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Nevertheless, Lynn,s comments safed my day.
I was trying to tune the single rotor over the past few weeks. Using a 38mm
Mikuni round slide, I got it to idle clean up from 1600rpm. Transition into
midrange and up to WOT is no problem. Trying to get the mixture
richer at WOT, I did not get the responce to enlarging the main jet I
expected. The mixture stayed lean, indicated by high EGT and white plug
insulators, to some extend suported by the O2 reading. The air flow rate at 6000
rpm is almost double of what Mikuni says is max. I started wondering.
Now Lynn said " carbs get leaner to the top of their RPM ranges" . There
may be the answer to my problem: bigger carb!
Richard Sohn
N2071U
----- Original Message -----
Sent: Saturday, August 18, 2007 8:22
AM
Subject: [FlyRotary] Power! More Power,
Scotty! was [FlyRotary] Re: Air/fuel flow
Lynn's summation says it all (if it ever is all said
{:>)).
The bottom line is that atmospheric oxygen to support
combustion is the limitation in making power. You can always add more
fuel if you could just get more air/oxygen into the combustion
chamber.
Using atmospheric pressure alone there is only so much
pressure to force air (approx 20% oxygen) into the combustion chamber.
Some combination of tuning can improve on chamber stuffing over atmospheric
pressure alone, but I think even here you are only talking about 105-110%
VE. To really increase power beyond this point you either need to go to
some sort of forced induction or to an oxidizer like nitrous oxide to provide
more oxygen to burn more fuel to made more power.
But, other than that - volumetric flow (CFM) says it
all. Anything done to improve it aids power, but unfortunately, the
things done to improve it at one rpm may well hurt VE at another rpm. So
pick your power band and tune your induction system accordingly.
Ed
----- Original Message -----
Sent: Saturday, August 18, 2007 8:37
AM
Subject: [FlyRotary] Re: Air/fuel
flow
Lynn,
The question was on inlet velocity for a Mazda rotary at 7,500 rpm -
if you happened to have some info on that.
Everyday cars have 450' per sec and race cars 125' per second,(
suggested on a carb site) Ed's calculations used 176' per second
which indicated a bigger inlet diameter. I was thinking about 300 to 350'
per second would more like it, but I have no real hard
data!
Well then let me speculate.
The engines have two RPM where they wander above 100% VE. These are too
low to help us much but the car designers use this and stretch it out a
bit looking at the pipe organ intakes.
Just off idle and about 2,000 RPM. This confuses the idle and
transition circuits in the Weber and you get a
nice Rumppp...Rumppp...Rumppp. Breathing is very good compared to a
piston engine, and runner diameter is small for any HP output. The stock
intake manifold gasket in my engines (Daryl Drummond) is barely enlarged at
all. The new engine may have more than two such RPM.
Porting extends the intake open time and makes for a more turbine like
flow. Even a street port can nearly double the stock HP, and that would
require nearly double the stock airflow. Down low the race or even street
ported engine has little advantage over the stock engine. For any RPM the
air flow determines the HP output, so where (RPM) you are interested in
output there will need to be dramatically improved airflow.
So generally, the displacement times the RPM minus some percentage for
inlet restriction based on TP size or carb choke size and or runner length
and diameter will be the stock situation and one CFM value.
And in a modified intake system with longer runners of slightly more
diameter which will favor the same RPM as the stock example engine will
have very much more power than a stock engine at the same RPM, indicating a
much higher than stock (CFM) air flow. Maybe not over 100% VE but much
closer to that number than the stock engine.
There is no cheating possible here. So if your example engine is
compared to any other engine with more power at the same RPM. The higher
power output requires very much more airflow, not less.
Something is amiss Watson.........I can feel it!
Lynn E. Hanover
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