| Matt: Yes i agree the 2 inch p- ports is a way “overkill“ for aviation and more for racing where you can go up to 12 000 rpm. For aircraft use you run out of prop rpm before the 2 inch intake runners reach optimum VE - Volumetric Efficiency. This was my main reason why i decided to p-port a 13B turbo engine motor and the availability in South - Africa. I build my engine on the basic principles that the late Steve Beckham did it.
Was difficult for me to get info on the Beckham build and design, as that was also “intellectual capital” at that time. I got hold of a unused lycoming engine exhaust system. It is build out of a specific type stainless steel, not sure what type stainless ,but the inside diameter is 44 mm ( 1.73 inch) and it seems that this was the “sweet diameter” for the intake runners. The intakes runner must be between 21 to 28 inch and the specific length must be adjust afterwards for optimum VE , say on 7500 engine rpm.
At least i would not be kicked off the group 😅😂🤣 for my opinion, but helped by guys with more experience than me. As Lynn H always say “ I could be wrong”
Le Roux
Sent from my iPhone Le Roux Breytenbach On 05 Jun 2021, at 21:12, Matt Boiteau mattboiteau@gmail.com <flyrotary@lancaironline.net> wrote:
Yeah I went up to 8000' feet the other day and did some simulated circuits. Was hoping someone would give me a good starting point to see if I'm on the right track. Yeah I don't know why Paul L got the machine shop to drill 2" p-ports. Seems quite large.
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?
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.
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