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Jerry,
If you have time sit down and do the calculations
in port areas, it's surprising.
All housings have two ports, usually one
big and one small which add up to approx 2 sq". The a proper street port
area is 3 sq"( 1.5sq" ea). Restrictions cause less HP so a inlet about the same
size would be appropriate.
Although advice on the street ports is that
the smaller port opening of 1.18sq" feeding the 1.5 street port is adequate
with smoothing, quite obviously enlarging the port somewhat while
doing the smoothing etc. Let's say that is goes from 22% to 16 % less
area.
So 3 sq" (3 sq" is 50mm Dia), less
16% ( 3 sq" less 16% = 2.52 sq") = 46mm. Now lest say the PP is 25% better
than the Street port. We take 41% (16%=25%) of 3 sq" = 1.8 Sq" that's
still 38mm dia. I don't think you can go below that without bogging down the
HP
I think 1.5/1.6 will flow 8,000 just fine but not
for the VE for higher HP, I think 1.5 will give about 100hp - nothing startling,
you can get that out of a street port ( with perfect idle) but to get the
extra I need ( 115 to 125), I have to look further. The street port set up
perfectly, may give 116 hp at 7,500; then again it may not, so I am convinced
the PP has the advantage.
I also agree that side ports don't flow as well as
a P- port, one reason may be is that the PP is open a lot longer (
longer duration I call it).
I have confirmed in my own mind that the exhaust
contamination with the early opening P-port is the main contributor to the idle
stumble. For this reason I have selected a reasonably late P-port - strange
thing it equates almost exactly to the factory P-port timing. After measuring
the degree markings, this measures 44mm between IO/ IC.
That will do me, so I have opted for a 44mm
inlet ( we are only arguing a couple of mm here as the 1.6mm = 40.6mm) with a
later opening similar to the stock PP. I will feed that opening with a
44mm ID SS Tube ( 44 = only 1.73" Dia)
The thing to remember is that the calculations for
the carbies are done on piston engines which can create more velocity, where the
rotary only see restrictions - very important point, when looking at
carbies.
The stock PP seems to have a lot bigger D shaped
opening, don't quite understand that, but presume that the flat side of the D
postpones the IO and/or the larger area in the initial IO may override any
residual exhaust pressure, but I'm guessing.
George (down under)
George,
those hp claims seem wildly exaggerated to me. I have never
heard anyone claim 200 hp for a two rotor street port at 7500 rpm.
But I hope they do turn out to be true. I accept the Power Sport numbers
of around 107.5 hp per rotor with a 1.5 i.d. p port. Perhaps if
they had turned 7500 rpm they might have made somewhat more hp.
According to calculations done for my original p port, a 1.5 i.d.port
will flow 8000 rpm just fine. Side ports are relatively terrible
when compared to a p port. I don't think their comparable size has
relevance. Jerry
On Jul 24, 2007, at 6:10 PM, George Lendich wrote:
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
<003501c7ce3f$7b719010$c66b1fd3>
<003601c7ce3f$7b719010$c66b1fd3>
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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