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Engine Decision

N55CU

Member
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Finished with the tail kit. Q-build fuselage & wings are due in next week via Tony Partain (drive carefully) & I want to make my engine & propeller choice soon. Am seeking some performance #'s from those of you with the O-320 with fixed prop versus the IO-360 & constant speed. The latter has been my first choice but if the cruise performance is close I would rather put more money into the avionics.
Thanks,
Randy Utsey RV-7
Charlotte, N.C.
 
I get 205 mph @ 8000 msl (at 1800 lbs gross)in my 7A using an 0-360 A1A (180 hp carbureted) with the new 74" Hartzell Blended Airfoil prop. Throttle is wide open at 2400 rpm. Simple installation and reliable. Flying for over a year and a half squawk free. My completed plane, painted with interior, weight is 1117 lbs with a 79.33" EWCG. Climb rate is over 1800 fpm at gross. I followed Van's recommendations and used their engine, prop, and FWF kit. In retro, I wouldn't do anything different.

Roberta
Flying and Lovin' it!!
 
Chaff and Hay.

Sourcing information on the Net can be very misleading, as you do not know the qualifications of the source. Everybody is an expert. I could tell you that I was a CFI at an Australian Aero Club and recently retired from flying Seattle Heavy Metal out of Hong Kong. But then I might be suffering from delusions of grandeur. You don?t really know.
What is more useful than advice and anecdotal evidence, is being pointed in the right direction to obtain the info you need to make a decisions. Before you can search for the information you need to decide what you want to do with your RV-7. Circuits, Aerobatics or cross-country or all of the above.
One place to start would be to consider an IO360 from Aero Sport Power.
They build IO-360 engines far superior to the production line engines. They are blue printed, hand assembled with the best components and test run and tuned before shipping. Besides that, they are thousands of dollars cheaper the Lycs. Don't take my word for it. Check it out.
http://www.aerosportpower.com/
Fuel injection will give you much more even fuel distribution to each cylinder than any Carby can and consequently when you lean the mixture on the cruise ALL cylinders will be operating near optimum, not just the hottest cylinder. Importantly, Fuel Injection is not subject to Carby Icing.
For more info start with:
http://www.gami.com
A constant speed prop, besides giving better take-off and climb performance, sure! (if you think you need it) But it will also allow you much better control of engine operation.
http://www.avweb.com/news/columns/182146-1.html
Roberta is quite right that you won't be able to better her fixed pitch cruise performance at 8000'DA. However, a fixed pitch prop can only be optimised for one condition. You can't always fly at 8000' and if you are at 1000' you won't have a wide open throttle on the cruise, which is inefficient. Similarly, if you are at 8000' and want to cruise at 55% power for range, again you won't have a wide open throttle.
As for all this drivel about weight. Van's figures for an RV-7 give a ROC solo weight (1400lb) of 2200fpm and at gross weight (1800lb) of 1650fpm. Simple arithmetic shows that for every 10lb increase in weight you will decrease the ROC by 13.75fpm. Even a 20lb increase in weight will not give you sleepless nights, even if you could read the difference on your VSI.
Oh! And you would loose 0.036 mph cruise speed for every 20lb.
The information is all out there. Sorting the chaff from the hay is the problem.
Good luck.
Pete.
 
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