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Permalink Reply by Bob Pustell on September 18, 2018 at 11:05am

It would all depend on the O-320 you installed. Since you are not worried about certified requirements you could use any number of "hot-rodding" options available for the O-320. Even a certified O-320 can have an STC'd high compression kit installed that makes it a 160HP engine. A PowerFlow exhaust supposedly adds ten horsepower. There is a certified and legal 170HP right there, in an engine that weighs a bit less than a stock O-360. Now, if you start adding various uncertified things like electronic ignition, cylinder head porting and polishing, etc you could get even more power. Basically the O-320 would have a slight weight advantage over the O-360 which would partially offset the lower power output. Then you could add power to the engine and actually increase performance. It all depends on how creative you want to be and how much money you want to spend.

A final consideration - O-360 cores are expensive because so many RV series planes use them and demand is high. O-320 cores will cost you a lot less as a beginning to build on.

Have fun!

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Permalink Reply by Jeffrey Goodrich on September 18, 2018 at 2:17pm

Thank you Bob! I appreciate the info. I did not know about increasing an 0320. I find it a little hard to find out info on the CH 801 and that really helps

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Permalink Reply by Bob Pustell on September 21, 2018 at 7:37pm

Glad to help, even if in general terms only. Another point to consider is -- those hot rodding options are available for the O-360 also. So, if you started with an O-360 and boosted the performance of that engine you would have a real rocket ship. A stock O-360 gives pretty good performance already. A hot rodded O-320 would most likely match the stock O-360.

Final thought - a constant speed prop adds weight and complication but greatly improves performance since the full rated power of the engine is available for take off and climbout and for cruise. An O-320 with a constant speed prop would most likely outperform an O-360 with a fixed pitch prop. Again, life is full of trade-offs. There are some interesting electronically controlled uncertified constant speed props available now that would go nicely on either an O-320 or an O-360. They weigh less than the certified ones and don't have the weight and complication of a mechanical prop governor, as well. Also, you can fit one of the electronically controlled ones onto an engine that is not equipped to mount a conventional constant speed prop and governor combination.

A fixed pitch prop is kind of like a one speed transmission in a car - you can have good low end performance (lock the transmission in first or second gear, a climb prop) or you can lug like heck at take off and climbout and then go faster once you get to altitude and start cruising (lock the transmission in third or fourth gear, a cruise prop). A constant speed prop lets you take off in first gear (fine pitch blade angle), climb out in second and third gear and then shift into high gear for cruise (a coarse blade pitch to bite the air effectively at high speed). That lets you have better performance on less power because you can use all the horsepower in all flight situations. A fixed pitch prop can only let the engine develop full power in one part of the flight, the rest of the time it is not being efficient.

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Permalink Reply by Jeffrey Goodrich on September 21, 2018 at 10:44pm

Great information Bob! I would have never thought of a CS prop on this build , but  it makes sense. Best of both worlds. I think the 0 360 is probably the right choice. I was thinking cost when I really should be thinking performance. Thanks again for sharing your knowledge.

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