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Thanks, Bill for pointing out the subtle
differences. I generally stay with what my aircraft/engine likes even if I
don't always have an accurate understanding of what is going on. I don't
care if larger TB are "suppose" to be "better" - if my engine doesn't like
it, then I don't like it. {:>).
I think the real message here is that our operating
regime is different from the racer and the better we understand those
differences the more optimum our system will be for operating
regime. As yourself, Tracy, Lynn (and others have put it) bigger is
not always better. Folks like yourself and Lynn who have real world
experience with the racing side (be it rotary engines or others)
understand this. But for many, lacking that experience, we try to "think"
our way through it - which if you don't understand the impact/influence of all
the variables in all the situations (and their very complex interaction) -
just might lead you to a false conclusion.
I know when I started out with an inadequate
understanding of what producing power meant - I looked around for someone to ask
questions of and found no one (no fly rotary type e mail list
then). Well, not quite correct, some of the rotary racing crowd
tried to help, but their focus was completely different from mine. Not
their fault, I tried to follow/copy their approach. But, I soon realized
that what works great for the racer may really "suck" in our
application.
Again, referring to a comment , Lynn, made about
large TB having minimal effect on the tuned length whereas the opposite is true
for a small TB. Since my tuned length is undoubtedly on the long side with
21" between port and TB, this may be another factor why changing the TB in
my case made such a difference.
The nicest thing is you guys with the real
experience convey it to us for no $$ and all we have to do is listen and ask
questions - even "dumb" questions. Its really an asset to have you guys on
the list.
Ed
----- Original Message -----
Sent: Wednesday, May 02, 2007 11:37
AM
Subject: [FlyRotary] Re: Throttle body
size/ other "Paul" issues
Ed,
You are RIGHT. What Lynn is refering to is that with effort, you
can tune for that if your system is sofisticated enough, and your injectors
have enough headroom. (This would require a lot of fuel, RIGHT NOW) MAP
sensor, Throttle angle sensor, and rpm sensor should allow you to tune for
rapid throttle opening, but that doesn't mean that it will be easy. If I have
a choice I err on the side of smaller rather than larger. Lynn in in a racing
application, which is a bit different. My comment is just because you can do a
thing doesn't always make it the correct choice. Your 65mm TB is WORKING stay
with it. FWIW
Bill Jepson
-----Original Message-----
From:
eanderson@carolina.rr.com
To: flyrotary@lancaironline.net
Sent: Wed, 2
May 2007 5:30 AM
Subject: [FlyRotary] Re: Throttle body size/ other "Paul"
issues
Humm, that very interesting, Lynn. The
primary reason I removed the 75 mm TB and reinstalled the 65mm TB was that the
engine would "bog" upon rapid opening of the throttle with the larger dia
TB.
If this was not caused by the large TB then I
guess I'm wondering what was causing it as the rest of the induction system
was the same. My thinking (apparently in error) was that the sudden
change in "effective" area by opening the large TB had a momentary impact
on the air velocity in the runners thereby causing the
hesitation..
Ed
----- Original Message -----
Sent: Wednesday, May 02, 2007 1:58
AM
Subject: [FlyRotary] Re: Throttle body
size/ other "Paul" issues
On further review,
TB size should have no affect on throttle
response at all in an ijected system.
In our carbed engines, rapid
throttle opening drops manifold pressure to ambiant and flow through the
booster venturi is not adequate to match the fuel flow to the throttle
position and the engine falls on its face for lack of fuel. Thus the
accellerator pump and jet system, which pees a long stream of fuel into the
hole while the engine winds up enough revs (and air flow) to engage the
boosters and get a fuel mist pouring into the carb.
No such drama
should be required in the injected engine. Should the TB open in less than X
amount of time could not the injectors closest to the engine stand wide open
for one or two revolutions, or cycles? Or even just some period of time
longer than normal?
So, it should not matter at all how big the TB
is, as it is not even required until you want to slow or shut down the
engine. If there is a butterfly in the inlet tract, the tuned length is
usually figured from that, and not the total length as from the opening into
the air filter or inlet bell. Notice the slide valve throttles on big time
race engines. No affect on the tuned length. That throttle shaft and
butterfly screws up the tune, and shortens the tuned length.
On the
old Formula Continental engines, stock 1600CC VW water cooled engines with
the heads and decks shaved to give huge compression with stock parts, the
injection was free. So what did the smart people use for injection? High
pressure mechanical with high pop pressure injectors, that shot a nasty
looking stream of fuel, not a nice fog of fuel at all. The injectors were
mounted in the center of long bell shapes, and that fast moving stream
of fuel was part of an ejector system that was used to boost airflow to the
tune (pun) of 175 HP from a 54 HP VW Rabbit engine.
So the bigger
the TB the less it should affect the tuned length, and conversly the smaller
the TB the more it should affect the tuned length.
For a reference
the difference between carbed and injected engines with a restrictor
in the injected system the same size as the choke in the carbed engine as 5
to 8 HP. This is mostly the loss of the booster venturi in the center of the
hole.
The improvement in a carbed engine between 36MM and 38MM
chokes is about 5 HP. Per Daryl Drummond. Race engine builder.
Is
this fun to think about or what?
Lynn E.Hanover
----- Original
Message -----
Sent:
Tuesday, May 01, 2007 12:27 PM
Subject:
[FlyRotary] Re: Throttle body size/ other "Paul" issues
Interesting Lynn,
For the comparison that is 2,035 square mm inlet area. Assuming the
bigger 13B could use 1/3 More inlet area the total would be 2,646 square
mm. The inlet area of the 65 mm throttle body is 3,318 square mm.
Seems like a 65 mm TB would be more than up to the task. A 60 mm TB
is 2,827 square mm for reference. Plenty big Buly
Bill Jepson
-----Original Message-----
From:
lehanover@aol.com
To:
flyrotary@lancaironline.net
Sent: Tue, 1 May 2007 9:08
AM
Subject: [FlyRotary] Re: Throttle body size/ other "Paul"
issues
Two 36MM chokes is enough for 244.8 HP at 9,400 RPM, and About 176 HP
at 7,000 RPM. I am in California and the dyno sheet is in Hebron Ohio. But
I can quote it when I get back if it would help anyone.
Lynn E.
Hanover
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