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Proper RPM range on new engine

PeteP

Well Known Member
I have an stock O320E3D in my 9A with 2.6 hrs SMOH and no test stand run in. It is swinging the Vans recommended Sensenich 70CM prop pitched at 77 inches. The engine is complete stock in terms of pistons, mags, carb and etc. Also the prop has a max RPM limit or 2600.

At this time, according to the Skyview with a Vans tach generator, it will only turn up 2450 RPM WOT in cruise at 5 or 6K altitude with good CHTs and EGTs and truing out at about 125 knots. I have not yet installed the wheel pants or gear leg fairings.

I am going to try to check the tach with an external tach to verify the Skyview accuracy this weekend. I found the Sensenich specs on the prop and they call for a minimum static RPM of 2100 - 2250 RPMs which I am pretty sure I am making but will check again.

Could this be an engine break-in issue or an over pitched prop issue? .
 
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Sounds like over pitched prop. Is your E3D 150 or 160 hp? Either way it could be over pitched. I sold a Catto two blade to a fellow with a similar issue on a 9A and that solved his issue. It was a 70"x70" of Cattos previous design (2013, with nickel leading edge"). It was slightly under pitched for my 160hp D1A from Aerosport.
 
True air speed or indicated? You will gain a lot by the drag reduction of wheel and gear leg fairings, 12 knots or better.
 
A stock O320E3D should generate 150Hp @2700 RPM. The 77" pitched prop is the correct prop for this engine and should not be over pitched.

Won't hurt to verify the Skyview RPM, if not accurate you can use the P signals from the mags as input to the Skyview rather than a tach generator.

BUT... I suspect the low RPM reading is due to the fact you don't have the pants and fairings installed. These significantly affect top speed which also affects the top RPM of your engine. I wouldn't worry too much about your low RPM readings until you get the pants and fairings installed.
 
Unlikely you have a tach error, all it has to do is count pulses. :)

Sounds like you have a good engine, get all the fairings and pants installed and you should be happy with the performance. The Sensenich is a very nice prop with excellent field history. I've been flying one for 16 years.
 
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Run it as hard as you can for the first 15-20 hours and after you put on the gear leg fairings and wheel pants you will see an immediate increase in speed due to the reduced drag. That should help get the RPM's on the prop up. Cruising around LOP in my -9A I see 2500-2550 RPM and get 148-152Kts TAS. Turning up the mixture I can get 162Kts TAS @ 2700 RPM, but burn about 3 gallons an hour more. The -9A likes to fly high, so don't be afraid to get up above 8000'.
 
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