Dave Arbogast wrote:

Can we safely turbocharge / port a Renesis to achieve 310 hp? Or is it safer
to
do so with the 20b?

How much would a new Renesis cost from Mazda? The one on ebay is over 5k and
has
not reached the reserve yet.
--
-dave

http://arb.net

Hello Dave,

How many psi of boost would you have to give to achieve the 310 hp? at sea
level?  Assume you are thinking about the 247 hp. 6 side port RENESIS?

Doug fir

The problem with that Doug is as of right now there are no low compression rotors out
there for the RENESIS RX8 engine. My guess is 10 psi would make 310 HP for
you on the current engine. IMHO if you try 10 psi with the current high compression
RX8 rotors you risk detonation.

Paul Lamar

BTW I think a bit more explanation is needed on the RX8 engine. Yes it is rated
at 8500 RPM. That implies that you find a 3:1 psru and run the prop at 2830 RPM
for takeoff. That is possible for a 65 inch or so prop but that is not
the prop you need for a heavy aircraft let alone an amphibian. This is because the
tips of the prop run into a drag brick wall drastically increasing the
HP consumption without transferring the engine HP to thrust.

The situation is worse with a 2.85:1 gear box. In that case prop RPM would
be 2980. In any event for a heavy airplane you are going to need a large
diameter prop around 72 to 74 inches. Max prop RPM and I am guessing here is down
around 2400 to 2500 hundred so you will not achieve the max HP of the RX8
engine. My guess is 7300 engine RPM or about 220 HP is all you are going to
get with a 72" to 74" PROP and an RX8 high power engine. Not the automatic 
RX8 engine. A turbo charger can make up for this of course.

For good MPG at cruise you will need to slow the airplane and the engine RPM 
for best BSFC. That will require a variable pitch prop. Best BSFC never occurs
at high engine RPM due to engine friction.  Another factor is the tip velocity 
of the prop at a given RPM increases with forward speed. The tip velocity is 
the vector sum of the forward velocity and the circumference velocity of the 
tip. See the chart below.

Right at the moment and well into the future I will not be able to predict 
what that power and engine RPM setting is because Mazda does not release a 
BSFC map for any of the engine they have made. It is going to be best
done by experiment on a specific airplane.

Here is an old summary of the problem from a pre WW II book.

Paul Lamar
 
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