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Jerry,
Sounds good!
The Street port single will give about 116hp at
7,500, but you need 1.18 x2 sq" minimum ( 2.36 sq") = 44 Dia
inlet.
David McCandles has found some old info, which I
will forward under separate cover, which confirms these numbers although I
haven't read it through myself as yet.
The RX8 uses smaller runners but more of them, the
inlet area is massive in total, the smaller runner maintains the velocity.
However because the Rotary doesn't suck like a piston engine ( sucking creates
velocity) the advantages of velocity over area needed, are
limited.
The 12A and 13B are the same size P-port 43mm, the
timing/position are the same.
We have to start to accept that they know the
advantages of sizing and position.
George
George,?
I just got back from Oshkosh which would have been a wasted trip except that I
got to fly a CH 701 amphib off the water.? This was a first for ?yours truly.
? ?What a lot of fun.? The airplane handles perfectly and is the right one for
me. ? ?It is limited by the designer to 100 hp and 200 lbs for the engine
installation. So I am in the in enviable situation of not wanting to get too
much out of my p port. The plane was powered by a 100 hp Rotax.? ?It did very
well.? ?
Re your analysis comparing side ports with p ports, I wonder if such an
analysis is even possible as they are quite different.? Anyway, I doubt that a
standard port can deliver 100 hp or a street port 130 hp. per rotor, certainly
not when limited to 7500 rpm.? Of course I am only guessing.? No real
knowledge or experience.??
The only carb I saw at Oshkosh was the aero carb.? It is sized by HP and
they recommend the 38mm for? 125 to 160 hp.? This is too large for my
purposes.? I am considering going down to 35mm? (90 to 125 hp) ? ?The problem
is that I already have 38mm p ports.? Also, of interest is that they do not
recommend ram air. That simplifies the plumbing and the cowl. ? ?The demo
engine had rather long, small dia runners and an air filter attached to the
carb.? That is the "system." ((on an 80 hp v.w.))? ?If I can get the drive
figured out, ?I will build it with RB's aluminum side plates and Atkins
eccentric. ?BTW the 701 is a high wing. ?The system will be strictly gravity.
? ?? ?Jerry
On Jul 21, 2007, at 10:14 PM, George Lendich wrote:
Jerry,
I'm trying to compare the carb
inlet area to port or P-port areas.
Standard Port area 32 deg ATDC
to 50 degree ABDC = 1.18 sq " each side (x2 = 2.36sq")-
using the front and back housings only.
?
A street port will be 1.5sq" x 2
= 3sq"
.
A 44mm P-port =
2.35sq"
A?42mm p-port =
2.14sq"
A 40mm P-port =
1.94sq"
A 38mm P-port =
1.75sq"
So you see a side port on a
single has more port area than a small P-port.
Perhaps the velocity will make
up for less area.
The street port is bigger again
at 3 sq" - this equates to 50mm port.
?
The standard port gives about
100 hp, the street port about 130hp each rotor.
I wouldn't want to choke down
the port areas with too? restrictive inlet carby?area. I can't see how a 38mm
will cut the mustard when your own calculations suggest 1.6 P-port = 42mm
sq".
?
In reality I'm only looking for
130HPat most, if I can get that.
?
I can run a 41mm ID SS tube
p-port with a 42mm Carby ( and hope velocity makes up the difference) Or I
can run with two 1.5 street ported side ports 3 sq" with two smaller carbs,
perhaps 2x32mm.
?
BTW street ported 13B has been
dynoed to 264hp can't remember the RPM - it might have been higher than what
we run.
More confused than
ever!
?
Does anyone know the IO/IC and
size and HP?of the factory P-port.
?
Lynn, does the timing given,
calculated by the rotor uncovering and covering the port, or the side seal
uncovering/covering the port opening?
I was thinking the RX8 rotor
will be slightly different (bigger) with the harased
edges.
George ( down
under)
?
?
?
?
----- Original Message -----
Sent:
Sunday, July 22, 2007 9:17 AM
Subject:
[FlyRotary] Re: carbs vs efi
George,? maybe I have the wrong idea, but I don't
understand why you need such a large bore carb for the single rotor.? No
way you are going to produce more than 150 hp.? I think 38mm would be
enough.? This is what Aero Carb recommends for the 0-320.? Jerry
On Jul 21, 2007, at 5:56 PM, George Lendich wrote:
Jerry,
Looks like Pat was wrong
about Revmaster having a 44mm, the biggest they go to is 42mm ( at the
present time)?and that costs $380. If I remember the 32mm costs
$320.
Jerry I would be interested
in feed back on what you thought about the Aero Carb, especially how
it's constructed - their all a little
different.
I do like the Ellison but
it's too bloody expensive.
George ( down
under)
George,?
the web site says $326.00.? You might want to compare the aero carb
which is similar.??http://www.aeroconversions.com
I will be looking at both at Oshkosh on Tuesday and Wednesday
next week.? Jerry
On Jul 20, 2007, at 10:06 PM, George Lendich wrote:
?
I have been surprised at the
recent flurry of carb postings.? I assumed that everyone was doing
EFI.? having experienced total electrical failure in march on a
trip to the Bahamas I was thinking a lot about that Neanderthal
carb bolted under my O320 and the magnetos, all unaware of what
was going on in the radio, GPS,?and nav lights departments.??? the
reality is that you don't want a reserve battery to get you to the
ground safely, you want to get to the Bahamas and back and THEN
look into what's wrong.
my questions are "how much
power/performance is lost with a carb, and which carbs can do
manual mixture?".? is it stupid to ask if the Lycoming carb could
run a 13B?? someone mentioned Harley carbs?having a?good history
of rough service.? what about marvel/schebler?? is this question
heresy? :-)? isn't efi a bit of overkill for an engine that
basically runs at 100% power, 75% power and idle?? scanning thru
the archives I see a lot of postings regarding mixture, mapping,
abrupt failures and such.? does this complexity buy us 5%, 20%??
the question of turbo-charging seems to?beg similar line of
questioning.??? kevin
?
Kevin,
It's probably my fault, with a
number of chaps helping me out with
information.
My Buddy Bill Jepson will tell
you nothing beats EFI and when it's running well, he's absolutely
right!
Not only that it is the best
for? fuel efficiency, leaning reading fuel flow etc.
etc.
However I'm developing a single
rotor and looking at all sorts of issues including cost
effectiveness of less elaborate installations. I'm also not keen
on high pressure
fuel under the
cowl.
Most importantly I'm not?an
electronics person and seeing the problems experienced by others
has me more than a little nervous, in regard to
EFI.
Of course I know very little
about carbies, so their helping me with this as
well.
The Revmaster might be the
choice for me, but I'm awaiting the sticker
shock!
George ( down
under)
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