tubo vs super -- Re: [s-cars] was, 0-60 , 1/4mile, now:Re: superchargers are bad, mmkay?

[Mark Strangways]

Which leads one to wonder why they offer the turbo, and / or twin turbo to
this day.
Obviously a positive displacement pump powered off a connection to the
crankshaft will do better.
Where it will not do better is mid RPM high load. If a blower is meant to be
run at 6000 rpm, it will only deliver half of it's available flow at 3000
RPM.
A turbo will deliver more flow at this lower RPM simply because it is NOT
coupled to the crank.
While it may not flow 100 % of it capacity at 6000 RPM, it will deliver more
than 50 % capacity at 3000 RPM.
Unless I have fallen off my bar stool here...

Mark S
----- Original Message ----- 
From: "mlp5" <mlped at qwest.net>
To: "'Richard Harris'" <rnharris at bellsouth.net>; "'Calvin & Diana Craig'"
<calvinlc at earthlink.net>; "'Gabriel Caldwell'" <gabriel at ts.bc.ca>; "'Bill
Clancy'" <clancybill at yahoo.com>; <s-car-list at audifans.com>
Sent: Sunday, June 06, 2004 10:58 PM
Subject: RE: tubo vs super -- Re: [s-cars] was, 0-60 , 1/4mile,now:Re:
superchargers are bad, mmkay?


FWIW, in his book, Forced Induction Performance Tuning, A. Graham Bell, a
Kiwi or Aussie, offers the following tidbits under the rubric "What Porsche
Discovered - .... Porsche did some comparison testing on a 16-valve 2.5
liter 944 some time back with both a Roots blower and a turbocharger.
Figures 9.4 & 9.5 (available to those who may care on request) show two sets
if the results. .... The Roots blower made close to maximum boost within
about 2.5 seconds of the throttle being floored.  By comparison the turbo
car has virtually no boost at this stage (the 2.5 second mark)  In fact it
take over 10 seconds for the turbo to make the same boost as the blower.

"Things were just as dismal for the turbo in terms of actual acceleration.
After 5 seconds, the blown car has accelerated from 1150 rpm to 2050, while
the turbo car has barely increased engine speed.  After 10 seconds, the
blower car has reached over 2,800 rpm with the turbo languishing at just
2,000 rpm."

"Porsche reported that at 6,000rpm, the blower consumed 50hp.  However in
the low and middle range, it had a torque advantage of 50% - 70% over the
turbo car.  Only in out right power and fuel economy was the turbo car
superior.  Maximum power was up 19% and fuel consumption was down 9%.

"For those who believe flooring the accelerator at 1150 rpm in 4th gear is
not a valid test, as it favors the blower over a turbo Porsche report that
they tested every possible combination of initial speed and gear.  But in
every test the blower car out performed the turbo car by 10% - 40%."  pgs
137-138

Bell doesn't state WHEN these tests were run, or under what engine
management conditions &/or systems were available at the time.  My
assumption is this was done as a part of the testing and development for the
944 (type 951) cars, so say @ the mid 1980's.

mike

>-----Original Message-----
>From: s-car-

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