 Reims Rocket was sold with the full 210 hp (at 2800 rpm), just like the T-41B, since 1968. The otherwise-identical US-market R172K Hawk XP was introduced for 1977, to take the place of the moribund Cardinal in the catalog, with the engine limited to 2600 rpm (195 hp) -- solely for noise reduction.

The engine was built to cruise at 157 hp or thereabouts anyway, so they just fiddled with the arithmetic and defined cruise power as "80%".

The Isham STC just brings the R172K back to Reims Rocket standards.
 
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I figured the <200 was a high performance endorsement thing. The standard 76" prop wasn't loud and even the 80" seaplne prop wasn't very loud with or without the Isham mod.
 
Whatever. I had one for a few years. PK B2300 floats, 80" prop, Isham. My best friend bought one and added the Isham kit, then got an approval to add a seaplane prop on tires (I had that one, too). Fun airplanes!
 
On my little airplane of 38 HP. I upgraded the engine to around 42 hp. What did it give me. A little more climb and the chance to spend more money on a new prop to remove the extra RPM's that came from the extra HP. But it does climb a lot better. Cruise speed may have increased about 4-5 mph.

Tony
 
Tantalum said:
I bet you would notice it, that's a 7 percent increase in power.. not insignificant. The cruise speeds will likely be very similar, or at least not noticesably different, but the climb rate would be noticeable. I am always amazed at how much of a difference I get in climb performance between the 160 hp Skyhawks vs the ones with the 180 conversion
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The answer lies in two important words in aviation (especially in ME airplanes): "Excessive horsepower".
It is not only for ME pilots. Us SE guys can use the knowledge as well.
 
Enough to notice, but not enough to matter too much. More in climb than speed.
 
Stewartb said:
That's why the Hawk XP was so popular, because horsepower doesn't matter? The difference in a stock XP at 195hp and the Isham STC at 210hp? Absolutely worth it. 150 to 160 is no different.
Click to expand...

I once flew a XP with the Isham on amphib floats. It seemed to have pretty good performance getting off the water and climbing out.
 
Why not spend the money on a power flow exhaust instead and get 17 hp instead of 10?
 
In theory, cruise increases proportionally as the square root of the thrust increase or cube root of power increase. Therefore, adding a mere 10 horsepower won't buy you much additional speed (maybe about three knots - (160/150)^(1/3)*120 ~= 122.61) regardless of what cessna marketing might otherwise suggest.

That climb improvement though...
 
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