Right prop for RV-9 IO-320?

I am well into my flight testing but I don't think the prop I have (Sensenich 79" that Van's recommends and as supplied as part of my engine/prop package) is correct. At WOT (though at full rich), I get maybe 2,420 PRM in level flight. During takeoff, I get no more than 2,200 RPM, and this is with a fairly shallow departure (in order to keep CHT's down). This RPM makes me nervous, as Sensenich says to avoid operation between 2,150 to 2,300 RPM due to engine/prop resonances.

At a 2,300 RPM cruise with a Density Altitude of around 4,500 feet, I am indicating 120 kts with a TAS of 128 kts (148 mph). I don't have fairings, so this speed is somewhat reasonable. But, with the top RPM not very much higher than the restricted range, and with takeoff occurring in the restricted range, it would appear I have a mismatched propeller.

Any thoughts?

Dump the Sensenich and call Craig Catto.

Don't make any rash decisions until you have all the fairings on.
An increase in airspeed will allow the rpms to come up.

On the other hand, I can't discount Bill's suggestion either. I'm a STRONG believer in Catto Props!

Mel said:

Don't make any rash decisions until you have all the fairings on.
An increase in airspeed will allow the rpms to come up.
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Sorry, I missed that you didn't have your fairings on yet. As Mel said, wait until you have them all on before making any changes.

Remember, you will gain close to 10 MPH/Knots for the gear leg fairings and 5 MPH/Knots for the wheel pants. That will let the RPM come up. It will also help your cooling as you will be pushing more air through the cowling.

Sounds like good advice, but are there any comments on operating in the restricted range? I guess this applies for long term operation, but a lot of takeoffs and full power climbs eventually adds up to a lot of time.

I have a 160hp XP-IO-320 with an 81" Sensenich and it runs about 2220 rpm static and 2340 at 110 knots indicated while climbing at WOT. It will just exceed 2600 rpm in speed runs at 1000 ft and 7500 ft but I have all the fairings on. It may be worth checking your MP reading at WOT. Mine is 29.6" at 50 ft above sea level during the takeoff run. Maybe your throttle is not quite wide open.

I may have the opposite problem with my Catto. With no fairings or wheel pants on and at about 75% power (about 2500 rpm), I'm showing around 135 knots TAS at about 5-6K density. At WOT, full rich, I can easily get it to go above the engine red line of 2700. I'm guessing I'll have more problems once I get the fairings on and once I start using the mixture knob. ???

For a prop pitched primarily for cruise, at what density altitude should full throttle in straight and level flight normally result in near-red line engine rpms? Stated differently, is there such a set of numbers one looks for to determine proper pitch on a prop?

Steve, it depends on your priorities. At about 8000' density altitude I can run WOT and LOP at just under 2400 rpm which is a good economical full throttle cruise. If I wanted better takeoff performance or to cruise LOP at 2500 rpm I would have a 79" pitch. But judging by the numbers you are getting with no fairings your prop needs to be re-pitched higher even to be a normal "climb" prop.

My Whirlwind GA200 has been great

I swapped out my Sensenich last year for a WW Ground adjustable prop. Took a few attempts to pitch it correctly, but now I have it dialled in nicely. As with any fixed pitch prop there are compromises, however I pitched mine for max RPM at cruise (in order not to redline). I get 2150 static. Solo I get 2200+ fpm climb - dual I get 1700++ fpm. It is always hard to give a top speed number due to test conditions . . . Im happy though getting 7.5-8.0 gph at 75% with cruise speeds (ranging from 145-160kts) Great all around performer.

Do NOTHING with the prop ...

Until you are sure that the plane is all cleaned up with fairings AND that you are getting good reading from ALL instruments.

I have run that combo (as well as the Catto). There are 10;s of knots still to be had.

James