Joey said:
Do you any specific performance goals in mind? The factory RV-9a pulls off 180mph at 6gph with a carbed o-320... That's pretty freakin good in my book.
That kind of performance makes you wonder if the extra cash and weight of fuel injection and/or electronic ignition in this case would even be worth it.
Not trying to talk you out of it, of course. Just thinking out loud.
I agree that the RV9A should perform exceptionally no matter what engine is placed in it. However, my desires for what type-size engine to use are based on my ideas concerning utilizing efficient design and economics more than for extracting the most speed out of the airframe. I do not buy into the notion that using carbs and mags is a better fit for an airplane engine. True these are simpler systems. But they are not totally without their problems. If we wanted to always "stay with what works" we wouldn't be flying anyway. We would still be sitting on a horse riding to work and shoveling manure to avoid stepping in it. I fervantly believe in striving to improve things. I absolutely do not believe that carbed, magneto driven Lycosaurs are the best engine alternative to choose from just because that is the way it has always been done.
Ok, my desires for an engine:
1.) I do not want a carburetor on anything newer than a 1965 Ford Mustang because I think that component of engine operation can be more efficiently managed by fuel injection. It has been unrefutably proven over the past 50 or 60 years that fuel injection is a much more efficient means of providing fuel to an engine. I do not want to have to deal with carb icing for one but I also think fuel injection is much more efficient.
2.) Another aspect of the engine setup I desire is electronic ignition. Again, mainly for effieciency and managability of the engine. I believe in new technology, even if it takes the aviation industry 50 years to accept it.
3.) Of course weight is a primary concern. I have been going back and forth on whether it is worth putting a CS prop on the airframe or going with a FP cruise prop. I don't think this airplane "needs" a CS prop to perform and since the CS does weigh more I am leaning toward the FP. Just haven't made up my mind yet.
The weight issue has me looking at the differences between the IO-320 and the IO-360 (and now the IO-340). I have been informed there is a 12-15 lb. difference between the IO-320 and the IO-360. I am concerned about an aft CG if I go through with my plans to modify the baggage compartment as Norman Hunger has done to carry two sets of golf clubs (click
here to see his mods). If I make the modification, the weight difference of the IO-360 would help with CG when the baggage area is loaded down.
4.) Fuel used is also important to me. Not only is 100LL getting more and more expensive to the point that I wonder how I will afford to put fuel in my airplane but it will also be going away in the near future. I do not want to have to concern myself with figuring out what to do as a replacement. I like auto fuel. I think it is a perfectly good fuel. I think Ethanol is a perfectly good fuel source also. In fact with its high octane level (120-130) I think it could be a good replacement for 100LL even. It does take more of it than gasoline to get the same mileage but it does burn cleaner. I think it can work well in our engines when they are designed for it. Because of these things I do not want an engine that is "forbidden" from using anything except 100LL.
5.) Another issue is price. Although I don't like the price of any engine package if I buy new, the difference between the IO-320 and IO-360 in price is negligable. The difference between the O v IO versions of these engines is not enough to keep me away either when I consider the conveniences I can gain by using FI.
6.) My plans for flying this airplane include flying into the Rocky Mountains of Colorado, New Mexico, Wyoming, Montana, Utah, etc. Given the additional 20 HP the IO-360 will provide if I go with the 180 hp version over the 160 hp IO-320, I lean toward the IO-360 for having the extra hp for getting out of high density altitude mountain airports.
So those are the major determiners for what engine I desire. The IO-340 sounds very interesting because it is lighter than an IO-360 while providing equal to or perhaps more hp. However, the requirement for using 100LL only has me concerned. I still don't know yet what I will end up doing. One of these days I will have to make a choice and commit to something. For now I will continue to evaluate all the options including auto conversions.
RVBYSDI
Steve