Mailing List flyrotary@lancaironline.net Message #66847
From: Charlie England ceengland7@gmail.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Tuning
Date: Sat, 5 Jun 2021 10:49:35 -0500
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Those that are already flying are much better equipped to answer the tuning question, but IIRC, Tracy has talked about one of the 'problem areas' of tuning that can't be tuned on the ground  is the high rpm/low MAP region as you'd see in a decent. Might be worth a dive into the archives to see what he recommended.

On port diameter: The 'conventional wisdom' is that you need to maintain some (not well defined) level of air velocity in the manifold runners. So it logically follows that the entire length should be the same diameter. Some tuning techniques use a tapered runner that is smallest at the valve (our intake port) so that the air is accelerating as it reaches the combustion chamber, but seems to me that simply necking down the port at the side of the block would just create a really bad flow separation at that point.

On 6/5/2021 9:51 AM, Matt Boiteau mattboiteau@gmail.com wrote:
High power isn't an issue with timing.

I'm trying to understand when you are on base/final and your prop is driving the engine.

Do we treat it like coasting down hill in a car? 

Under 40kpa and 4500rpm, what timing does Tracy computer use?

On Fri., Jun. 4, 2021, 09:47 Matt Boiteau mattboiteau@gmail.com, <flyrotary@lancaironline.net> wrote:
  Sorry I missed all the replies here.

Charlie - I'm measuring both in/out of oil and coolant. Usually when I list the temp numbers, I try to say which one it is. Sorry about that.

The P-Port Renesis engine that I have, got 2" p-ports from Paul. Which sounds like they are too big? I wonder how I can bring them down to 1.75"? Is the inlet to the engine more important, or the whole length of the runners to be 1.75"?

I still don't have a good answer for timing tables for the Rx8. Having a bit trouble tuning for the low RPM's for downwind / final. I know for cars, you can cut the fuel and raise the timing to coast downhill. Not sure for airplanes, since the prop is driving the engine, how we tune for that. Right now I have 38degree timing for descending. I wonder if I should drop that down to the low 30s and not try to lean it out like a car.

- Matt Boiteau
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