|
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
|