What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

150 vs 160 performance diff?

sbalmos

Well Known Member
So I've got an IO-320-E1A (thus a 150hp model) on my 9A, spinning a Catto 67x71 3-blade. Perfectly happy with it, typically doing 140 KTAS at 2350-2400 RPM. For curiosity, a few weeks back I did a WOT run at 8000ft to see what my top end is. Looks like my max is 155 KTAS spinning 2650 RPM.

I have read in the archives that the 150/160hp performance difference is "huge" (for various perceptions of "huge"). So again just for curiosity, I'm wondering what that new top end and cruise would be?

How much is the 10hp penalty?
 
Any significant improvement you will see will be in take-off and climb. You will notice VERY little improvement in cruise speed.
The delta between hp vs. cruise speed is not linear.
 
Noted Mel. With the 150 and the Catto, it already climbs like a banshee. I've, at times, seen people mention cruise maxes in the 160s or so. Was just curious. Call it repressed jealousy. :p
 
Not a huge difference between 150 and 160hp.

My top end at 8K is about 165KTAS, but I'm spinning a fixed catto at 2750rpm rather than your 2650, so it's a bit apples and oranges. Besides, I never fly at that airspeed except for test purposes. My 65% economy cruise is about 146KTAS low alt and about 150KTAS at or above 10K. (For my carb'd/magneto-driven 320, that 65% results in about 7gph on the fuel flow.)
 
+1 with Steve on 160HP

My numbers are very similar to Steve’s numbers between 165kt and 167kt true at 8000ft DA, 2700RPM, WOT, but NOT leaned for best power. I would over speed with leaning. I see similar cruise numbers although I’m not picky, I set where the ellison wants to be that day, and lean it way out. I tend to see an extra couple knots /tens of RPM with the EI extra LOP advance in the CPI2. 160hp O320H2, ellison and EI, Sensenich FPGA. When I ran the Sensenich aluminum, it actually wasn’t any different. I’m intentionally a little underpitched on the GA for climb performance at 4.5 and I really like how it’s set up.
 
Last edited:
I just did a speed run and found at 8000' I'm able to get 2670 RPM and 160 Kts out of my 160 HP engine. At 7500' I could get 2690 RPM and 162 Kts. I have the Sensenich Ground Adjustable prop at setting #5. I could probably go down to setting #4 and hit 2700 RPM. The top speed I've seen at 2700 RPM is right around 163 Kts. I usually go LOP and cruise at 147 Kts WOT at 2470 RPM, which seems to be the sweet spot for my RV-9A.
 
Any significant improvement you will see will be in take-off and climb. You will notice VERY little improvement in cruise speed.
The delta between hp vs. cruise speed is not linear.

Absolutely correct regarding speed. When it comes to climb, ROC is linearly related to Excess horsepower - that’’s the horsepower it takes to maintain level flight. Let’s just pick a random number of 80 HP for level flight. That means the excess HP available for climb with the 150 motor is 70, and with the 160 is 80 - that’s a much bigger delta than 150/160...so the climb gain can be significant.

Of course, if you live at sea level in the flat lands, you might very well not care....
 
With my Catto 70x70 2-blade and 160-hp IO-320-D1A I saw 166 KTAS during my Phase 1 testing at 8000' DA. This required spinning the engine to just over 2800 rpm...fine to do once but I don't care to repeat it. Top speed is interesting to document, but I'm no Reno air racer! Prop is rated to 3200 rpm.

Typical LOP performance cruise for me is about 2650 rpm, which works out to 153-155 KTAS.

My top speed is pretty close to 169 KTAS (195 mph), the number Van's lists in the specs for this airframe/engine combo.
 
Last edited:
This may be heresy regarding the "huge" difference but...

...having flown my -9A with 160hp and a constant speed prop for a few years now, I'm reasonably confident I'd be 99.4% as happy with it if it had 150hp and a fixed-pitch. I doubt it would lose very much performance--and it could lose a TON of performance and still be awesome. :)

Perhaps I'd feel differently if I were flying out of Leadville or something.

I haven't actually figured out my top speed at 8,000 feet etc., but it certainly isn't much (if anything) over 160kts. I flight plan for 150kts and generally fly around at close to that speed.

Any significant improvement you will see will be in take-off and climb. You will notice VERY little improvement in cruise speed.
The delta between hp vs. cruise speed is not linear.
 
it takes hp^3 to get speed. ask any crew at reno. its easier to clean up the airframe and get speed than it is to get it with HP.
 
Back
Top