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Craig,
Some questions about the power
required to run a supercharger to normalize or, say, up to 40% boost
--
my old B&M Supercharger book says that using a
clutch to disconnect the supercharger only saves 3% in fuel ... referring to a
less efficient roots-type blower. That makes me wonder if someone's
earlier note that a blower required -- was it 70 hp? -- was maybe off by a
digit? Sounds like 7 to 15 hp would be closer... for about 40%
boost. It would help to quantify.
Evidence that this smaller
blower power requirement might be in the ballpark, is from Power Transmission
Design Handbook, for computing HP ratings for belts... mine was a 'C'
crossection belt, or close to it, i think, driving a McCulloch (Paxton) centrifugal blower on the 351 ci Windsor in my
Magnum bushplane, and it was driven nicely by its 3/4" standard automotive
V-belt, no problem pumping 42" MP at 4500 rpm. No waste gate used. I
was probably running the blower too fast, as the intake temp was
about 180F... (didn't have to worry about carb ice). ; ) (See
CONTACT! Magazine issue 16)
Another indication that not much
power is needed to drive the supercharger was a study Vortech did for my
installation, which showed that for 40% boost, only 14.9 HP input to their
supercharger would be needed.
So my thinking is that although a 300-400 hp engine
with a turbo wouldn't use any crank HP, my belt-driven blower
used only about 4 to 5% to blow a 45% boost, and the manifolding was
much simpler and much cooler inside the cowling. Does this sound
reasonable?
Wish I'd had a dyno for some better data. The
B&M book charts for this engine with my mods showed (estimated) about 380
HP, up from unblown about 270. Any other comments on engine HP needed to
drive a centrifugal supercharger?
T.
----- Original Message -----
Sent: Wednesday, March 16, 2005 06:39
PM
Subject: [LML] Re: supershargers
Has
anyone tried mechanically linking the throttle to a variable
wastegate on
the manifold between supercharger and carburetor?
I was thinking that this
way possibly the more-opened-up wastegate could
let the pressure blow off
when the throttle was pulled back, and increase
the blow-off level as the
throttle was opened. Terrence
What has been
done, is use an electric clutch similar to the A/C
compressor
clutch to
disengage the supercharger at low RPM or where boost is not
required.
In my opinion, the only real advantage of a mechanically driven
supercharger is
low RPM response. I can't see the need in an aircraft. Maybe
aerobatics??
Craig
Berland
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