http://parrisracingconcepts.com/Home_Page.php
This
is the latest “turbo crank” deal, being aggressively marketed to
snowmobile people now. Turbo crank mods are cicada-like, coming around,
being promoted and talked about every few years, then going away.
Is this like
the deal that [then TX highschool roadracer Colin Edwards’ race team manager] David Herold tested here at DynoTech with you [as team performance consultant] 20 years ago on the [90 HP Yamaha roadrace bike] TZ250? I
recall you saying at some point [prior to the dyno test] it couldn’t possibly provide meaningful power or airflow boost
because the crank wheels were traveling well below the speed of sound [even at 12,000 RPM]. [The stock crank and “turbo” crank as you predicted delivered identical airflow CFM and HP].
Jim C
KC’s response:
The important variable in the design of a centrifugal compressor is its tip
speed – the velocity of the impeller tips. The impeller accelerates the air
molecules to tip speed, and compression takes place as this energy of motion is
converted in the diffuser into the energy of pressure. There is a strict
elationship between the two.
circumference in feet times revolutions per second. If the flywheels are 5″
diameter the circumference is about 16 inches, or 1 1/3 feet. If crank rpm is
8500 then revolutions per second are 142. Multiplying the two together gives us
a “tip speed” of under 190 feet per second.
Various Speeds” I find that an adiabatic pressure rise (adiabatic means with no
exchange of heat) of 2% results from 100% efficient operation. Since the crank
flywheels are not equipped with a diffuser as centrifugal compressors are, it is
unlikely that much of this 2% would appear at the bottoms of the transfer
ducts.
a wheel with a tip speed of 1200 fps.
vaporization.